praseodymium and iron incorporated alpo-5...

PRASEODYMIUM AND IRON INCORPORATED

AlPO-5 MOLECULAR SIEVES FOR ORGANIC

TRANSFORMATIONS

A THESIS

Submitted by

SUNDARAVEL B

in partial fulfillment of the requirements for the degree of

DOCTOR OF PHILOSOPHY

FACULTY OF SCIENCE AND HUMANITIES

ANNA UNIVERSITY

CHENNAI 600 025

MAY 2014

ii

ANNA UNIVERSITY

CHENNAI 600 025

BONA FIDE CERTIFICATE

Certified that this Thesis titled “PRASEODYMIUM AND IRON

INCORPORATED AlPO-5 MOLECULAR SIEVES FOR ORGANIC

TRANSFORMATIONS” is the bona fide work of Mr. SUNDARAVEL, B.

who carried out the research work under my supervision. Certified further that

to the best of my knowledge the work reported herein does not form part of

any other thesis or dissertation on the basis of which a degree or award was

conferred on an earlier occasion on this or any other scholar.

Place : Chennai Dr. V. MURUGESAN

Date : SUPERVISOR

Professor of Chemistry (Retd.)

Anna University

Chennai 600 025

iii

ABSTRACT

Homogeneous catalysts such as sulfuric acid, hydrochloric acid,

hydrofluoric acid, phosphoric acid, etc., are frequently used in the chemical

industry. However, these catalysts are environmentally hazardous, toxic,

corrosive and non-recyclable. Porous materials such as zeoloites, zeotypes

and mesoporous solids have emerged as an alternative option for the chemical

industry due to their non toxicity, non corrosive nature, possibility of reusing

and more importantly their ecofriendly nature. The use of heterogeneous

catalysts is highly desirable for compliance with the principles of green

chemistry, offering low energy routes to products, eliminating the

requirement of auxiliary species and facilitating catalyst recovery to minimise

waste generation. The use of porous solid acids as heterogeneous catalyst is

gained significant importance in organic synthesis due to their environmental

compatibility combined with good yield and selectivity.

The isomorphously substituted AlPOs found applications in aerial

oxidation of linear and cyclic hydrocarbons using molecular oxygen.

Compared to zeolites, MeAlPO molecular sieves possess large variety of acid

sites and broader acid sites distribution. Because of these valuable properties,

metaloaluminophosphates (MeAPOs) become one of the important materials

as heterogeneous catalyst for important organic transformations. The present

work focused on the synthesis, characterization and catalytic evaluation of

PrAlPO-5 and FeAlPO-5.

PrAlPO-5 with different (Al+P)/Pr ratios (25, 50, 75, 100, 150 and

200) were successfully synthesized by hydrothermal method in fluoride

iv

medium. These molecular sieves were characterized using XRD, DRS UV-

vis, BET, SEM, TEM, 27Al and 31P MAS-NMR ESR, XPS, TPD-NH3, ex-situ

pyridine adsorbed IR, TPR, TGA and FTIR studies. The incorporation of

praseodymium in the framework of AlPO-5 was confirmed by XRD, DRS

UV-vis and 27Al and 31P MAS-NMR spectra. The increase of lattice

parameters also supported the incorporation of Pr in AlPO-5 framework. ESR

spectrum revealed the presence of adsorbed oxygen. The ammonia-TPD study

confirmed the presence of weak and moderately strong acid sites whereas

ex-situ pyridine adsorbed IR spectrum confirmed the presence of Lewis acid

sites. The BET surface area of PrAlPO-5 was found to be in the range of

239 – 272 m2g-1. The textural parameters varied linearly with increase in

praseodymium content. The hysteresis loop observed just below the relative

pressure (p/p0) of one is due to inter-particle voids. The SEM and HRTEM

images also revealed such large number of voids due to aggregation of

particles.

Iron containing AlPO-5 with AFI topology was synthesized

hydrothermally in fluoride medium. The framework incorporation of Fe3+,

and the absence of separate iron(III) oxide phase in AlPO-5 were confirmed

by XRD and DRS UV-vis studies. The tetrahedral geometry of iron in [FeO4]-

was identified by ESR and DRS UV-vis studies. The ammonia-TPD study

revealed the presence of weak acid sites in FeAlPO-5. The ex-situ pyridine

adsorbed IR spectrum confirmed the presence of Lewis acid sites. The

textural parameters especially average pore size of fresh and used FeAlPO-5

catalysts remained almost the same and in good agreement with the parent

AlPO-5, suggesting that the zeotype kept its original structure.

v

The catalytic activity of PrAlPO-5 (25, 50, 75 and 100) was tested

in the liquid phase aerobic oxidation of ethylbenzene. Acetophenone was

found to be the major product with more than 90% ethylbenzene conversion.

PrAlPO-5 (25) showed better selectivity than other catalysts at 120 °C in 6 h

reaction time. The decrease of (Al+P)/Pr ratio increased the conversion and

selectivity. This correlated the dependence of Pr content in AlPO-5 and

reactivity. It was also observed that weak and moderately strong acid sites

created by the framework incorporation of praseodymium in AlPO-5 favored

side chain oxidation rather than ring hydroxylation. Further, the change in

electron density around the benzylic hydrogen did not influence the selectivity

to acetophenone. This study concluded that ethylbenzene and different

substituted ethylbenzenes could be effectively oxidized using molecular

oxygen as oxidant over PrAlPO-5 at 120 oC. The ICP-OES analysis

confirmed the presence of praseodymium intact in the framework of AlPO-5

up to five cycles.

The catalytic activity of PrAlPO-5 (75, 100, 150 and 200) was

evaluated in the synthesis of campholenic aldehyde from -pinene.

Campholenic aldehyde was found to be the major product whereas -pinene

oxide, verbenol and verbenone were identified as minor products in the liquid

phase oxidation. The influence of reaction parameters such as temperature,

reaction time, solvent and Pr content in AlPO-5 was optimized with a view to

obtain campholenic aldehyde selectively. The epoxidation of -pinene by

chemisorbed oxygen followed by isomerisation of -pinene oxide over Lewis

acid sites on PrAlPO-5 yielded campholenic aldehyde selectively. Thus

PrAlPO-5 was proved to be active, selective and reusable catalyst.

vi

Synthesis of 5-arylidene-2,4-thiazolidinediones was carried out in

water-ethanol (4:1) solvent system at 100 °C over FeAlPO-5 (75, 100 and

150). Though the reaction proceeded faster in polar solvents like dimethyl

sulphoxide, acetonitrile and ethanol, the reaction parameters such as

temperature, iron content and reaction time were optimized in water-ethanol

solvent system with a view to design a greener route for the synthesis of 2,4-

thiazolidinedione (TZD) derivatives. The Knoevenagel condensation of

substituted benzaldehydes with TZD also showed 90% product selectivity

with high aldehyde conversion. Further, the structure of isolated products was

confirmed by 1H-NMR spectra.

The bi-functional nature of PrAlPO-5 catalyst will open new

prospect for potential application in the synthesis of fine chemicals. Further, it

is also concluded that FeAlPO-5 is an efficient catalyst for Knoevenagel

condensation.

vii

ACKNOWLEDGEMENT

I take this opportunity to express my profound thanks and

wholehearted gratitude to my supervisor Dr. V. Murugesan, Professor of

Chemistry (Retd.), Anna University, for his valuable guidance, stimulating

discussions, constant encouragement and moral support during the entire

course of my research work.

I am grateful to Dr. M. Palanichamy, Professor of Chemistry

(Retd.), Anna University, Chennai, for his unstinted support and valuable

suggestions. I thank Dr. P. Kannan, Professor and Head, Department of

Chemistry, Anna University, Chennai, for providing facilities to carry out my

research work. I record my sincere thanks to Doctoral Committee member,

Dr. M. Kandasamy for his valuable inputs.

I am thankful to the Department of Science and Technology, New

Delhi, for the award of Junior Research Fellow and financial support to carry

out this research. I wish to express my sincere thanks to Dr. S. Devika,

Dr. B. Palanisamy and Mr. C. M. Babu for their support for successful

completion of my work. I also like to thank my seniors and friends for their

support.

Finally, I extend my sincere gratitude to my beloved parents, brother

and sisters for their constant encouragement, forbearance and patience during

the entire course of my research work.

(SUNDARAVEL B)

viii

TABLE OF CONTENTS

CHAPTER NO. TITLE PAGE NO.

ABSTRACT iii

LIST OF TABLES xv

LIST OF FIGURES xvii

LIST OF SCHEMES xxi

LIST OF SYMBOLS AND ABBREVIATIONS xxii

1 INTRODUCTION 1

1.1 CATALYSIS 1

1.2 CATALYSIS AND GREEN CHEMISTRY 2

1.2.1 E-Factor 3

1.2.2 Atom Efficiency or Atom Economy 4

1.3 HETEROGENEOUS CATALYSIS 5

1.4 POROUS MATERIALS 6

1.5 ZEOLITES 6

1.5.1 Structure of Zeolites 7

1.5.2 Nomenclature of Zeolites 9

1.5.3 Classification of Zeolites Based on

Pore Size 10

1.5.4 Unique Properties of Zeolites 10

1.5.5 Applications of Zeolites 11

1.5.6 Molecular Sieves Versus Zeolites 11

1.5.7 Non-aluminosilicate Molecular Sieves 12

1.6 GENERAL ASPECTS OF

ALUMINOPHOSPHATES 13

1.6.1 Natural Aluminophosphates 15

ix


1.6.2 Synthetic Aluminophosphate Molecular

Sieves 16

1.6.3 Nomenclature 17

1.7 STRUCTURAL ASPECTS OF


1.7.1 Classification 20

1.7.2 Neutral Framework 20

1.7.3 Anionic Framework AlPOs 23

1.7.4 Bonding Patterns 23

1.8 TOPOLOGICAL CHEMISTRY OF


1.8.1 Building Units 24

1.8.2 Al and P Coordinations and

Stoichiometries 27

1.9 TEMPLATING IN THE CONSTRUCTION OF


1.9.1 Types of Templates 28

1.9.2 Role of Templating 31

1.10 ISOMORPHIC SUBSTITUTION 33

1.10.1 Metal Aluminophosphates 35

1.11 AlPO-5 MOLECULAR SIEVE 36

1.12 CATALYTIC APPLICATIONS OF MeAPO-5

MOLECULAR SIEVES 37

1.13 SCOPE AND OBJECTIVES OF THE PRESENT

INVESTIGATION 44

x


2 EXPERIMENTAL METHODS 47

2.1 MATERIALS 47

2.1.1 Chemicals 47

2.2 PREPARATION OF CATALYSTS 48

2.2.1 Synthesis of PrAlPO-5 48

2.2.2 Synthesis of Praseodymium Oxide 49

2.2.3 Synthesis of AlPO-5 Supported Pr6O11 49

2.2.4 Synthesis of FeAlPO-5 49

2.2.5 Synthesis of Fe2O3 50

2.3 CHARACTERIZATION OF

SYNTHESIZED MATERIALS 50

2.3.1 X-ray Diffraction (XRD) 51

2.3.2 Diffuse Reflectance Ultraviolet -

Visible Spectroscopy 53

2.3.3 Nitrogen Sorption Studies 53

2.3.4 Fourier Transform - Infrared

(FT-IR) Spectroscopy 56

2.3.5 Thermogravimetric Analysis

(TGA) 57

2.3.6 Temperature Programmed

Desorption (TPD) 58


Reduction (TPR) 59

2.3.8 Scanning Electron Microscopy

(SEM) 60

2.3.9 Transmission Electron

Microscopy (TEM) 61

xi


2.3.10 X-ray Photoelectron Spectroscopy

(XPS) 62

2.3.11 Electron Spin Resonance (ESR)

Spectroscopy 63

2.3.12 Magic Angle Spinning - Nuclear

Magnetic Resonance (MAS-NMR)

Spectroscopy 64

2.3.13 Inductively Coupled Plasma–

Optical Emission Spectroscopy

(ICP-OES) 65

2.4 CATALYTIC STUDIES 66

2.4.1 Liquid Phase Reactions 66

2.4.1.1 Oxidation of ethylbenzene 68

2.4.1.2 Synthesis of campholenic

aldehyde from -pinene 68

2.4.1.3 Synthesis of 5-arylidene-

2,4-thiazolidenedione 68

2.5 PRODUCT ANALYSIS 69

2.5.1 Gas Chromatograph 69

2.5.2 Gas Chromatograph Coupled with Mass

Spectrometer 69

2.5.3 NMR Spectroscopic Analysis 70

3. PHYSICO-CHEMICAL CHARACTERIZATION

OF PrAlPO-5 AND FeAlPO-5 MOLECULAR

SIEVES 71

3.1 INTRODUCTION 71

xii


3.2 PHYSICOCHEMICAL CHARACTERIZATION

OF PrAlPO-5 72


3.2.2 Diffuse Reflectance Ultraviolet Visible

(DRS-UV-Vis) Spectroscopy 74

3.2.3 Surface Microstructure

(SEM and HR TEM) 76


3.2.5 Electron Spin Resonance

Spectroscopy (ESR) 80

3.2.6 X-ray Photoelectron

Spectroscopy (XPS) 83

3.2.7 27Al and 31P Magic Angle

Spinning – NMR 84


Reduction (TPR) 88

3.2.9 Characterization of Acid Sites

(TPD-NH3 and ex-situ pyridine

adsorbed IR) 89

3.2.10 FT-IR Spectroscopy 92

3.2.11 Thermogravimetric Analysis (TGA) 93

3.3 PHYSICOCHEMICAL CHARACTERIZATION

OF FeAlPO-5 95


3.3.2 Diffuse Reflectance Ultraviolet –

Visible Spectroscopy 97

3.3.3 Scanning Electron Microscopic

(SEM) Analysis 99

xiii



3.3.5 Electron Spin Resonance

Spectroscopy (ESR) 101

3.3.6 X-ray Photoelectron

Spectroscopy (XPS) 102

3.3.7 Characterization of Acid Sites

(TPD-NH3 and ex-situ pyridine

adsorbed IR) 103

4 LIQUID PHASE AEROBIC OXIDATION OF

ETHYLBENZENE OVER PrAlPO-5

4.1 INTRODUCTION 106


4.2.1 Effect of Temperature 110

4.2.2 Effect of (Al+P)/Pr Ratios 112

4.2.3 Effect of Reaction Time 112

4.2.4 Effect of Substituents 113

4.2.5 Catalyst Recycling 115

4.2.6 Conclusion 115

5 SYNTHESIS OF CAMPHOLENIC ALDEHYDE

FROM -PINENE OVER PrAlPO-5 116



5.2.1 Effect of Temperature 121

5.2.2 Effect of (Al+P)/Pr Ratios 121


5.2.4 Effect of Solvents 124

xiv


5.2.5 Structure Identification of Products 125

5.2.6 Catalyst Recycling 130

5.3 CONCLUSION 130

6 SYNTHESIS OF 5-ARYLIDENE-2,4-

THIAZOLIDINEDIONES OVER FeAlPO-5 131



6.2.1 Effect of Temperature and Al/Fe Ratios 136


6.2.3 Effect of Solvents 138

6.2.4 Effect of Substituents 139

6.2.5 Structure Identification of Products 142

6.3 CONCLUSION 153

7 SUMMARY AND CONCLUSION 154

7.1 SUMMARY AND CONCLUSION OF

THE PRESENT WORK 154

7.2 SCOPE FOR FUTURE WORK 158

REFERENCES 159

LIST OF PUBLICATIONS 178

xv

LIST OF TABLES

TABLE NO. TITLE PAGE NO.

1.1 E factors in various segment of chemical industry 4

1.2 Structure type index as per IUPAC nomenclature 9

1.3 Classification of zeolites based on pore openings 101.4 Structure of aluminophosphate based molecular sieves 18

1.5 Acronyms for framework composition 19

1.6 Structures of AlPO4-n molecular sieves 221.7 Templates used for the preparation of specific

structure type 29

3.1 Lattice parameter values for AlPO-5 and PrAlPO-5 743.2 Nitrogen sorption results of calcined AlPO-5 and

PrAlPO-5 (25, 50, 75, 100, 150 and 200) 80

3.3 TPD-NH3 sorption results of calcined samples 91

3.4 Lattice parameters for calcined AlPO-5 and FeAlPO-5 97

3.5 Nitrogen sorption results for fresh and used

FeAlPO-5 catalyst 101

3.6 TPD-NH3 sorption results of calcined FeAlPO-5 catalysts 105

4.1 Effect of reaction temperature and (Al+P)/Pr ratios on the

oxidation of ethylbenzene 111

4.2 Effect of substituents on benzylic oxidation 114

5.1 Effect of reaction temperature and (Al+P)/Pr ratios on the oxidation of -pinene 122

5.2 Effect of solvents on the oxidation of -pinene 124

6.1 Effect of reaction temperature and (Al+P)/Pr ratios in the synthesis of 5-benzylidene - 2, 4 – thiazolidinedione 137

xvi

TABLE NO. TITLE PAGE NO.

6.2 Effect of solvents in the synthesis of

5-benzylidene - 2, 4 – thiazolidinedione 139

6.3 Effect of substituents in the synthesis of

5-benzylidene - 2, 4 – thiazolidinedione 141

xvii

LIST OF FIGURES

FIGURE NO. TITLE PAGE NO.

1.1 Secondary building units identified in zeolite frameworks 8

1.2 Representative AlPO4-n molecular sieves with different

pore openings 21

1.3 Secondary building units (SBUs) found in AlPO4-n based

framework 25

1.4 Eight distinct 2D sheet structures

(The SBUs constructing these sheets are also shown) 26

1.5 Cylindrical channel in AlPO-5 and the stacking of

encapsulated tetrapropylammonium hydroxide species 30

1.6 Partial periodic table with transition elements introduced

into aluminophosphates and silicoaluminophosphates 36

1.7 Framework topology of AlPO-5 (a) framework structure

of AlPO-5, (b) 12-ring channel view along (001) plane

and (c) 12-membered ring of AlPO-5 37

2.1 Schematic diagram of multiple reflection ATR system 56

2.2 The interaction between primary electron beam and

the sample in an electron microscope 60

2.3 Catalytic reaction set up for liquid phase reactions 67

3.1 XRD patterns of calcined (a) AlPO-5, (b) PrAlPO-5 (25),

(c) PrAlPO-5 (50), (d) PrAlPO-5 (75), (e) PrAlPO-5 (100),

(f) PrAlPO-5 (150), (g) PrAlPO-5 (200) and (h) Pr6O11 73

3.2 DRS UV-Vis spectra of (a) AlPO-5 and (b) AlPO-5

supported with 3 wt%Pr6O11 75

xviii


3.3 DRS UV-Vis spectra of (a) PrAlPO-5 (200), (b) PrAlPO-5 (150), (c) PrAlPO-5 (100), (d) PrAlPO-5 (75), (e) PrAlPO-5 (50) and (f) PrAlPO-5 (25) 75

3.4 SEM images of (a) AlPO-5, (b) PrAlPO-5 (200), (c) PrAlPO-5 (150), (d) PrAlPO-5 (100), (e & h) PrAlPO-5 (75), (f) PrAlPO-5 (50) and

(g) PrAlPO-5 (25) 773.5 TEM images of (a) AlPO-5, (b) PrAlPO-5 (200),

(c) PrAlPO-5 (150), (d) PrAlPO-5 (100), (e) PrAlPO-5 (75), (f) PrAlPO-5 (50) and (g) PrAlPO-5 (25) 78

3.6 N2 sorption isotherms of (a) AlPO-5, (b) PrAlPO-5 (200), (c) PrAlPO-5 (150),

(d) PrAlPO-5 (100), (e) PrAlPO-5 (75),

(f) PaAlPO-5 (50) and (g) PrAlPO-5 (25) 79

3.7 Small angle XRD pattern of PrAlPO-5 (75) 79

3.8 Room temperature ESR spectra of PrAlPO-5

samples 81

3.9 Low temperature ESR spectra of (a) PrAlPO-5 (25)

and (b & c) PrAlPO-5 (75) 83

3.10 XPS spectrum of calcined PrAlPO-5 (75) 84

3.11 27Al MAS-NMR spectra of AlPO-5 and PrAlPO-5

(25 and 75) 85

3.12 31P MAS-NMR spectra of AlPO-5 and PrAlPO-5

(25 and 75) 87

3.13 TPR profile of (a) AlPO-5 supported 3 wt% Pr6O11,

(b) PrAlPO-5 (100), (c) PrAlPO-5 (75),

(d) PrAlPO-5 (50) and (e) PrAlPO-5 (25) 88

xix


3.14 TPD-NH3 profile of (a) AlPO-5 and (b) AlPO-5

supported 3 wt% Pr6O11 89

3.15 TPD-NH3 profile of (a) PrAlPO-5 (200), (b) PrAlPO-5

(150), (c) PrAlPO-5 (100), (d) PrAlPO-5 (75),

(e) PrAlPO-5 (50) and (f) PrAlPO-5 (25) 90

3.16 Ex-situ pyridine adsorbed IR spectra of (a) PrAlPO-5

(150), (b) PrAlPO-5 (100), (c) PrAlPO-5 (75) and

(d) PrAlPO-5 (25) 91

3.17 FT-IR spectra of (a) AlPO-5, (b) PrAlPO-5 (200),

(c) PrAlPO-5 (150), (d) PrAlPO-5 (100),

(e) PrAlPO-5 (75), (f) PrAlPO-5 (50) and

(g) PrAlPO-5 (25) 93

3.18 TGA of as-synthesized (a) AlPO-5,

(b) PrAlPO-5 (100), (c) PrAlPO-5 (75),

(d) PrAlPO-5 (50) and (e) PrAlPO-5 (25) 94

3.19 TGA of calcined (a) AlPO-5, (b) PrAlPO-5 (100),

(c) PrAlPO-5 (75), (d) PrAlPO-5 (50) and

(e) PrAlPO-5 (25) 95

3.20 XRD patterns of (a) FeAlPO-5 (150),

(b) FeAlPO-5 (100), (c) FeAlPO-5 (75)

and (d) Fe2O3 96

3.21 DRS UV-Vis spectra of (a) FeAlPO-5 (150),

(b) FeAlPO-5 (100) and (c) FeAlPO-5 (75) 98

3.22 SEM images of (a) AlPO-5, (b) FeAlPO-5 (75),

(c) FeAlPO-5 (100) and (d) FeAlPO-5 (150) 99

3.23 Nitrogen sorption isotherms of (a) AlPO-5,

(b) fresh FeAlPO-5 (75) and (c) used FeAlPO-5 (75) 100

xx


3.24 ESR spectra of (a) FeAlPO-5 (75), (b) FeAlPO-5

(100) and (c) FeAlPO-5 (150) 102

3.25 XPS spectrum of calcined FeAlPO-5 (75) 103

3.26 TPD-NH3 profile of (a) FeAlPO-5 (150),(b) FeAlPO-5 (100) and (c) FeAlPO-5 (75) 104

3.27 Ex-situ pyridine adsorbed IR spectra of calcined

FeAlPO-5 (75) 1054.1 Effect of reaction time on ethyl benzene oxidation 113

5.1 Effect of reaction time 123

5.2 1H NMR spectrum of campholenic aldehyde 127

5.3 1H NMR spectrum of -pinene oxide 128

5.4 1H NMR spectrum of verbenone 129

6.1 Effect of reaction time 138

6.2 1H NMR spectrum of 5-(4-nitrobenzylidene)-1-

3-thiazolidine-2,4-dione 145

6.3 1H NMR spectrum of 5-(3-nitrobenzylidene)-1-3-

thiazolidine-2,4-dione 1466.4 1H NMR spectrum of 5-(3-methoxybenzylidene)-1-

3-thiazolidine-2,4-dione 147

6.5 1H NMR spectrum of 5-(2-hydroxy-3-methoxy benzylidene)-1-3-thiazolidine-2,4-dione 148

6.6 1H NMR spectrum of 5-(4-methoxybenzylidene)-1-

3-thiazolidine-2,4-dione 1496.7 1H NMR spectrum of 5-((benzo[d][1,3]dioxol-6-yl)

methylene)1,3-thiazolidine-2,4-dione 150

6.8 1H NMR spectrum of 5-((thiophen-2-yl)methylene)

thiazolidine-2,4-dione 151

6.9 1H NMR spectrum of 5-((pyridin-3-yl)methylene)

thiazolidine-2,4-dione 152

xxi

LIST OF SCHEMES

SCHEME NO. TITLE PAGE NO.

1.1 Generation of Brönsted acid sites in

aluminophosphate molecular sieves 34

4.1 Aerobic oxidation of ethylbenzene 109

4.2 Possible pathway for the oxidation of

ethylbenzene to acetophenone 110

5.1 Synthesis of campholenic aldehyde from -

pinene 119

5.2 Plausible pathway for the oxidation of -

pinene and isomerisation of -pinene oxide 120

6.1 Synthesis of 5-arylidene-2,4-

thiazolidinedione 133

6.2 Plausible mechanism for the synthesis of

water mediated TZD derivative 134

6.3 Plausible mechanism – The role of Lewis

acid sites in the synthesis of TZD derivative 135

xxii

LIST OF SYMBOLS AND ABBREVIATIONS

Å

N

°C

m

%

-

-

-

-

-

-

-

-

-

-

Alpha

Angstrom unit

Avagadro number

Beta

Degree Celcius

Gamma

Magic angle

Percentage

Theta

Wavelength

AlPO - Aluminophosphate

AFI - Aluminophosphate-five

a.u. - Arbitrary unit

BJH - Barrett - Joyner - Halenda

BE - Binding energy

BET - Brauner - Emmet - Teller

CRT - Cathode ray tube

cm - Centimeter

CCD - Charge coupled device

cm3/g - Cubic centimeter per gram

DTG - Derivative thermogram

W/ T - Difference in weight/difference in temperature

DTA - Differential thermal analysis

DRS-UV-vis

D

-

-

Diffuse reflectance ultraviolet visible spectroscopy

Dimensional

xxiii

ESR - Electron spin resonance

eV - Electron volt

EDAX - Energy dispersive x-ray analysis

FID - Flame ionisation detector

FT-IR - Fourier transform infrared spectroscopy

FWHM - Full width at half maximum

GC - Gas chromatograph

GC-MS - Gas chromatograph coupled with mass spectrometer

Hz - Hertz

HMS - Hexagonal mesoporous silica

h - Hour

H2O2 - Hydrogen peroxide

IUPAC - International union of pure and applied chemistry

keV - Kiloelectron volt

kHz - Kilohertz

kJ - Kilojoules

KIT - Korean advanced institute of science and technology

MAS - Magic angle spinning

MRP - Membered ring pore

m - Meta

MeAPO - Metal aluminophosphate

MeAPSO - Metal silicoaluminophosphate

m2g–1 - Metre square per gram

m - Micrometer

s - Microsecond

mg - Milligram

ml - Millilitre

min - Minute

MCM - Mobil composition matter

xxiv

M - Molar

mol - Mole

MOR - Mordenite

nm - Nanometer

NMR - Nuclear magnetic resonance

o - Ortho

p - Para

ppm - Parts per million

PILCS - Pillared interlayered clays

PBU - Primary building unit

RSF - Relative sensitivity factor

rpm - Rotation per minute

SBA - Santa Barbara

SEM - Scanning electron microscopy

SKM - Schuster - Kubelka - Munk

SBU - Secondary building unit

s - Second

SAPO - Silicoaluminophosphate

SSHC - Single-site heterogeneous catalyst

STP - Standard temperature and pressure

SDA - Structure directing agent

TPD

TPR

-

-

Temperature programmed desorption

Temperature programmed reduction

TBHP - tert-Butylhydroperoxide

tert - Tertiary

TCD - Thermal conductivity detector

TGA - Thermogravimetric analysis

TZD - 2,4-Thiazolidinedione

UHV - Ultra high vacuum

xxv

Wt % - Weight percentage

XRD - X-ray diffraction

XPS - X-ray photoelectron spectroscopy

ZSM - Zeolite sacony mobil

1

CHAPTER 1

INTRODUCTION

1.1 CATALYSIS

Catalysis is a process in which acceleration of chemical reaction is

induced in the presence of a material (catalyst) that is chemically unchanged

at the end of the reactionThe phenomenon of reducing the energy requirement

of a chemical process by changing the rate of attainment of equilibrium

through lowering of activation energy is termed as catalysis and the material

as catalyst. However, catalysts do not alter the equilibrium position of a

reaction which is controlled thermodynamically and require high pressures.

Recent estimations revealed that approximately 90% of chemicals ranging

from bulk chemicals to consumer products come into contact with a catalyst

at one stage or another of their manufacturing process. Depending upon their

relative reaction medium catalysts are classified into two basic types,

heterogeneous and homogeneous.

The world wide effort to replace homogeneous acid catalysts by

heterogeneous catalysts in all industries is to control pollution and waste. In

homogeneous type, the catalysts are in the same phase as the substrate and are

uniformly distributed. As the catalyst gets dissolved in the reaction medium

almost all the reactions under homogenous type takes place within the liquid

phase whereas in most cases of heterogeneous system the catalyst used is a

porous solid and the reaction takes place either on its external surface or

surface within the pores of the solid. Heterogeneous catalytic systems, in

2

which fluid reactants are reacted over solid acid catalysts, are the most widely

used catalytic processes in the manufacturing industries at present. The

following are the advantages of heterogeneous systemswhen compared to

their homogeneous counterparts:

Minimal pollution, less corrosion and wastes.

High activity, selectivity and suppression of side products.

Shapeselectivity.

Easy removal of product from the reaction mixture and

efficient recycling of the catalyst.

Use of renewable starting materials.

Easy separation of end products.

1.2 CATALYSIS AND GREEN CHEMISTRY

The concept of green chemistry has gained momentum among

researchers both in academic and industries as a tool for achieving

sustainability by promoting innovative chemical technologies that reduce or

eliminate the use or generation of hazardous substances in the design,

manufacture and application of chemical products. Strong legislative

enactments towards controlling discharge of waste products from industries

into the environment and their restrictions in the manufacture, transport,

storage and use of certain hazardous chemicals has sparked the introduction

of cleaner technologies. Realizing the unsustainable consequences of

exceeding the earth’s natural capacity in dealing with the waste and pollution

which society generates, Anastas&Warner (1998) coined a set of twelve

principles as green chemistry. Heterogeneous catalysis is an omnipotent tool

to realize all the twelve principles of green chemistry.

3

i) Waste prevention instead of remediation

ii) Atom efficiency

iii) Less hazardous/toxic chemicals

iv) Safer products by design

v) Innocuous solvents and auxiliaries

vi) Energy efficient by design

vii) Preferably renewable raw materials

viii) Shorter synthesis (avoid derivatization)

ix) Catalytic rather than stoichiometric reagents

x) Design products for degradation

xi) Analytical methodologies for pollution prevention

xii) Inherently safer processes

Heterogeneous system is more convincing in controlling

environmental pollution. The two significant factors of heterogeneous

catalysts that influence the environmental impact of cleaner chemical

processes are (1) E-factor, and (2) atom efficiency.

1.2.1 E factor

E factor is an important metric to understand the potential

environmental acceptability of chemical processes. It is defined as the mass

ratio of waste to desired product. The magnitude of the waste problems in

chemical manufacture is readily apparent from the consideration of typical E

factor in various segments of chemical industry (Table 1.1). A high E factor

means more waste and consequently more negative environmental impact.

The ideal E factor is zero. E factor can be calculated using the following

Equation (1.1)

4

Kgof secondary productsEfactorKgof desired product

(1.1)

Table 1.1 E factors in various segment of chemical industry

Industry segment Product tonnagea E(kg wasteb/kg product)

Oil refining 106 - 108 < 0.1

Bulk chemicals 104 - 106 < 1to 5

Fine chemicals 102 - 103 5to50Pharmaceuticals 10 - 103 25 to100a Represents annual production volume of a product at one site (lower end

of range) or world-wide (upper end of range) b Defines as everything produced except the desired product (including all

inorganic salts, solvent loss, etc)

For example, the original process of Friedel-Crafts acylation using

AlCl3 had an E factor of about 5 and required a chlorinated hydrocarbon or

nitroaromatic solvent. The new process with zeolite (H-beta)

catalysedFriedel-Crafts acylation, in contrast, has an E factor of < 0.01 and no

solvent is required. The substantially higher E factors in fine chemicals and

pharmaceuticals compared with bulk chemicals is a reflection of more

widespread use of stoichiometric reagent and multi-step synthesis in the

former steps. Thus, replacement of stoichiometric protocols in the fine and

pharmaceutical industries by catalytic methods will help to reduce E factors in

these sectors and thus will help to achieve the goals of green chemistry.

1.2.2 Atom Efficiency or Atom Economy

The concept of atom economy was developed by Trost (1991 and

1995). This is a method of expressing how efficiently a particular reaction

5

makes use of the reactant atoms. Thus if all the reactants are completely

incorporated in to the product, the synthetic pathway is said to 100% atom

efficiency because it will not generate any waste. Atom economy of a

particular reaction can be calculated by the following Equation (1.2).

Atom ef iciency =Molecular weight of the product

Sum of the molecular weight of the reactants(1.2)

1.3. HETEROGENEOUS CATALYSIS

Unlike a homogeneous catalytic system, both the catalyst and the

reactants of a heterogeneous system are in different phases such as solid,

liquid or vapour. Solid acids and their salts find important application as

heterogeneous catalysts. The most common are silica, alumina,

aluminosilicates and aluminophosphates. Industrial processes involving

dehydrogenation, oxidation, ammoxidation and polymerization are catalyzed

using metals, metal oxides, clays and zeolites. A landmark in the history of

heterogeneous catalysis was achieved by Fritz Haber in 1970 (Smil

1999)when he prepared large quantities of ammonia from nitrogen and

hydrogen in the presence of Fe2O3 catalyst using a high pressure reactor.

Similarly oxidation with metallic platinum, dehydrogenation with metallic

nickel and Fischer-Tropsch process over cobalt and iron catalysts are other

examples. Lewis and Brönsted acidities in the catalysts are two fundamental

active centres in most of the solid acid catalysts. Chromia is a well known

example of a Lewis solid acid catalyst (Auroux&Gervasini 1990). On the

other hand bulk oxides with loosely bound protons associated with oxide ions

are examples of Brönsted acid catalyst. V2O5 and ZrO2 contain both Lewis

and Brönsted acid sites (Auroux&Gervasini 1990 and Kawai et al 1981).

Yadav et al(1993) and Yadav&Thorat (1996) have reported alkylation of

6

toluene with benzyl chloride, benzyl alcohol and benzyl ether over sulfated

zirconia.

1.4 POROUS MATERIALS

Porous materials have widespread applications such as catalysts,

catalyst supports, adsorbents and sensors due to their high thermal,

hydrothermal, mechanical and chemical stabilities as well as high specific

surface area, large specific pore volume and pore diameter. The IUPAC has

recommended specific nomenclature for classification of porous materials

into three groups based on their predominant pore size: microporous (pore

diameter < 2nm), mesoporous (2nm < pore diameter <50 nm) and

macroporous (50 nm < pore diameter). Zeolites, zeotype materials and

activated carbons are examples of microporous materials. M41S family,

mesoporousAlPOs, aero-gels and most recent SBA-1, SBA-15 and KIT-5 are

few examples of mesoporous materials. Examples of macroporous materials

include silica-gel, activated charcoal and CPG (controlled porous glass).

1.5 ZEOLITES

Zeolite is a unique class of oxides, consisting of microporous, crystalline aluminosilicates found in nature or synthesized artificially

(Thomas et al 1999). These materials were discovered in 1756 by the Swedish

mineralogist Axel Frederick Cronstedt, who found that the mineral stilbite

lost significant amount of water when heated. The word zeolite stems from

Greek and means boiling stone. It took almost two centuries before zeolite

received the attention of chemists. Nowadays, new zeolites and associated

materials are still being discovered in laboratories worldwide. Zeolites are

used in various potential applications such as household detergents, desiccants

and toothpaste, whereas their acidity makes them attractive catalysts. In the

middle of 1960s, Raboet al(1966) at Union Carbide demonstrated that

7

faujasitic zeolites are very interesting solid acid catalysts. Since then, a wealth

of zeolite-catalyzed reactions of hydrocarbons has been discovered. For

fundamental catalysis they offer the advantage that the crystal structure is

known and that the catalytically active sites are thus well defined. The fact that zeolite possess well-defined pore systems in which the catalytically active

sites are embedded in a defined way gives them some similarity to enzymes.

1.5.1 Structure of Zeolites

Zeolites are crystalline aluminosilicates having three dimensional

framework made up of primary buildings units (PBU) of SiO4 and

AlO4tetrahedra (known as TO4) by sharing a common oxygen atom in their

corners. The PBUs are joined together to form a secondary building unit

(SBU) and twelve such SBUs were identified by Meier & Olson (1987) as

shown in Figure 1.1.These SBUs are arranged in a specific geometrical

pattern to form a definite crystal structure and uniform pore size.

Theoretically thousands of structures can be arrived but only around 160

have been synthesized till today. Out of these, only 40 of them are naturally

occurring zeolites. Zeolites are represented by the following empirical

formula (Breck 1964).

Mx/n [(AlO2)x (SiO2)1-x] . zH2O (1.1)

where M is a cation with valency n, x represents the number of

AlO2tetrahedra and z represents the number of water molecules.

8

Figure 1.1 Secondary building units identified in zeolite frameworks

9

The presence of extra negative charge in the framework,

compensated by cations especially protons, is the main cause for Brönsted

acidity. Lewis acidity is generated by the formation of trigonally co-ordinated

Al and Si sites by the removal of two hydroxyl groups from the framework

(Uytterhoeven et al 1965). While zeolites are synthesized commercially for

specific uses, many natural zeolites are readily available as minerals from the

earth crust. Their unique properties made tremendous applications in

petrochemical cracking, ion-exchange and in separation and removal of gases

and solvents (Piera et al 1998 and Tomita et al 2004). The other applications

are in agriculture, animal husbandry, construction, etc.

1.5.2 Nomenclature of Zeolites

International Zeolite Association Structure Commission and

IUPAC have assigned structural codes to known natural and synthetic zeolites

(Barrer 1983). Designations consist of three letter abbreviation derived from

the names of species which do not include numbers and characters other than

Roman letters. Some examples are shown in Table 1.2.

Table 1.2 Structure type index as per IUPAC nomenclature

Structure type code

Species Structure type code Species

MFI ZSM-5 LAU Laumonite MOR Mordenite LTA Linde Type A MTN ZSM-39 LTL Linde Type L MTT ZSM-23 MEL ZSM-11 BEA Beta AST ALPO-16 MTW ZSM-22 ATS ALPO-36 AEL ALPO-11 ATT ALPO-33 AFI ALPO-5 CHA Chabazite

10

1.5.3 Classification of Zeolites Based on Pore Size

Zeolites exhibit ion-exchange property, extreme thermal stability

and possess channels like pore systems approaching molecular size which

made them attractive for a variety of industrial applications. Barrer (1983)

classified zeolites based on the pore openings(Table 1.3).

Table 1.3 Classification of zeolites based on pore openings

S. No. ClassPore

opening

Pore

diameter (Å) Example

1. Small pore 8 3-4 A, ZK-5

2. Medium pore 10 5-6 ZSM-5, ZSM-11

3. Large pore 12 6-8 X, Y, BEA

4. Ultra large pore 18*, 20# 8-12 VPI-5*, Cloverite#

1.5.4 Unique Properties of Zeolites

The following are the unique and salient properties of zeolites

which made them useful in many areas.

Crystallinity Uniform pore systems

High internal surface area Ion-exchange capabilities

Non-toxic Microporosity

Pore channels or cages High thermal stability

Acidity Environmentally safe

11

1.5.5 Applications of Zeolites

Adsorption:In drying, purification and separation,zeolites can absorb up to 25% of their weight in water.

Ion-exchange: Zeolites are builders in washing powder, where

they gradually replaced phosphates to bind calcium. Calcium

and to a lesser extent magnesium in water are exchanged for

sodium in zeolite A. This is the largest application of zeolites

today as they are essentially non-toxic and pose no

environmental risk. Zeolites are also applied in toothpaste, again

to bind calcium and prevent plaque.

Catalysis: Zeolites possess acid sites that are catalytically

active in many hydrocarbon reactions. The pore system allows

molecules that are small enough to enter and hence it affects the

selectivity of reactions by excluding both the participation and

formation of molecules that are too large for the pores.

1.5.6 Molecular Sieves VersusZeolites

McBain (1932) proposed the term molecular sieve. According to

him molecular sieves are materials with the capability of separating

components in a mixture on the basis of molecular size and shape differences.

The two classes of molecular sieves, namely, zeolites and microporous

charcoals were known when McBain formulated his definition. The list now

includes silicates, metalloaluminates, aluminophosphates, silico and

metalloaluminophosphates, mesoporous and macroporous materials in

addition to zeolites. These materials are structurally analogous but differ only

in their elemental composition. Although all the materials stated above are

molecular sieves, only aluminosilicates carry the classical name of zeolites.

12

1.5.7 Non-aluminosilicate Molecular Sieves

The preparation of zeolites and zeo-type structures containing

framework components other than aluminium and silicon has become need of

the hour to press forward in the area of new molecular sieves. Zeolites offer

ion-exchange property, high thermal stability, high acidity and shape selective

structural features. However, modification and subsequent improvement of

these properties have served as a driving force for changing the composition

of these microporous materials. Structures with pores larger than the known

12 ring type of zeolite Y (ultra large pore molecular sieves) have not yet been

produced in zeolite types. However, structures containing other composition

offer the possibility that such ultra pores may be realized. Aluminophosphate

(VPI-5) containing 18-membered ring (Davis et al 1988) and Cloverite

containing 22-membered ring pore systems (Merrouche et al 1992) have been

synthesized in non-aluminosilicate system. The change of elemental

composition not only produced ultra large pore materials but also added a new

dimension to find tailor-made molecular sieves. Gallium can easily substitute

aluminium, and germanium for silicon in aluminosilicate system. In addition

to these materials, zeo-type structures crystallized in the presence of organic

cations have been claimed to contain boron, iron, chromium, cobalt, titanium,

zirconium, zinc, beryllium, hafnium, manganese, magnesium, vanadium

and tin.

Since tetravalent germanium crystallizes to form molecular sieve

structures, it is also possible for other tetravalent ions that can occupy

tetrahedral oxide sites to crystallize to form such structures. Based on the

theory formulated by Barrer (1984), titanium could substitute into molecular

sieve structures. Perego et al (1986) synthesized titanium contining ZSM-5

structures. CeAlPO-11 was synthesized by Araujo et al (1997) without

13

affecting the structure of AlPO-11. Zahedi-Niaki et al (2000) reported a

comparative study of VAPO-5, -11, -17 and -31 aluminophosphate molecular

sieves.

1.6 GENERAL ASPECTS OF ALUMINOPHOSPHATES

At the onset of 1980s, a novel class of crystalline,

microporousaluminophosphates (AlPOs) was reported by Wilson et al (1982

and 1982a) at the Union Carbide, representing the first family of framework

oxide molecular sieves synthesized without silica. This discovery opened the

door to a new era in open-framework inorganic materials (Cheetham et al

1999). The aluminophosphate molecular sieves known as AlPO4-n(nrefers to

a distinct structure type) were prepared with a wide range of pore sizes by

hydrothermal synthetic technique in the presence of organic amines or

quaternary ammonium cations as templates or structure directing agents

(SDA) (Pastore et al 2005 and Wilson 1991 and 2001). These molecular

sieves are built from strict alternation of AlO4 and PO4tetrahedra. The primary

building units are formed by Al-O-P linkages instead of Si-O-Al or Si-O-Si

bridges of zeolite (Chen et al 1994). The lack of P-O-P and Al-O-Al in these

materials, constraining the structure to be alternate Al and P tetrahedra, limit

the structural building units to only even-numbered rings (Szostak 1989).The

AlPO contains Al3+ and P5+ in tetrahedral position and the resultant

framework is neutral and therefore there are no charge compensating ions as

in zeolites. Thus Brönsted acidity is intrinsic to AlPOs and they are not

suitable for acid catalysis (Pujado et al 1992).

The exciting property of AlPOmaterials is that Al or P can be

replaced by silicon to form SAPO (silicoaluminophosphate) materials resulted

in Brönsted acidity and they can be used as acid catalyst (Gielgens et al

1995). The isomorphous substitution of divalent or trivalent metal ions in

AlPO and SAPO forms MeAPO and MeSAPO respectively (Levi et al 1991

14

andMontes et al 1990). Such substitution introduced charge imbalance in the

framework which was balanced by protons, thus generating Brönsted acidity

and offering catalytic activity and ion-exchange capability in these molecular

sieves (Flanigen et al 1988). The overall composition of aluminophosphate

molecular sieves is represented as xR: Al2O3: 1.0 ± 0.2P2O5: yH2Owhere R is

an organic amine or quaternary ammonium ion. The quantities x and y

represent the amount of organics and water respectively that fills the pores of

the crystal as AlPO requires no counter ions (Flanigen et al 1986). The

aluminium to phosphorous ratio of these molecular sieves is always unity.

Aluminophosphate molecular sieves include more than 40

structures. Among these 25 are three dimensional framework structures, of which at least six are two dimensional layered materials and the others are

microporous. Most of the three dimensional structures are novel. AlPO and

SAPO molecular sieves cover a wide range of structure types, some are analogous to certain zeolites such as SAPO-42 (zeolite A structure), SAPO-34

(chabazite structure) and SAPO-37 (faujasite structure). But there is also a

large number of aluminophosphates such as AlPO-5, AlPO-11 or VPI-5, which possess unique structures with no zeolitic analogue (Davis et al 1988).

Aluminophosphate based molecular sieves exhibit excellent thermal and

hydrothermal stability compared to those observed in stable zeolites. Many are thermally stable and resist loss of structure even at 1000 ºC (Wilson et al

1982). Their surface selectivity is mildly hydrophobic. Their general formula

can be expressed as [(AlO2)x(PO2)x]·yH2O indicating that, unlike most

zeolites, aluminophosphate molecular sieves are ordered with Al/P ratio is

always unity. However, in spite of this, aluminophosphate molecular sieves exhibit enhanced structural diversity.

The discovery of open-framework AlPOs has brought some

conceptual breakthrough for traditional microporous compounds, e.g. the

framework elements are not only limited to Al and Si atoms; the upper limit

15

of pore size is not only delimited to 12-ring; the primary building units are not

only defined to tetrahedral. The on-going search for new structures

particularly provides some mechanistic clues on the formation of open-

framework materials. Ultimately, the crystallisation mechanism of

microporous materials must be understood in order to rationalise the

synthesized materials with desired structures, compositions and properties.

The discovery of AlPOs also improved the current application areas of

microporous materials(Thomas et al 1999 and Thomas 1999). One of the

important and promising areas of application of AlPOs is in catalysis where

aerial oxidations are possible using linear and cyclic hydrocarbons (Thomas

et al 2001). Selective oxidation reactions are also carried out using AlPOs

(Li et al 2010).The nanosized channels of AlPO-n also present suitable host

systems for the fabrication of advanced functional materials such as nanosized

single walled carbon nanotubes (Wang et al 2000).

1.6.1 NaturalAluminophosphates

The interactions between aluminium and phosphorus oxides to form

stable structures occur to a considerable extent in nature. The nine naturally

occurring neutral aluminophosphate minerals are berlinite (AlPO4), variscite

and metavariscite (AlPO4.2H2O), augelite (Al2PO(OH)3), senegalite

(Al2(OH)3(H2O)(PO4)), wavellite (Al3(OH)3(PO4)2H2O), trolleite

(Al4(PO4)3(OH)3), bolivarite (Al2(PO4)(OH)):4-5H2O) andevansite

(Al3PO4(OH)6 6H2O). To date, at least 200 structure-types of open framework

AlPOs have been identified. These include neutral open framework AlPO4-n

molecular sieves, their isomorphous substitute analogues and anionic AlPOs

framework.

16

1.6.2 Synthetic AluminophosphateMolecular Sieves

The researchers at Union Carbide Corporation, USA discovered aluminophosphate materials, a novel class of crystalline microporous solids

that represents the first family of framework oxide molecular sieves

synthesized apart from the well knownaluminosilicates (zeolites) and silica molecular sieves (Flanigen 1976). The periodic table was viewed as potential

scope for new framework compositions and structures. This resulted in the

discovery of aluminophosphate molecular sieves as reported by Wilson et al (1982).

The family of aluminophosphate molecular sieves is microporous

crystalline oxides, many of which contain pores within their framework

structure like zeolites. In aluminophosphate molecular sieves (AlPO4) the

framework sites are occupied by Al3+ or P5+ and the average ionic radius of Al3+ (0.39 Å) and P5+ (0.17 Å) is 0.28 Å, which is very close to the ionic

radius of Si4+ (0.26 Å). The notable feature of AlPO4 composition is the

invariant Al2O3/P2O5 ratio which is in direct contrast to the variable compositions of SiO2/Al2O3 found in zeolite structures. Unlike zeolite

molecular sieves, which contain Al3+ and Si4+ in tetrahedral positions and

exhibit a net negative framework charge, aluminophosphate molecular sieves contain Al3+ and P5+ in tetrahedral position and the resultant framework is

neutral. Structural diversity is observed in AlPO4 materials even though there is only a limited variation in chemical composition.

The linkage of SiO4, AlO4, PO4 and other cationtetrahedra will decide the three dimensional framework shape and final structure type of the material. The structure of aluminophosphate molecular sieves contains 4-, 6-, 8- and 12- rings of alternating AlO4 and PO4tetrahedra. The avoidance of Al-O-Al and P-O-P bonds in aluminophosphate frameworks (Löwenstein’s rule) made their structures contain only even-numbered rings. Therefore zeolitic structures of pentasil family such as ZSM-5 and ZSM-11 were not

17

found in AlPOs. Table 1.4 presents five categories of these structures viz., very large pore, large pore, medium pore, small pore and very small pore groups.

1.6.3 Nomenclature

The aluminophosphate materials are classified into (i) binary, (ii) ternary, (iii) quaternary, (iv) quinary and (v) senary. The composition of aluminophosphate molecular sieves depends on the number of elements contained in the cationic framework sites of any given structure. The normalised TO2 formula represents the relative concentration offramework elements in the composition (ElxAlyPz)O2 where El is the incorporated element and x, y and z are the mole fractions of the respective elements in the composition. Acronyms describing the framework composition are shown in Table 1.5 (Flanigen et al 1986).The structure type is indicated by an integer following the compositional acronym, e.g. SAPO-5 is a (Si,Al,P)O2 composition with type 5 structure. The numbering of structure type is arbitrary and bears no relationship to structural numbers used previously in the literature, e.g. ZSM-5. It only identifies structures found in the aluminophosphate based molecular sieves. The same structure number is used for a common structure type with varying framework composition.

18

Table 1.4 Structure of aluminophosphate based molecular sieves

Species Structure type Ring size Pore size (Å) Very large pore VPI-5 novel 18 12AlPO-54 novel 18 12

Large pore

AlPO-5 novel 12 8 -36 novel 12 8 -37 faujasite 12 8 -40 novel 12 7 -46 novel 12 7Intermediate pore AlPO-11 novel 10 6.0 -31 novel 10 6.5 -41 novel 10 6.0Small pore AlPO-12 novel 8 4.0 -14 novel 8 4.0 -17 erionite 8 4.3 -18 novel 8 4.3 -34 chabazite 8 4.3 -35 levynite 8 4.3 -44 chabazite-like 8 4.3Very small pore AlPO-16 novel 6 3 -20 sodalite 6 3 -25 novel 6 3 -28 novel 6 3

19

Table 1.5 Acronyms for framework composition

TO2, T = Acronym

Al, P AlPO

Si, Al, P SAPO

Me, Al, P MeAPO

Mg, Al, P Zn, Al, P Co, Al, P Mn, Al, P

MAPO ZAPO

CoAPO MnAPO

Me, Al, P, Si Mn, Al, P, Si Mg, Al, P, Si Zn, Al, P, Si Co, Al, P, Si

MeAPSO MnAPSO

MASO ZnAPSO CoAPSO

Other elements El, Al, P El, Al, P, Si

ElAPO ElAPSO

20

1.7 STRUCTURAL ASPECTS OF ALUMINOPHOSPHATES

1.7.1 Classification

The open framework AlPOs reported to date comprise a wide range

of structures and compositions. In terms of electrostatic properties and

Al/P ratios of the frameworks, they can be classified into two major

categories viz.,(i) neutral framework AlPO4-n with Al/P = 1 and (ii) anionic

framework AlPOs with Al/P 1.

1.7.2 Neutral Framework

The characters of AlPO4-n include a neutral framework and a

univariant framework composition with Al/P = 1 (Bennett et al 1986).

Subsequent efforts to incorporate other elements led to the formation of

AlPO4-based molecular sieves such as SAPO (S: Si), ElAPO (El: Li, Be, B,

Ga, Ge, As, Ti, etc.), ElAPSO, MeAPO (Me: metal) and MeAPSO. Even

though some of them have not been found pure AlPO4-n counterpart yet, these

structures can be ideally described using a hypothetical AlPO4-n lattice with

alternate Al and P sites as the basis. The AlPO4-based molecular sieves

include 51 unique structure types withextra-large pores (>12-ring), large pores

(12-ring), intermediate pores (10-ring), small pores (8-ring) and very small

pores (6-ring). These structures include 16 zeolite analogues such as chabazite

(AlPO4-n = 34, 44 and 47), erionite (AlPO4-17), faujasite (AlPO4-37),

gismondine (AlPO4-43), levynite (AlPO4-35), linde type A (AlPO4-42),

sodalite (AlPO4-20) and 35 novel structures such as VFI (VPI-5), AEL

(AlPO4-11) and AFI (AlPO4-5). Figure 1.2 illustrates several representative

AlPO4-n molecular sieves with different pore openings and dimensions

including VPI-5 (VFI): 18-ring (1.27 × 1.27 nm), AlPO4-8 (AET): 14-ring

(0.79 x 0.87 nm), AlPO4-5 (AFI): 12-ring (0.73 x 0.73 nm), AlPO4-11 (AEL):

10-ring (0.40 × 0.65 nm), AlPO4-41 (AFO):10-ring (0.43 × 0.70 nm) and

21

AlPO4-25 (ATV): 8-ring (0.30 × 0.49 nm). Apart from aluminosilicate or

silica zeolites, AlPO4-based molecular sieves constitute a major class of

zeolitic materials. These AlPO4-based materials are normally stable upon

removal of the occluded template molecules and exhibit excellent thermal

stability up to 1000 ºC. These materials are mildly hydrophilic. The major

structures in the AlPO4-nmolecular sieves are listed in Table 1.6.

Figure 1.2 Representative AlPO4-n molecular sieves with different pore openings

22

Table 1.6 Structures of AlPO4-n molecular sieves

n IZAa structure code Pore diameter (nm)

(ring) Very Large Pore

8VPI-5

AET VFI

0.79 × 0.87 (14) 1.21 (18)

Large Pore 536374046

AFI ATS FAU AFR AFS

0.73 (12) 0.75 × 0.65 (12) 0.74 (12) 0.43 × 0.70 (10) 0.64 × 0.62 (12) 0.4 (8)

Intermediate Pore 113141

AEL ATO AFO

0.63 × 0.39 (10) 0.54 (12) 0.43 × 0.70 (10)

Small Pore 17183334353942434447

ERIAEI ATT CHALEV ATN LTA GIS

CHACHA

0.36 × 0.51 (8) 0.38 (8) 0.42 × 0.46 (10) 0.38 (8) 0.36 × 0.48 (8) 0.4 (8) 0.41 (8) 0.31 × 0.45 (8) 0.31 (8) 0.38 (8)

Very Small Pore 162025

AST SOD ATV

(6)(6)0.30 × 0.49 (8)

23

1.7.3 Anionic Framework AlPOs

In contrast to neutral framework AlPO4-n with Al/P = 1, most of

the anionic framework AlPOs have Al/P ratio less than unity (Yu &Xu 2003).

The structures of anionic AlPOs comprise three dimensional and low

dimensional frameworks made up of alternate Al-centered polyhedra (AlO4,

AlO5 and AlO6) and P-centered tetrahedra P(Ob)n(Ot)4-n (b = bridging,

t = terminal and n = 1,2,3 and 4) forming diverse stoichiometries. The

existence of terminal P–OH and/or P = O groups or Al(OP)n (n = 5 and 6)

polyhedra results in the deviation of Al/P ratio from unity in the framework.

Their Al/P ratios are found to 1/1, 1/2, 2/3, 3/4, 3/5, 4/5, 5/6, 11/12, 12/13,

13/18 and so on. Their frameworks exhibit fascinating structural architectures.

A notable example is JDF-20 with Al/P = 5/6 (Huo et al 1992), which has the

largest channel ring size of 20 among open framework AlPOs. Anionic

framework AlPOs have also been prepared with diverse low

dimensionalframework structures such as 2D layers with various porous

sheets and sheet stacking sequences and 1D chains which may act as

fundamental building blocks for complex structures. It is significant to note

that within each compositional family a wide variety of structure types have

been observed. For instance, the 2D frameworks with Al/P = 3/4 show diverse

layered structures. Most of the anionic framework AlPOs possess interrupted

open frameworks with terminal P–OH and/or P=O groups. They are unstable

upon removal of the occluded protonated template molecules by calcination.

1.7.4 Bonding Patterns

As that of zeolites, open-framework AlPOs made up of Al–O–P

bonds obey Löwenstein’s (1954) rule with avoidance of Al–O–Al bonds (only

one exceptional case was reported by Huang &Hwu (1999) in a layered AlPO

containing Al–O–Al linkages. The P–O–P bonds do not appear to be stable in

24

these structures. Thus the avoidance of Al–O–Al and P–O–P bonds endows

open-framework AlPOs featured by even-numbered rings.

In interrupted anionic frameworks, a part of Al–O–P linkages are missed and

terminal P–OH and/or P=O bonds are commonly observed that interact with

protonated templating molecules through H-bonds(Yu &Xu 2003). Using the

first-principle quantum chemical techniques, Cora&Catlow (2001)

characterized the bonding properties of crystalline AlPOs and compared them

with isostructural silica-based zeolites. Their calculation results revealed that

silica polymorphs and AlPOs differ in the nature of bonding. The silica

polymorphs consist of covalently bonded SiO4 units while AlPOs are shown

to be of molecular ionic character and comprised of discrete Al3+ and PO43-

ions. The ionicity of AlPO frameworks might be responsible for the major

contrast between the chemistry of AlPOs and that of aluminosilicates relative

to the nature and concentration of dopants that can be introduced into the

frameworks. In AlPOs, ionic substitutional dopants introduce minor

perturbations to the host electric structure and therefore more readily replace

Al in AlPOs than Si in zeolites.

1.8 TOPOLOGICAL CHEMISTRY OF ALUMINOPHOSPHATES

1.8.1 Building Units

The complex structures of open-framework AlPOs can be

understood on the basis of their construction from fundamental building units.

Topologically, the neutral framework AlPO4-n molecular sieves can be

described as four-connected 3D frameworks since Al and P atoms occupy the

4-connected vertices of 3D net. Most of the anionic framework AlPOs can be

described as interrupted frameworks because part of the Al-O-P linkages is

missed. The four connected 3D frameworks, typically for zeolite frameworks,

can be thought to be constructed of finite secondary building units (SBUs).

18 SBUs have been listed for zeolites in the fifth edition of the ATLAS

25

among which 8 occur in four-connected 3D AlPO4-n frameworks

(Figure 1.3). These SBUs are formed by primary building units (PBUs) of

AlO4 and PO4tetrahedra (known as TO4) by sharing a common oxygen atom

in their corners. Different linkages of these tetrahedral units lead to various

sheet topologies. Figure 1.4 shows eight distinct 2D sheet structures. These

SBUs are arranged in a specific geometrical pattern to form a definite crystal

structure and uniform pore size.

Figure 1.3 Secondary building units (SBUs) found in AlPO4-n based

framework

26

Figure 1.4 Eight distinct 2D sheet structures (The SBUs constructing

these sheets are also shown)

27

1.8.2 Al and P Coordinations and Stoichiometries

The structural and compositional richness of AlPOs are attributed to

the diverse coordination of Al and P atoms. The majority of AlPO4-n

molecular sieves are based on a four-connected network of corner sharing

tetrahedra, i.e., AlO4b and PO4b (b = bridging oxygen between Al and P).

There are a number of AlPO4-n with mixed-bonded frameworks containing

five orsix coordinated Al atoms with one or two extraframework oxygen

species such as OH and H2O (Chen et al 1999). For instance, both VPI-5 and

AlPO4-8 contain AlO4b (H2O)2 units; AlPO4-17, -18, -20, -21 and -31 contain

AlO4b(OH) units. By omitting the OH and H2O species, these frameworks can

be idealized as a four-connected framework. Combinations of alternate Al and

P atoms give rise to various framework structures and Al and P

stoichiometries. According to Löwensteinsrule, the number of Al–Ob bonds

must be equal to the number of P–Ob bonds in open framework AlPOs.

Consequently, the correlation of coordination environment of Al and P can be

described in the following equation (1.3) (Yu &Xu 2003).

AlOib AlOib POjb POjbi j

m i n j (1.3)

where i(j) is the number of bridging oxygen coordinated to Al(P), m(n) is the

number of AlOib (POjb) coordination, mAlOib nPOjb = Al/P, i = 3, 4, 5 and 6

corresponding to AlO3b, AlO4b, AlO5b and AlO6b units respectively, j = 1, 2, 3

and 4 corresponding to PO4 units with one, two, three and four bridging

oxygen respectively. Based on this equation, the detailed Al and P

coordination for a given stoichiometry can be enumerated.

28

1.9 TEMPLATING IN THE CONSTRUCTION OF

ALUMINOPHOSPHATES

Open framework AlPOs are synthesized by hydrothermal or

solvothermal crystallization of reactive aluminophosphate gels in the presence

of an organic base as the templating agent (or structure-directing agent) as in

the synthesis of high-silica zeolites. These template species occupy the pores

and cages of the structures and play an important role in directing the

formation of a specific structure.

1.9.1 Types of Templates

A large variety of organic templates can facilitate the synthesis of

open-framework AlPOs. So far, over 100 species have been used successfully

as templates, typically involving quaternary ammonium cations and various

organic amines including primary, secondary, tertiary and cyclic amines, and

alkanolamines. Some stable metal ligand complexes such as Cp2Co2+ and

Co(en)33+ have also been used in the synthesis of AlPO materials. Very

recently, ionic liquids have been used as both solvent and template for the

preparation of SIZ-n type AlPO materials (Cooper et al 2004 and Parnham

et al 2006). The one template multiple structure and multiple template one

structure phenomena are remarkable in open framework AlPOs. For example,

di-n-propylamine (Pr2NH) has been used in the synthesis of at least ten

different AlPO structure types such as AlPO4-11, -31, -39, -41, -43, -46, -47,

-50, H3/MCM-1 and H1/VPI-5/MCM-9, exhibiting low structure specificity.

On the other hand, some structures readily form from many different

templates, e.g., AlPO4-5 is much less template specific and can be synthesized

with more than 25 different templates. Few examples are given in Table 1.7.

Tetrapropylammonium hydroxide (TPAOH) is a typical template for the

synthesis of AlPO4-5, which is stacked in a tripod arrangement with the head

of one TPA ion suspended between three feet of the next TPA ion with a

29

hydroxyl group neatly suspended between them(Bennett et al 1986). As seen

in Figure 1.5, although this tripod arrangement is such a good geometrical fit

with the cylindrical wall, the TPAOH is not a template in the true sense

because of the inconsistency of the three fold molecular symmetry and six

fold channel symmetry.

Table 1.7Templates used for the preparation of specific structure type

Structure type Typical template(s)

AlPO4-5 tetrapropylammonium hydroxide, tripropylamine,triethylamine, etc.

AlPO4-11 dipropylamine, diisopropylamine

AlPO4-14 isopropylamine

AlPO4-17 quinuclidine, piperidine

AlPO4-18 tetraethylammonium hydroxide

AlPO4-20 tetramethylammonium hydroxide

AlPO4-31 dipropylamine

AlPO4-34 tetraethylammonium hydroxide

AlPO4-35 quinuclidine

AlPO4-36 tripropylamine

AlPO4-46 dipropylamine

AlPO4-47 dipropylamine and diethylethanolamine

30

Figure 1.5 Cylindrical channel in AlPO-5 and the stacking of

encapsulated tetrapropylammonium hydroxide species

A few AlPO structures exhibit high template specificity. For

example, AlPO4-20 can be crystallized only with tetramethylammonium

hydroxide (TMAOH). The spherical TMAOH molecule with 0.62 nm

diameter fits neatly into the sodalite cage. In some AlPOs, a mixture of

templates appears to cooperatively direct the formation of structures.For

instance, SAPO-37 is prepared by a mixture of TPAOH and TMAOH.

Structural characterization shows the presence of TMA in the sodalite cages

and TPA in the supercages. In the synthesis of AlPO4-52, both Pr3N and

TEAOH appear to be necessary but only TEAOH is occluded in the structure.

As with organic amine, water can also play an important structure directing

role. A notable example has been seen in VPI-5. Even though VPI-5 is

31

preferentially prepared in the presence of organic amines, the organic species

are not occluded into the extra large 18 ring pores. Instead, water molecules

form an intriguing H-bonded triple helix inside the channel(McCusker et al

1991).

1.9.2 Role of Templating

Templating has been a frequently discussed phenomenon in the

synthesis of zeolites and related open-framework materials (Davis &Lobo

1992 and Zones et al 1996). So far, the relationship between the templating

agents and the structures, usually known as templating effect, is still not fully

understood. The term templating has been frequently used in the context of

synthesizing high silica zeolites. One definition about templating was

described by Lok et al (1983) as the phenomenon occurring during either the

gelation or the nucleation process whereby the organic species organizes

oxide tetrahedra into a particular geometric topology around itself and thus

provides the initial building block for a particular structure type. The gel

chemistry is also essential for the formation of microporous

aluminophosphates. With the addition of organic base, the gel chemistry of

aluminophosphate is altered, and the templating becomes operative only in

the gel with right gel chemistry. Therefore the dual role of organic templates

in the synthesis of open framework AlPOs is evident. It serves the important

role of modifying the gel chemistry, and it also has a structure directing

effect.

The organic template plays at least two additional roles in the

product, i.e., stabilizing voids and balancing the framework charge. By

packing the cages and channels the organic template can increase the overall

thermodynamic stability of the template/lattice composite, so that the

metastablility of the lattice alone is less critical (Wilson 1991 and 2001). The

stabilizing and charge balancing role of organic templates is quite evident in

32

anionic framework AlPOs. After removing the occluded template molecules

by calcination, the anionic frameworks normally collapse. Furthermore, the

templates also determine the stacking sequences of 2D layers. The template

molecules interact with host inorganic network with certain regularity, and

their interaction can be well described based on the interaction between SBUs

and protonated amino groups. This allows the template molecules to be

located with a reasonable success.

Even though a true templating effect, i.e., hand in glove fit between

organic and inorganic lattice, is less pronounced in the synthesis of open

framework AlPOs, it seems that an encapsulated organic species in the void

space of the inorganic host can adopt configuration that conforms best with

the surrounding aluminophosphate framework. For example, AlPO4-12, -21

and -EN3 were synthesized with encapsulated ethylenediamine. It is stabilized

into optical isomers of the gauche form by intramolecular bonding in

AlPO4-12 and -21, while it occurs in AlPO4-EN3 as trans configuration with

N–C–C–N extended along a straight eight-ring channel. The empirical

evidence is that for a template to be successful there must be a good fit

between the guest molecule and the host framework formed. The importance

of template molecules appears not only in its role of structure directing but

also orientating the distribution of Si in the frameworks. Vomscheid et al

(1994) demonstrated the role of template in directing Si distribution in the

lattice of SAPO materials.

In metal-substituted AlPOs, the template molecules also influence the degree of metal ion substitution in the frameworks. Lewis et al (1996) studied the influence of organic templates on the structure and the concentration of framework metal ions in microporousAlPOs. Their calculations demonstrate that the degree of metal ion substitution in the framework is controlled not only by the relative stability of the framework but also by the need to accommodate the structure directing and charge

33

compensating template molecules. Templates with higher charge/size ratios will allow a greater control over the ratio of metal substitution or heteroatom incorporation in the framework.

1.10 ISOMORPHIC SUBSTITUTION

Apart from the structural similarity with zeolites, AlPO molecular sieves exhibit structural diversity due to their neutral framework in contrast to the negatively charged aluminosilicate. Secondly the aluminium atoms in the aluminosilicate framework are always tetrahedrally coordinated as compared to four, five or six coordinated aluminium atoms present in the AlPO framework as mentioned earlier in this chapter. Moreover, they also offer compositional diversity. The Al and/or P ions in the AlPO frameworks can be replaced by another element with similar cation radius and coordination environment. However, elements incorporated in the AlPO framework should possess radius ratios with oxygen, and T-O distances consistent with the applied crystal chemical concept for tetrahedral coordination. Their successful incorporation may be due to flexibility of microporousaluminophosphate framework and to specific interactions with organic template, coupled with mildly acidic gel chemistry used in the synthesis (Flanigen et al 1986).

Thus, the incorporation of silicon in aluminophosphate molecular sieves results silicoaluminophosphate, SAPO-n (Lok et al 1984). The addition of metal cations yield porous metal aluminophosphate, MeAPO-n or metalsilicoalumino phosphate, MeAPSO-n. In SAPO-n materials, silicon substitutes for phosphorous or for aluminium-phosphorous pair whereas metal cations substitute almost exclusively for aluminium. The MeAPO-n and MeAPSO-n materials encompass the characteristics of both zeolites and aluminophosphates which results in their unique catalytic, ion-exchange and adsorbent properties.

Flanigen et al (1988) reported framework incorporation of at least fifteen elements in the framework of aluminophosphate materials. The most

34

important of these cations are Si4+, Co2+, Zn2+, Mn2+, Mg2+, Cr6+, Ti4+ and V5+.It was suggested that successful incorporation of these elements is attributed to flexibility of the microporous framework and specific interactions with organic templates. The charge of the framework is balanced by template molecules in the as-synthesized materials and the charges in the calcined samples are compensated by H+ ions derived from the template. Thus Brönsted acidity generated in the neutral framework is as shown in Scheme 1.1. The strength of Brönsted acidity depends on the electronegativity of the element which is used for the isomorphous substitution.

Scheme 1.1 Generation of Brönsted acid sites in aluminophosphatemolecular sieves

When M2+ ions are substituted in the place of Al3+ ions, two units

of negative charge is generated in which one negative charge is balanced by

2+

Isomorphous substitution of M2+

Neutral AlPO

Isomorphous substitution of M4+

35

the positive charge on the P atom and other negative charge is balanced by H+

ion as shown in Scheme 1.1 (Lohse et al 1995). When M4+ ion substitute P5+

ion results a net negative charge on the Al atom and this is compensated by

protons derived from the template during calcination as shown in Scheme 1.1

(Prakash et al 1994).

1.10.1 Metal Aluminophosphates

Initially, Flanigen et al (1986) reported the incorporation of 13

elements into AlPO-5 including transition metal ions like titanium,

manganese, iron, cobalt and zinc. The incorporation of transition metal ions

into framework sites of aluminophosphate and silicoaluminophosphate

molecular sieves is also of particular interest for the design of novel catalysts.

Paramagnetic metal species are often introduced into the molecular sieves to

generate catalytically reactive species or site. Various pretreatment or

activation procedures are typically used to generate reactive metal ion valence

states which are often paramagnetic. Transition metal ions are incorporated by

three different methods viz., impregnation, ion-exchange and isomorphous

substitution. In the latter method the transition metal ion salt is incorporated

directly into the synthesis mixture. Since the comprehensive papers of

Flanigen et al (1986 and 1988) on aluminophosphates and the periodic table,

many studies have been published, claiming the isomorphous substitution of

transition metal ions into the framework of different structure types

(Hartmann &Kevan 1999).A variety of metals and transition metals can be

incorporated into aluminophosphate structure (Figure 1.6) but actual

incorporation into the tetrahedral framework is difficult to prove.

36

Figure 1.6 Partial periodic table with transition elements introduced intoaluminophosphates and silicoaluminophosphates

1.11 AlPO-5 MOLECULAR SIEVE

AlPO-5 is a microporousaluminophosphate. It consists of alternate

Al and P tetrahedra with cylindrical pores of diameter 0.73 nm. It possesses

hexagonal crystal symmetry with 24 tetrahedral oxide (TO2) units per unit

cell. The novel three dimensional structure of AlPO-5 was determined by

single crystal X-ray method (Bennett et al 1983). It has hexagonal symmetry

with a = 13.72 Å and c = 8.47 Å. It contains one dimensional channels

oriented parallel to the c axis bounded by 12-membered rings. The framework

structure of AlPO-5 is shown in Figure 1.7(Bennett et al 1983).It can be

synthesized with at least 24 different amines and quaternary ammonium

compounds as template. The drawback of AlPO-5 molecular sieve is neutral

and there is no acidity. Adsorption properties of AlPO-5 have been studied by

Stach et al (1986) and Lohse et al (1987) using hydrocarbon and water as

adsorbates.The incorporation of divalent metal ions in the framework of

AlPO-5 creates Brönsted acidity.

Ti V Cr Mn Fe Co Ni Cu Zn Zr Nb Mo Tc Ru Rh Pd Ag CdHf Ta W Re Os Ir Pt Au HgRf Ha

Framework incorporation

claimed

Ion-exchange and impregnation Not Studied

37

(a) (b) (c)

Figure 1.7 Framework topology of AlPO-5 (a) framework structure of AlPO-5, (b) 12-ring channel view along (001) plane and (c) 12-membered ring of AlPO-5

1.12 CATALYTIC APPLICATIONS OF MeAPO-5 MOLECULAR

SIEVES

The use of microporous solid catalysts such as zeolites and related

molecular sieves has an additional benefit in organic synthesis. The highly

precise organisation and discrimination between molecules by molecular

sieves endow them with shape selective properties, reminiscent of enzymatic

catalysts. The incorporation of transition metal ions and complexes into

molecular sieves extends their catalytic scope to redox reactions and a variety

of other transition metal catalysed processes (Sheldon & van Bekkum 2001).

The metal ion substituted aluminophosphate molecular sieves are

interesting as they possess more density of acid sites for catalytic applications.

Lin et al (1993) carried out one-step liquid phase oxidation of cyclohexane over

CoAPO-5 catalyst in the presence of glacial acetic acid as the solvent. Since

the conversion and selectivity reported in this study were moderately good

and hence CoAPO-5 was proved to be a useful catalyst for this reaction.

38

Concepcion et al (1997)carried out oxidative dehydrogenation of ethane over

MgVAPO-5 catalyst. This catalyst is very active and selective in this reaction.

The activity is related to the presence of Mg2+ in the framework of AlPO-5.

The low catalytic activity of VAPO-5 can be related to its lower reducibility.

Although catalysts with high vanadium or magnesium content could be

prepared, their low crystallinity could decrease the number of effective active

sites.

Suresh et al (2004) reported isopropylation of benzene with

2-propanol over alkaline earth metal substituted MeAPO-5 (Me = Mg, Ca, Sr

and Ba) molecular sieves. The selectivity of cumene and benzene conversion

are in the order: Mg >Ca>Sr>BaAPO-5. Among these catalysts,

MgAPO-5 is more active than other catalysts due to the presence of more acid

sites. Dumitriu et al (2002) reported trans-alkylation of toluene with

trimethylbenzenes over various MeAPO-5 catalysts. The activity of

MeAPO-5 catalysts follows the order:

SiAPO>MgAPO>MnAPO>ZnAPO>CoAPO which can be correlated with

acidic properties of the catalysts. The strength of acid sites of the catalyst

influences the competition among various reactions that occur during the

trans-alkylation process. Generally,

trans-alkylation or disproportionation reactions occur on strong acid sites

while isomerisation of xylenes predominates on weak acid sites.

Hentit et al (2007) investigated the alkylation of benzene and other

aromatics over AlPO-5, AlPO-11, FeAPO-5 and FeAPO-11 catalysts using

benzyl chloride as the alkylating agent. Among the catalysts FeAPO-5 and

FeAPO-11 showed both high activity and selectivity due to their pore size and

acidity. The activity of these catalysts for benzylation of different aromatic

compounds is in the following order: benzene > toluene >p-xylene > anisole.

The interesting observation is that this catalyst could be reused in the

39

benzylation of benzene for several times. Hsu and Cheng (1998) reported

pinacol rearrangement over V, Cr, Co, Cu, Ti and Zn substituted AlPO-5,

Fe substituted VPI-5, AlPO-11 and silicalite-1. Among the transition metal

ions substituted in the AFI crystal structure, Fe3+, Cu2+ and Ni2+ showed the

highest pinacol conversion and pinacolone selectivity. The catalytic activity

was found to exhibit no direct correlation with acid strength or amount of acid

sites in the catalysts. Besides, comparison of the catalytic activities of Fe-

substituted molecular sieves of different crystalline structures, the activity

decreased in the order: AlPO-5 > AlPO-l1 > AlPO-8 > VPI-5 > silicalite-1.

Since the catalytic activity is independent of pore diameter, the liquid phase

reaction is considered to proceed mainly on the outer surface of the catalysts.

The hydrophilicity of aluminophosphate surface is in favour of catalysing the

pinacol rearrangement.

Vijayaraghavan& Raj (2004) carried out vapour phase ethylation of

benzene with ethanol over AlPO-5, MgAPO-5, ZnAPO-5 and MnAPO-5.

MnAPO-5 was found to be more active than other catalysts. Although

isomorphic substitution in MnAPO-5 is nearly the same as in MgAPO-5 and

ZnAPO-5, the increased conversion over MnAPO-5 is attributed to the

presence of unpaired electrons in the d-subshell of manganese.

Elangovan&Murugesan (1997) studied the catalytic transformation

of cyclohexanol over AlPO-5, AlPO-11, SAPO-5, SAPO-11, VAPO-5,

VAPO-11, CoAPO-5, CoAPO-11, NiAPO-5, NiAPO-11, ZnAPO-5 and

ZnAPO-11. SAPO-5 and VAPO-5 were found to be more active than other

catalysts because of the presence of more number of acid sites. The product

distribution is influenced by acidity, weight hourly space velocity (WHSV)

and temperature. Kannan et al (1998) reported ethylation of toluene with

ethanol over NiAPO-5, NiAPO-11, ZnAPO-5 and ZnAPO-11 in the vapour

phase. The products formed in this reaction were ethyltoluene, diethylether,

40

benzene and styrene. The conversion was found to be maximumover ZnAPO-

5 at 350 ºC but further increase in temperature decreased the conversion due

to coke formation.

Oxidation of alkylbenzenes is a promising subject in industrial

chemistry. Many bulk chemicals such as terephthalic acid, phenol, benzoic

acid, etc., are manufactured by homogeneous liquid phase oxidation with

oxygen. The large scale liquid phase oxidation is the conversion of

p-xylene into terephthalic acid which is chiefly used as polyethylene

terephthalate polymer material. m-Xylene is also commercially oxidised to

isophthalic acid. Benzoic acid derived from the oxidation of toluene is an

important raw material in the production of various pharmaceuticals and

herbicides. Commercially cumenehydroperoxide and

ethylbenzenehydroperoxide are also manufactured by aerobic oxidation of

isopropyl benzene and ethylbenzene respectively (Ishii &Sakaguchi 2006).

Singh et al (1999) studied the oxidation of ethylbenzene over

MeAPO-11 (Me = Co, Mn or V). The excellent incorporation of metal into

the framework has been achieved by synthesizing MeAPO-11 in the presence

of fluoride ions. In spite of their large crystallite size, MeAPO-11s obtained

from fluoride route are more active in the oxidation of ethylbenzene. The

complete change in the oxidation state of vanadium from lower valence state

(IV) to higher valence state (V) during calcination is observed in VAPO-11.

The redox behaviour of MeAPO-11 has a potential influence on the catalytic

activity during the oxidation of ethylbenzene. VAPO-11, which has

significant redox behaviour, is most active.

Subrahmanyam et al (2002) studied the vapour phase oxidation of

toluene with molecular oxygen over CrAlPO. They reported that CrAlPO

functions both as acid and redox catalyst and observed that in CrAlPO both

acidity (due to Al3+) and redox properties (due to Cr5+/6+) are competing,

41

thus leading to benzene and benzaldehyde respectively. Subrahmanyam et al

(2004) also reported the aerial oxidation of cyclohexane over FeAlPO under

highpressure conditions and reported that the reaction is probably taking place

through radical initiated mechanism. Subrahmanyam et al (2005) studied the

oxidation of toluene over mesoporousVAlPO, and the productsbenzaldehyde

and benzoic acid were obtained when the oxidising agent was 70% TBHP

while with 30% H2O2 cresols were formed. The activity of VAlPO has been

compared with those obtained with other similar porous materials likeV-

MCM-48, V-MCM-41, V-Al-Beta and VS-1.

Potter et al (2012) reported simultaneous framework incorporation

ofheavy metal ions such as Ru(III) and Sn(IV) intoaluminophosphate

architectures and evaluated the catalytic activity in cyclohexene oxidation.

The bimetallic catalyst facilitated synergistic interactions, affordinghigh

degree of selectivity and activity in the catalytic oxidation reactions as

compared with their corresponding transition metal analogues (Co and Ti).

They also reported that heavy metal dopants suchas Ru and Sn in the

framework architecture displayed enhancedcatalytic turnovers compared to

their correspondingtransition metal analogues (such as Co and Ti) in

selectiveoxidation reactions. In particular, the bimetallic analogues ofthe

former exhibit a concomitant enhancement in catalyticactivity when

compared with the corresponding bimetallictransition metal counterparts,

suggesting a synergistic enhancementin catalytic properties.

Raboin et al (2012) reported the grafting of titanium alkoxide over

mesoporousaluminophosphate and evaluated the catalytic activity in the

liquid-phase epoxidation of cyclohexene in the presenceof TBHP. The

catalyst showed 67% selectivity to epoxide formation. Further, they compared

the catalytic properties with Ti grafted SBA-15 catalysts and reported that

both SBA-15 and mesoporousAlPO showed comparable activities and

42

selectivities in cyclohexene oxidation. In addition, Ti-AlPO catalysts

exhibited higher tendency towards allylic oxidationin comparison with similar

Ti-SBA15 catalysts.

Wang et al (2013) synthesized Pt-Co/AlPO-5 catalysts for the

preferential oxidation of CO in H2rich gases. The optimized catalysts were

highly active and selective.CO could be puri ed below 10 ppm in the reaction

temperature range of 110 –125°C under 1% CO, 1%O2, 12.5% CO2, 15%

H2O, 50% H2 in volume and N2 balance at the space velocity of 24,000 ml

gcat1h 1. Pt–Co/CoAPO-5 exhibited the best catalytic performance and Pt–

Co/AlPO-5 was the most active catalystat low reaction temperature, in which

particles of Pt–Co alloy were formed and the particles were highlydispersed

on the surface of the support.

Devika et al (2011) reported the single sited CeAlPO-5 catalyst for

the oxidation of ethylbenzene to acetophenone in air atmosphere. The

selectivity to acetophenone was above 90% at all reaction temperatures.

Devika et al (2012) reported the vapour phase oxidation of diphenylmethane

to benzophenone. They reported that not only active ceriumsite isolation is a

requirement for selective oxidation but also themagnetic field of cerium sites

and free radicals produced duringoxidation were also suggested to play a

major role in theselective oxidation. In addition, free rotation across the

phenyland ethyl carbon bond also key factor forselective oxidation of

diphenylmethane.

Smet et al (1998) reported Pr6O11-MoO3 catalysts for the selective

oxidation of isobutene to methacrolein. The synergism of Pr with Mo played

an important role in the oxidation. Rovira et al (2012) reported the catalytic

activity of ceria-praseodymia nanotubes in the CO oxidation. The

43

incorporation of Pr in CeO2lattice improved the redox properties, and their

nanostructure also aided the catalytic oxidation of CO

Praseodymium incorporated AlPO-5 (PrAlPO-5) with different

(Al+P)/Pr ratios were synthesized under hydrothermal condition in the

presence of fluoride ions. Similarly, iron incorporated AlPO-5 (FeAlPO-5)

with different Al/Fe ratios were also synthesized. It was found that fluoride

ions exhibited several rolessuch as (1) they solubilisealuminium in the

reaction mixture leading to slower nucleation, thus rendering the formation of

dense aluminophosphate phases less favourable, (2) they lead to slow crystal

growth rates yielding crystals of larger size with fewer defects and (3) the

fluoride ions impart a structure-directing and templating effect by interacting

with the framework. In this last role, fluoride ions behave as bidentate ligands

linking two aluminium ions. Consequently, the aluminophosphate framework

requires a cation to balance the charge. Generally, a protonated organic amine

is the counter ion.

General characterization was performed to check the purity and

crystalline nature of the desired phase, its surface area, morphology and

chemical composition. In depth spectroscopic techniques were employed to

understand the accessibility, redox ability, coordination, acidity and oxidation

state of the metal ions in PrAlPO-5 and FeAlPO-5 for specific catalytic

application. The characterization of the samples was performed using XRD,

BET, TEM, SEM and ICP-OES analysis. DRS-UV-Vis,ESR, XPS, 27Al, 31P

MAS NMR and ex-situ pyridine adsorbed IR were used to understand the

nature and surface chemistry of materials.

44

1.13 SCOPE AND OBJECTIVES OF THE PRESENT

INVESTIGATION

Synthesis of fine chemicals using homogeneous catalysts possess

several problems such as difficulty in separation and recovery, disposal of

spent catalyst, formation of undesirable and/or toxic wastes. Efforts have been

made to replace homogeneous catalysts by reusable and easily separable

heterogeneous solid acid catalysts for the synthesis of fine chemicals.

The incorporation of one or more transition metal ions into AlPO

framework has gained considerable importancebecause of their redox

behavior and potential bi-functionality (Lewis and Bronsted acid sites). A

wide array of amines was used as structure directing agents for the

preparation of microporousAlPOs. Among the various AlPOs, AlPO-5 has

been extensively studied structure.AlPO-5 is not template specific,it can be

synthesized using more than one template.

The main objectives of the present investigation are

Hydrothermal synthesis of AlPO-5 in fluoride medium using

aluminiumisopropoxide, orthophosphoric acid and hydrofluoric

acid as the sources for aluminium, phosphorous and fluoride

respectively.

Hydrothermal synthesis of PrAlPO-5 with (Al+P)/Prratios of

25, 50, 75, 100,150 and 200 in fluoride medium using

praseodymium nitrate hexahydrate as the source for

praseodymium. The synthesis procedure was similar to that of

AlPO-5.

45

Calcination of PrAlPO-5((Al+P)/Pr = 25, 50, 75, 100,150 and

200)in air atmosphere at 550 ºC to remove occluded

template.Physico-chemical characterization of the materials

using XRD, SAXS, DRS-UV-vis, BET, SEM, TEM, TPD-

NH3, TPR, FT-IR, ICP-OES, TGA, 27Al and 31P MAS-NMR,

ex-situ pyridine adsorbed IR, ESR and XPS.

Study of liquid phase aerobic oxidation of ethylbenzene over

calcined PrAlPO-5((Al+P)/Pr = 25, 50, 75 and 100) between

60 and 140 °C. Analysis of the product using gas

chromatograph (GC) and gas chromatograph coupled with

mass spectrometer (GC-MS).Study of the influence of

temperature, reaction time, (Al+P)/Pr ratios and substituents on

ethylbenzene conversion and product selectivity.Optimisation

of the reaction parameters for maximum conversion with high

product selectivity. Study of the stability and reusability of the

catalyst.

Study of campholenic aldehyde synthesis from -pinene over

bi-fuctional PrAlPO-5with (Al+P)/Prratios of 75, 100, 150 and

200 catalysts. Analysis of the product using gas chromatograph

(GC) and gas chromatograph coupled with mass spectrometer

(GC-MS). Study of the influence of temperature, reaction time,

solvent and (Al+P)/Pr ratios on -pinene conversion and

campholenic aldehyde selectivity, and optimisation of the

parameters for maximum conversion with high product

selectivity. Study of the stability and reusability of the

catalyst.Separation of the products of the reaction by column

chromatography. Identification of the structure of the isolated

product by 1H-NMR

46

Hydrothermal synthesis of FeAlPO-5 with Al/Fe ratios of 75,

100 and 150 in fluoride medium using iron (III) nitrate

nanohydrate as the source for iron (III).

Calcination of FeAlPO-5(Al/Fe = 75, 100 and 150) in air

atmosphere at 550 ºC to remove occluded template. Physico-

chemical characterization of the materials using XRD, DRS-

UV-vis, BET, SEM, TPD-NH3, ex-situ pyridine adsorbed IR,

ESR, XPS and ICP-OES.

Synthesis of 5-arylidene-2,4-thiazolidinedione over FeAlPO-5.

Study of the influence of temperature, reaction time, solvent

and Al/Fe ratios on 5-benzylidene-2,4-thiazolidinedione

synthesis, and optimization of reaction parameters. The

influence of various substituted benzaldehydes and

heterocyclic aldehydes as substrate in Knovenegal

condensation. The structural identification of isolated product

by 1H-NMR.

47

CHAPTER 2

EXPERIMENTAL METHODS

2.1 MATERIALS

2.1.1 Chemicals

Hydrothermal synthesis of MeAPO-5 (Me = Pr and Fe) was carried

out using triethylamine (Merck) as the organic template.

Aluminiumisopropoxide (Merck), orthophosphoric acid (Merck),

praseodymium nitrate hexahydrate (Indian rare earths Ltd.), iron (III) nitrate

nonahydrate (Merck) and hydrogen fluoride (Merck) were used as the sources

for aluminium, phosphorus, praseodymium, iron and fluoride respectively.

The other chemicals such asethylbenzene, toluene,diphenylmethane, 4-chloro-

1-ethylbenzene, 4-bromo-1-ethylbenzene,4-fluoro-1-ethylbenzene, 4-iodo-1-

ethylbenzene, 4-nitro-1-ethylbenzene, 4-nitro-1-methylbenzene, 4-methoxy-1-

ethylbenzene,4-methoxy-1-methylbenzene and -pineneof analytical grade

(Sigma Aldrich) were used to study the catalytic activity of calcined PrAlPO-

5.The chemicals such as 2,4-thiazolidinedione, benzaldehyde, 4-

methoxybenzaldehyde, 3-methoxybenzaldehyde, 4-nitrobenzaldehyde, 3-

nitrobenzaldehyde, 2-hydroxy-3-methoxybenzaldehyde, 2-nitrobenzaldehyde,

piperonal, thiophene-2-carbaldehyde and pyridine-3-carbaldehyde were of

analytical grade (Sigma Aldrich) used in the study of the catalytic activity of

calcined FeAlPO-5.Deionised water was used in the catalyst synthesis and

product extraction. Solvents such as chloroform, dichloroethane, acetonitrile,

acetone, dichloromethane, N,N-dimethylformamide, dimethylsulfoxide, water

and ethanol were of analytical grade (Merck). Ether and ethylacetate wereof

48

analytical grade (Merck) used in product extraction. All the chemicals were

used as such without any further purification. All the glassware used in all the

experiments were either Borosil or Vensil.

2.2 PREPARATION OF CATALYSTS

2.2.1 Synthesis of PrAlPO-5

Zhao et al (2006) reported the synthesis of CeAlPO-5 molecular

sieves. The same procedure was adopted tosynthesize PrAlPO-5 except the

crystallization time was extended to 12 h. PrAlPO-5 molecular sieves were

synthesized by hydrothermal crystallization of gel with the following molar

composition: xPr(NO3)3.6H2O: 1.0Al2O3: 1.3P2O5: 1.6TEA: 1.3HF:

425H2O.The typical synthesis procedure adopted is as follows:

Aluminiumisopropoxide (7.15 g, Merck) was soaked in 50 ml double distilled

water and aged for 24 h. In a polypropylene bottle praseodymium nitrate

hexahydrate (0.493 g, Indian rare earths Ltd.) was dissolved in ortho-

phosphoric acid (4.9 g, Merck), double distilled water (15 ml) and

triethylamine (2.8 g, Merck), and stirred for 2 h. This was labelled as solution

A. The aged aluminium precursor stirred for 2 h was added to solution A and

the resultant mixture was stirred for 2 h. This was labelled as solution B. Then,

hydrofluoric acid (0.98 g, Merck) diluted with 5 ml double distilled water was

slowly added to solution B and stirred for another 2 h. Finally, the gel was

transferred to a teflon lined stainless steel autoclave and heated at 180 °C for

12 h. The hot autoclave quenched in ice-cold water gave crystallized product

which was filtered and washed several times with water. The crystalline

product was dried in an air oven at 120 °C and calcined at 550 °C in air for 6

h at a heating rate of 1 °C min-1. The same procedure was adopted for the

synthesis of AlPO-5 without the precursor for praseodymium.

49

2.2.2 Synthesis of Praseodymium Oxide

Praseodymium nitrate hexahydrate (2.18 g) was dissolved in double

distilled water (20 ml) and then 5 ml aqueous ammonia solution was added to

it slowly with constant stirring. A pale greenish precipitate was formed, and

the stirring continued for another 2 h. The precipitate was filtered,

washed thoroughly with double distilled water and dried at 120 °C. The dried

sample was crushed well and calcined at 550 °C for 12 h at a heating rate of

1 °C min-1.

2.2.3 Synthesis of AlPO-5 Supported Pr6O11

AlPO-5 supported 3 wt% of Pr6O11 was prepared as follows:

AlPO-5 (1 g) was added to 50 ml aqueous solution of Pr(NO3)3·6H2O (0.3 g).

The reaction mixture was stirred at ambient temperature for about 24 h to

obtain dry powder. The dry powder was calcined at 550 °C for 6 h in air

atmosphere. This sample was used in the TPR and DRS-UV-Vis studies to

establish the absence of extra framework praseodymium species in PrAlPO-5.

2.2.4 Synthesis of FeAlPO-5

FeAlPO-5 was synthesized by hydrothermal crystallization of gel

with the following molar composition: xFe(NO3)3.9H2O: 1.0Al2O3: 1.3P2O5:

1.6TEA: 1.3HF: 425H2O.The typical synthesis procedure is as follows:

Aluminiumisopropoxide (14.3 g, Merck) was hydrolysed in 100 ml double

distilled water for 24 h. In a polypropylene bottle iron(III) nitrate nonahydrate

(0.23 g, Merck) was dissolved in ortho-phosphoric acid (9.8 g, Merck),

double distilled water (30 ml) and triethylamine (5.6 g, Merck), and stirred for

2 h. This was labelled as solution A. The hydrolysedaluminium precursor was

added to solution A and the resultant mixture was stirred for 3 h. This was

labelled as solution B. Then, hydrofluoric acid (1.96 g, Merck) diluted with

50

10 ml double distilled water was slowly added to solution B and stirred for

another 4 h. Finally, the gel was transferred to a teflon lined stainless steel

autoclave and heated at 180 °C for 12 h. The hot autoclave quenched in ice-

cold water gave crystallized product which was filtered and washed several

times with water. The crystalline product was dried in an air oven at 120 °C

and calcined at 550 °C at a heating rate of 1 °C min-1 in air for 6 h.

2.2.5 Synthesis of Fe2O3

Iron (III) nitrate nonahydrate (2.42 g) was dissolved in double

distilled water (20 ml) and then 2ml aqueous ammonia solution was added to

it slowly with constant stirring. A dark brown precipitate was formed, and

thiswas stirred continuously for another 2 h. The precipitate was filtered,

washed thoroughly with double distilled water and dried at 120 °C. The dried

sample was crushed well and calcined at 550 °C for 12 h at a heating rate of

1 °C min-1. This sample was used in the XRD studies to establish the absence

of extra framework iron species in FeAlPO-5.

2.3 CHARACTERIZATION OF SYNTHESIZED MATERIALS

The structural, physical and chemical characteristics of catalysts are

essential for deriving correlation between physico-chemical properties and

catalytic activities of the materials. Different methods were employed to

characterize the as-synthesized and calcinedmaterials. The following physico-

chemical characterization techniques have been adopted in thepresent study.

51

2.3.1 X-ray Diffraction (XRD)

The X-ray diffraction (XRD) patterns were mainly used to identify

the structure, crystallographic phase present in the catalyst, degree of

crystallinity, unitcell parameter and crystallite size of the catalysts.

The conventional X-ray source consists of a target which is

bombarded with high energy electrons. Commonly CuK , CoK , FeK and

MoK are used as the sources for X-ray. Usually CuK radiation with an energy

of 8.04 keV and a wavelength of 0.154 nm was used as the source for X-ray.

The X-ray diffraction method involves the interaction between incident

monochromatised X-ray and atoms of periodic lattice. X-rays scattered by

atoms in an ordered lattice interfere constructively in the directions given by

Bragg’s law in Equation (2.1) (Bragg & Bragg 1949)

dSin2n (2.1)

where n = 1,2,3,… is the order of reflection, is the wavelength of X-rays,

d is the distance between two lattice planes and is the Bragg’s angle. This

law relates the wavelength of electromagnetic radiation to the diffraction

angle and the lattice spacing in a crystalline sample. Crystal structures

produce several thousand unique reflections, whose special arrangement is

referred as diffraction pattern. Indices (hkl) may be assigned to each reflection,

indicating its position within the diffraction pattern. The pattern has a

reciprocal Fourier transform relationship to the crystalline lattice and the unit

cell in the real space.

X-ray diffractograms revealedimportant and useful information

about a solid sample.

52

Whether the solid scanned is crystalline or amorphous in

nature.

Kinetics of the crystallization of a material during synthesis.

Presence of impurity phase can be identified by finger print

matching of a known sample with synthesized sample.

Changes in shape and size of unit cell with respect to the

position ofthe peak in a XRD profile.

Crystallite size (D) can be determined from the corrected line

broadening ( ) in a solid sample using Scherrer Equation (2.2)

D =K / Cos (2.2)

where D is the crystal size of the catalyst, is the X-ray wavelength (1.54 Å),

is the full width at half maximum (FWHM) of the sample, K is a

constant(equal to 0.89) and is the Bragg’s angle.

The XRD patternsof PrAlPO-5 and FeAlPO-5 wererecordedon a X-

ray diffractometer (PANalytical X’ Pert Pro) using CuK =1.54 Å) radiation

and liquid nitrogen-cooled germanium solid-state detector. The

diffractograms were recorded in the 2 range 5-80° in steps of 0.02° with a

count time of 5 s at each point. The small angle X-ray diffraction pattern of

PrAlPO-5 was recorded on a Bruker D8 advanced powder X-ray

diffractometer using CuK ( =1.5418 Å) as the radiation source. The

diffractograms were recorded in the 2 range 0.5-6o with a step size of 0.01o

and a step time of 1s at each point.

53

2.3.2 Diffuse Reflectance Ultraviolet - Visible Spectroscopy

Diffuse reflectance ultraviolet - visible spectroscopy

(DRS-UV-Vis) is known to be a very sensitive and useful technique for the

identification and characterization of metal ion coordination and its existence

in the framework or extra-framework position of a metal containing molecular

sieves. It deals with the study of electronic transitions between orbitals and

bands of atoms, ions or molecules in gaseous, liquid and solid state. This

technique is based on the reflection of light in the ultraviolet (UV) and visible

(vis) region by a powdered sample. The DRS-UV-Vis absorption spectra were

recorded using UV-Vis. spectrophotometer (Shimadzu model 2450) with

BaSO4 as the standard for measurements in the scan range of 190-900 nm.

The thickness of the quartz optical cell was 5 mm. The absorption intensity

was expressed as the Schuster-Kubelka-Munk function, F(R ) = (1- R )2/

2R , where R is the diffuse reflectance (DR) of a semi-infinitive layer and

F(R ) is proportional to the absorption coefficient.

2.3.3 Nitrogen Sorption Studies

Surface area measurement of solid materials is an important

parameter in catalyst characterization. Measurement of the quantity of

nitrogen adsorbed on a solid surface at a constant temperature with varying

adsorbate pressure has been studied extensively by many researchers

(Brunauer et al 1938, Barret et al 1951, Sing et al 1985). The Brunauer-

Emmett-Teller (BET) volumetric gas adsorption technique using N2 or Ar is

the standard method for the determination of surface area of a finely divided

porous material. The relationship between the amount of N2 adsorbed and

equilibrium pressure of the gas at a constant temperature is defined as the

adsorption isotherm. The specific surface area of a sample was calculated

using Brunauer-Emmett-Teller (BET) equation (2.3).

54

o m m o

p 1 C 1 pV(p p) V C V C p

(2.3)

where Vm is the volume of the gas forming monolayer on the adsorbent at

standard temperature and pressure (STP), p is the pressure at which volume

(V) of the gas is adsorbed, po is the saturated vapour pressure of the gas and C

is a constant.

The specific surface area, specific pore volume and average pore

diameter (BJH method) of the samples were determined by nitrogen

adsorption-desorption isotherms at 77 K using Belsorb mini II sorption

analyser. All the samples (50 mg) were degassed for 3 h at 250 °C under

vacuum (10-5 mbar) in the degas port of the adsorption analyser. Helium was

used as the carrier gas and thermal conductivity detector (TCD) as the

detector. Pore size was mapped directly from nitrogen adsorption isotherms

along with surface area of the catalyst. The same measurements were also

determined using Micromeritics ASAP 2020volumetric adsorption analyser.

The plot of )pV(p

p

o versus

opp gave a straight line with the

slope =m

C 1V C

. From the slope and intercept, Vm was derived. Then the number

of molecules of nitrogen adsorbed was calculated using equation (2.4).

Number of molecules of nitrogen adsorbed =V X 6.023 X 10

0.0224 (2.4)

The specific surface area (S) was obtained by multiplying the same with

cross-sectional area of nitrogen molecule, which is taken as 16.2 10-20 m2 as

shown in equation (2.5).

55

0224.0102.16V10023.6(S)areasurfaceSpecific

20m

23

(2.5)

The total surface area (St) of the sample was obtained using the following

equations (2.6 - 2.8).

t m csS n A N (2.6)

MWn m

m (2.7)

MNAWS csm

t (2.8)

where N is the Avogadro number (6.023 × 1023 molecules mol-1), M is the

molecular weight of the adsorbate, Wm is the weight of the adsorbate

constituting a monolayer surface coverage, nm is the amount adsorbed

constituting a monolayer surface coverage and Acs is the molecular cross-

sectional area of the adsorbate molecule. The specific surface area (S) of the

solid was calculated from the total surface area (St) and the degassed sample

weight (m) using the equation (2.9).

mSS t (2.9)

The total pore volume was calculated by converting the volume of

nitrogen adsorbed (Vads) into volume of liquid nitrogen (Vliq) using the

equation (2.10).

ads mliq

PV VVRT

(2.10)

56

where P and T are the ambient pressure and temperature respectively. Specific

pore volume (Vp) was calculated from equation (2.11).

mV

V liqp (2.11)

where m is the weight of adsorbent after degassing.

2.3.4 Fourier Transform - Infrared (FT-IR)Spectroscopy

Fourier transform infrared spectroscopy (FT-IR) is a

multidisciplinary analytical tool, which gives information pertaining to the

structural details of a material. In addition, it can be used to confirm surface

characteristics such as acidity and isomorphous substitution by other elements

in the material. FT-IR involves the absorption of electromagnetic radiation in

the infrared region of the spectrum which results changes in the vibrational

energy of a molecule. It is a valuable and formidable tool in identifying

organic compounds which have polar chemical bonds such as OH, NH, CH,

etc., with good charge separation. Since every functional group has unique

vibrational energy, the IR spectra can be seen as their fingerprints. IR spectra

of calcined samples were recorded on a FT-IR spectrometer (Perkin

Elmer,Spectrum Two) by ATR sampling technique (Figure 2.1).

Figure 2.1 Schematic diagram of multiple reflection ATR system

57

ATR uses a property of total internal reflection resulting in an

evanescent wave. A beam of infrared light is passed through the ATR crystal

in such a way that it reflects at least once off the internal surface in contact

with the sample. This reflection forms the evanescent wave which extends

into the sample. The penetration depth into the sample is typically between

0.5 and 2 micrometres, with the exact value being determined by the

wavelength of light, the angle of incidence, the indices of refraction for the

ATR crystal and the medium being probed. The number of reflections may be

varied by varying the angle of incidence. The beam is then collected by a

detector as it exits the crystal. In horizontal ATR (HATR) units, the crystal is

parallel sided plate, typically about 5 cm by 1cm, with the upper surface

exposed. The number of reflections at each surface of the crystal is usually

between five and ten, depending on the length and thickness of the crystal and

the angle of incidence.

2.3.5 Thermogravimetric Analysis (TGA)

In thermoanalytical technique, the change in sample weight is

measured while the sample is heated at a constant rate under air or nitrogen

atmosphere. This technique is effective for quantitative analysis of thermal

reactions that are accompanied by mass changes due to evaporation,

decomposition, gas adsorption, desorption and dehydration.

Thermogravimetric analysis (TGA) is widely used to study the structural

stability of molecular sieves. It provides information about the temperature

range required for expulsion of adsorbed water, decomposition of occluded

organic cations, structural modification and phase changes in the pores of

molecular sieves. The sample and reference material are simultaneously

heated or cooled at a constant rate. Reaction or transition temperatures are

then measured as a function of temperature difference between the sample and

the reference. It provides vital information about the materials with respect

58

totheir endothermic and exothermic behaviour at high temperatures. TGA of

the materials was performed (Perkin Elmer SII Diamond series) with 10 mg

of the sample under N2 atmosphere at a heating rate of 10 °Cmin-1 in the

temperature range 30-900 ºC.

2.3.6 Temperature Programmed Desorption (TPD)

The very common method applied to detect the presence of acid -

OH groups (Si-OH-Al groups or bridging -OH groups) is the temperature

programmed desorption (TPD) using basic gases such as ammonia and

pyridine with molecular size smaller than the pore size as probe molecule.

Due to their small molecular dimensions, pyridine and ammonia are suitable

to probe all -OH groups accessible in the pores, channels or windows of size

4 Å. Depending upon the number and strength of acid sites distributed on

the surface of the catalysts both its activity and selectivity vary. With proper

understanding of the acidic property requirement for various reactions,

catalysts with high activity and selectivity can be designed. In the TPD

method, desorption rate of pre-adsorbed base is continuously measured by

heating the catalyst in an inert gas stream of helium or nitrogen. The desorbed

amount of ammonia gave information about the number of -OH groups.

The quantitative analysis of the characteristic desorption curve

provides information about the strength and distribution of acid sites. The

strength and number of acid sites of PrAlPO-5 and FeAlPO-5were determined

by TPD of ammonia using Micrometrics Chemisorb 2750 pulse

chemisorption system. Approximately 50 mg of the sample was placed in a

U-shaped, flow-through, quartz tube. The surface of the sample was cleaned

by heating the sample at 250 C for 30 min with helium flow of 20 ml min-1.

The sample was then cooled to 100 C and saturated with 10% NH3-He

mixture. Then, isothermal desorption of ammonia from dead volume and

59

physically adsorbed ammonia were carried out in a flow of helium for 20

min.The temperature programmed desorption (10 oC min-1) of the sample was

recorded in the temperature range of 100 – 600 oC at a heating rate of 5 C

min-1under helium atmosphere. Ammonia molecules desorbed at low

temperature are weakly bound to the active sites and those desorbed at high

temperature are due to strong chemisorption on the active sites.

2.3.7 Temperature Programmed Reduction (TPR)

Temperature-programmed reduction (TPR) is yet another

technique used for the characterization of solid materials. It is often used in

the field of heterogeneous catalysis to find the most efficient reduction

conditions. The oxidized catalyst precursor is subjected to a programmed

temperature rise while a reducing gas mixture is flowed over it. Temperature-

programmed reduction (TPR) determines the number of reducible species

present on the catalyst surface and reveals the temperature at which the

reduction of each species occurs. The important aspect of TPR analysis is that

the sample need not possess any special characteristics other than the

presence of reducible metals.

Temperature programmed reduction (TPR) experiments were

carried out using a Micromeritics Chemisorb 2750. The reactor was a

U-shaped quartz tube and the sample was held in position by quartz wool

plugs. Prior to the TPR experiment, the reactor and its contents were flushed

with argon gas at a flow rate of 30 ml min-1 under controlled heating upto

150 °C, and then held isothermal for 30 minutes. The inert gas was then

switched over to a 10% H2/Ar mixture and the reduction was performed at a

controlled heating rate of 10 °C min-1 from 150to 900 °C. The hydrogen

consumption was monitored by a thermal conductivity detector (TCD).

60

2.3.8 Scanning Electron Microscopy (SEM)

Scanning electron microscopy (SEM) is one of the most widely

used techniques for the characterization of size and morphology of the

materials. SEM provides not only topographical information like optical

microscopes but also information pertaining to chemical composition near the

surface. SEM creates magnified images by using electrons instead of light.

It gives detailed 3D images at higher magnification than an optical

microscope. The various processes of interaction of primary electron beam

with catalysts in an electron microscope are shown in Figure 2.2. In the

scanning electron microscope, back scattered electrons and secondary

electrons are captured by a detector to form the image.

Figure 2.2 Theinteraction between primary electron beam and the sample in an electron microscope

Secondary electrons arise due to inelastic collision between primary

electrons (the beam) and loosely bound electrons of the conduction band or

tightly bound valence electrons. The energy transferred is sufficient to

overcome the work function which binds them to the solid and they are

ejected. The ejected electrons possess 5to10 eV energy and they are detected

by scintillator/photomultiplier tube. Back scattered electrons arise due to

e-

Sample

Unscattered electrons

Elastically scattered electrons

Interaction volume

Back scattered electrons

Auger electronsSecondary electrons

Inelastically scattered electrons

Incident electron beam

61

elastic collisions between the incoming electron and the nucleus of the target

atom (i.e. Rutherford scattering). Higher the atomic number, higher is the

number of back scattered electrons. They are detected by semiconductor

detectors. Most of the catalysts used in the present study are low conducting

specimens and hence the catalysts were coated with gold by sputtering

method. The morphology of the materials were recorded using a scanning

electron microscope (Hitachi-S-3400N) operated at an accelerating voltage of

16 kV. The samples were suspended in methanol and the specimen stub was

dipped into the liquid and removed.The sample powder deposited onto the

surface of the stub evenly when methanol was evaporated. Thisspecimen was

coated with gold for two minutes. The beam is scanned over the specimen

surface in synchronism with the beam of a cathode ray tube (CRT) display

screen. Materials can be studied properly only when they are electrically

conducting otherwise they give rise to charging phenomenon resulting blurred

images.

2.3.9 Transmission Electron Microscopy (TEM)

Transmission electron microscopy (TEM) has been extensively

used for determination of the size of nanoparticles. The electron gun consists

of a tungsten anode, an accelerating anode and a beam aperture control. An

electron lens system focuses the electron beam with very narrow cross section

at the point where it strikes the specimen. The transmitted electrons pass

through another set of electronic optics to finally fall on a fluorescent screen

where the image is produced, and recorded on a photographic film. TEM uses

transmitted electrons such as unscattered, elastically scattered and

inelastically scattered electrons. The use of high energy electrons (100 keV or

more) gives high resolution and reduces chromatic aberration. The resolution

of commercial instruments is 1 nm and the magnification is about 106 times

higher than ordinary optical microscope.

62

Transmission electron microscopic (TEM) images were recorded

using a JEOL TEM-3010 electron microscope operated at an accelerating

voltage of 300 keV. The samples for TEM analysis were prepared by

dispersion of the catalysts in ethanol under sonication and deposited on a

copper grid.

2.3.10 X-ray Photoelectron Spectroscopy (XPS)

The typical X-ray photoelectron spectrum (XPS) represents the plot of number of electrons detected versus binding energy (BE) of the electrons

detected. Each element produces a characteristic set of XPS peaks at

characteristic binding energy values that directly identify each element that exist in or on the surface of the material being analyzed. These characteristic

peaks correspond to the electronic configuration of the electrons within the

atoms. The number of detected electrons in each of the characteristic peak is

directly related to the amount of element within the area (volume) irradiated.

To generate atomic percentage values, each raw XPS signal must be corrected by dividing its signal intensity by a relative sensitivity factor (RSF) and

normalised over all the elements detected. To count the number of electrons at

each BE value, with the minimum error, XPS must be performed under

ultra-high vacuum (UHV) condition because electron counting detector in

XPS instrument is typically one meter away from the material irradiated with

X-rays. The main components of a XPS system include a source for X-rays,

an ultra-high vacuum stainless steel chamber with UHV pumps, an electron

collection lens, an electron energy analyzer, a magnetic field shielding, an

electron detector system, sample mounts and stage.

XPS is used to determine

Elements present in a sample and quantity of elements present

within approximately 10 nm of the sample surface.

63

Existence of very small contamination on the surface or in the bulk of the sample.

Empirical formula of a material which is free of excessive

surface contamination.

Identification of the chemical state of one or more elements in

the sample.

Binding energy of one or more electronic states.

Thickness of one or more thin layers (1 - 8 nm) of different

materials within the top 10 nm of the surface.

Density of electronic states.

The X-ray photoelectron spectrum was recorded on a Thermo

Multilab 2000 using monochrome AlK radiation as the excitation source.

Prior to analysis, the sample was evacuated under high vacuum and then

introduced into the analysis chamber. The spectra were recorded for Pr3d, O1s,

Al2p and P2p photoelectron peaks in PrAlPO-5 and Fe2p, O1s, Al2p and P2p in

FeAlPO-5. Each spectral region of photoelectron was scanned several times

to obtain good signal-to-noise ratios.The powder samples were fixed on a

steel holder with double-face adhesive tape and analysed as received. An

electron flood gun was used to reduce the charge effects.

2.3.11 Electron Spin Resonance (ESR) Spectroscopy

ESR technique is very sensitive to environmental symmetry of

transition metal cations as long as they are paramagnetic. The coordination

environment of praseodymium in PrAPO-5 and iron in FeAlPO-5 samples

were confirmed by this technique. The ESR spectrum was recorded on a

Bruker EMX Plus spectrometer at room temperature with microwave power

64

of 0.632 mW and modulation frequency of 100 kHz. The sample (40 mg) was

taken in a quartz tube with 4 mm outer diameter and then evacuated to

approximately 10-3 Torr. The tube was sealed under vacuum and then set in a

quartz Dewar vessel fitted in the EPR cavity.

2.3.12 Magic Angle Spinning - Nuclear Magnetic Resonance

(MAS-NMR) Spectroscopy

High resolution NMR will be of comparatively little value in the

catalyst field because broad lines observed in solids tend to obscure the shifts

of the resonance line. In powdered solids, chemical shifts and scalar

J couplings are largely hidden because of the presence of large anisotropic

interactions like dipolar couplings and chemical shift anisotropies, which lead

to significant broadening of the signals. Both the chemical shifts Hamiltonian

and the dipolar coupling Hamiltonian depend on the orientation of the

molecule with respect to the direction of the external field. Powdered solids

contain many crystallites with random orientation. The anisotropic

interactions thus lead to broad patterns since different molecular orientations

present in the sample give rise to different spectral frequencies. The resulting

lack of resolution obscures information contained in the spectrum. It is thus

necessary to apply special techniques to obtain high resolution spectra. This is

a major contrast with liquid state NMR, for which fast tumbling of molecules

causes anisotropic interactions to average themselves to isotropic values

resulting sharp lines.

Solid state MAS-NMR is a powerful tool in the structural analysis

of zeolites and zeo-types especially for obtaining information of local

structure, geometry and coordination of the building atoms such as Al and P

or the heteroatoms substituted. The anisotropic broadening was averaged to

zero when the sample physically rotates around = 54.74°. This angle is

65

referred to as magic angle ( m) since the resulting spectrum has similar

narrow lines characteristics to a liquid state spectrum. The associated

technique known as magic angle spinning (MAS) has been extensively used

in solid state NMR experiments with spinning rates routinely set in the range

of 10 - 30 kHz and up to 70 kHz. When the sample is spun around the magic

angle at a rate faster than the anisotropy of interaction, all the crystallites

appear to exhibit the same orientation. At the magic angle the chemical shift

anisotropy and the dipolar interactions are averaged to zero and thus reduction

of line broadening is observed.

Detailed information may thus be derived on the structure of a

catalyst, its thermal or chemical transformation, specific sorbent-sorbate

interactions, nature of chemically deposited species, catalytically active sites

and chemical reactions at the catalyst. 27Al MAS-NMR spectrum

quantitatively distinguishes between four and six coordinated aluminium

sites. The nature of interaction between aluminium and phosphorus is

obtained from 31P MAS-NMR spectroscopy. Solid state 27Al MAS-NMR and 31P MAS-NMR spectra of PrAlPO-5 sample were recorded on a Bruker NMR

spectrometer at 5 kHz. Solid state 27Al and 31P chemical shifts were externally

referenced to [Al(H2O)6]3+ in aqueous Al(NO3)3 and H3PO4(85 wt% in water)

respectively.

2.3.13 Inductively Coupled Plasma - Optical Emission Spectroscopy

(ICP-OES)

Chemical analysis was performed with ICP-AES Perkin Elmer

OPTIMA 5300 DV ICP-OES instrument. About 0.25 g of dried sample was

accurately weighed in a platinum crucible. The crucible was heated in an

electrical Bunsen burner to red-hot for 3 h and from the weight loss of the

material, the percentage of the volatile matter was calculated. To this sample,

66

5 ml of concentrated hydrochloric acid was added. It was stirred and the clean

solution was made up to 100 ml in a standard flask with double distilled water.

The aluminium,iron and praseodymium contents in the solution were then

determined using ICP-OES instrument.

2.4 CATALYTIC STUDIES

2.4.1 Liquid Phase Reactions

The reaction was carried out in liquid phase in a batch reactor

consisting of a double- necked round bottom flask fitted with a condenser.

The reactants and the respective catalyst were taken in a round bottom flask

of desired volume fitted with a reflux condenser. The flask with its content

kept inside an oil bath was heated at a constant temperature while being

stirred magnetically. The temperature of the oil bath was controlled using a

thermocouple. The progress of the reaction was monitored using the clear

centrifugate obtained by centrifuging the aliquots withdrawn from the hot

reaction mixture at regular intervals. The schematic diagram of the reactor

set-up is depicted in Figure 2.3.

67

Figure 2.3 Catalytic reaction set up for liquid phase reactions

68

2.4.1.1 Oxidation of ethylbenzene

PrAlPO-5 (200 mg) and ethylbenzene (50 mmol) were taken in a

two necked round bottom flask fitted with a condenser and a magnetic pellet

for stirring. To this heterogeneous reaction mixture, air was purged through a

balloon for 6 h. After completion of the reaction, the reaction mixture was

filtered and washed the catalyst with ether for 5 to 6 times. The filtrate was

poured into ice cold water and extracted with ether. The ether layer and

washings were combined and dried over anhydrous sodium sulphate. The

ether layer was evaporated to obtain the product.The products were analyzed

as given in section 2.5.

2.4.1.2 Synthesis of campholenic aldehyde from -pinene

PrAlPO-5 (100 mg), -pinene (5 mmol) and chloroform (10 ml)

were taken in a three necked round bottom flask (50 ml) fitted with a

condenser and a magnetic pellet was placed for stirring. To this heterogeneous

reaction mixture, air was purged through an aerator maintained at a flow rate

of 5 ml min-1 for 12 h. After completion of reaction, the reaction mixture was

filtered and washed the catalyst with ether. The filtrate was poured into ice

cold water and extracted with ether. The ether layer and washings were

combined and dried over anhydrous sodium sulphate. The ether layer was

evaporated to obtain the product. The products were analysed as given in

section 2.5. The structure of the major product was confirmed by 1H-NMR

spectrum.

2.4.1.3 Synthesis of 5-arylidene-2,4-thiazolidenedione

FeAlPO-5 (100 mg),2, 4-thiazolidinedione (5 mmol), aldehyde (5mmol),

water (4 ml) and ethanol (1 ml) were taken in a two necked round bottom flask (50

69

ml) fitted with a condenser. A magnetic pellet was placedinside the flask for stirring

(500 rpm) content in the flask. The reaction mixture was refluxed for an appropriate

time and then filtered. The progress of the reaction was monitored with TLC under

UV light. When the reaction was completed, product was filtered along with the

catalyst. The precipitate was washed with water and dissolved in ethyl acetate to

separate the catalyst. The organic layer was evaporated and crude product was

column purified using silica gel of 60-120 mesh with hexane-ethyl acetate as eluent.

The structure of the product was confirmed by 1H-NMR.

2.5 PRODUCT ANALYSIS

Quantitative analysis of the liquid products of the reactions was

carried out using a gas chromatograph (GC). The products were also

confirmed using a gas chromatograph coupled with a mass spectrometer.

The details of the product analysis using GC and GC-MS are given in the

following sections.

2.5.1 Gas Chromatograph

Quantitative analysis of the reaction products were carried out

using a gas chromatograph (GC; Shimadzu GC-17A) with DB-5 capillary

column (30 m x0.25 mm x 0.25 m) equipped with a flame ionisation detector

(FID). Nitrogen was used as the carrier gas. The oven temperature was fixed

at 70 °C and the column temperature was in the range of 100 - 250 °C at a

heating rate of 10 °Cmin-1. The sample (5 L) was injected in the injection

port and the gaseous sample travelled and separated in the column through an

oven and finally reached the flame ionisation detector (FID).

The conversion of reactant and selectivity of the products were calculated

from GC analysis.

70

2.5.2 Gas Chromatograph Coupled with Mass Spectrometer

The reaction products were also confirmed using a gas

chromatograph (Perkin-Elmer Clarus 500 Auto System XL with elite series

PE-5 capillary column, 30 m x 0.25 mm x1 m) coupled with a mass

spectrometer (GC-MS) (Turbo; EI, 70 eV). DB-1 (100%

dimethylpolysiloxane) column and helium was used as the carrier gas at a

flow rate of 1 mlmin-1. Each component of the product mixture was identified

from its characteristic m/e value and fragmentation pattern.

2.5.3 NMR Spectroscopic Analysis

The NMR spectrum proves to be of great utility in structure

elucidation because the properties it displays can be related to the chemist's

perception of molecular structure. The chemical shift of a particular nucleus

can be correlated with its chemical environment, the scalar coupling (or J-

coupling) indicates an indirect interaction between individual nuclei,

mediated by electrons in a chemical bond, and under suitable conditions, the

area of a resonance is related to the number of nuclei giving rise to it.

The 1H nucleus is the most commonly observed nucleus in NMR

spectroscopy. Hydrogen is found throughout most organic molecules and,

fortunately for chemists, the proton has high intrinsic sensitivity as well as

being almost 100% abundant in nature, all of which make it a favourable

nucleus to observe. The proton NMR spectrum contains a wealth of chemical

shift and coupling information and is the starting point for most structure

determinations. The structure of the products isolated in the synthesis of

campholenic aldehyde and 2,4-thiazolidinedione analogues were elucidated

by 1H-NMR. The sample was dissolved in appropriate deutrated solvent

(CDCl3 or DMSO-d6) and 1H-NMR spectrum was recorded on a Bruker AV

III 500 MHz FT NMR spectrometer.

71

CHAPTER 3

PHYSICO-CHEMICAL CHARACTERIZATION OF

PrAlPO-5 and FeAlPO-5 MOLECULAR SIEVES

3.1 INTRODUCTION

The substitution of Al by metal ions could generate Brønsted acid

sites (bridging OH groups) as well as Lewis acid sites (corresponding to

anionic vacancies deriving from missing lattice oxygens) in the

aluminophosphate lattice. So the incorporation of a transition metal or

lanthanide cation can easily change its oxidation number and also creates redox

active site. The coupling of acidic with redox properties opens up routes

towards shape selective bi-functional catalysts and design of novel catalysts.

The location and local structure (metal ion environment) of the incorporated

metal ions are necessary for optimization and control of the catalytic activity in

these systems. The catalytic properties of microporous materials are largely

determined by the composition and structure on the atomic scale. Therefore,

catalyst characterization is a highly relevant discipline in catalysis.

Different characterization techniques are used to gain an insight into

the location of the transition metal ions in aluminophosphate framework.

Generally, data on the location of the cations are collected with difficulty since

the metal concentration is usually low. It is necessary to use more than one

method if a reliable conclusion is to be reached. Characterization techniques

such as diffuse reflectance UV-Vis spectroscopy (DRS), electron spin

resonance (ESR), electron spin echo modulation (ESEM), Fourier transform

72

infrared (FT-IR) and diffuse reflectance infrared Fourier transform (DRIFT)

spectroscopies are commonly applied. Nuclear magnetic resonance

spectroscopy (NMR), Mössbauer spectroscopy, X-ray absorption near-edge

structure (XANES) and extended X-ray absorption spectroscopy for fine

structure (EXAFS) are also employed occasionally. Therefore, suitable

complementary characterization techniques are necessary to understand the

surface chemistry of microporous AlPO4 materials.

In the present study XRD, DRS-UV-Vis, BET, SEM, TEM, ESR,

XPS, 27Al and 31P MAS-NMR, FT-IR, TGA, TPD, TPR, ex-situ pyridine

adsorbed IR and ICP-OES were employed to correlate the physico-chemical

properties of the synthesized catalysts and their catalytic activities.

3.2 PHYSICOCHEMICAL CHARACTERIZATION OF PrAlPO-5

3.2.1 X-Ray Diffraction (XRD)

The XRD patterns of calcined AlPO-5, PrAlPO-5 (25, 50, 75, 100,

150 and 200) and Pr6O11 are shown in Figure 3.1. Pure Pr6O11 showed

reflections close to 28, 33, 47 and 56° (2 ) corresponding to (111), (200), (220)

and (311) reflections respectively (Ma ecka & Kepinski 2007, Abu–Zied &

Soliman 2008). All PrAlPO-5 catalysts exhibited characteristic reflections of

AlPO-5 (Fang et al 1997) and not that of Pr6O11, thus confirmed the absence of

extra framework praseodymium species in any of the PrAlPO-5.

Praseodymium incorporated AlPO-5 molecular sieves showed a change in the

order of intensity of reflections from that of parent AlPO-5. Since the intensity

of different reflections of PrAlPO-5 (25 and 50) exhibited the same order as

that of AlPO-5, it is presumed that all of them possessed the same crystal

morphology. Although the reflections of PrAlPO-5 (75, 100, 150 and 200)

exhibited similar to that of AlPO-5 and PrAlPO-5 (25 and 50), the intensity of

reflections changed. For example, the reflection at 2 = 18° became intense

peak, and based on the increase in intensity it could be inferred that

73

praseodymium was better located in (210) plane compared to other planes.

When praseodymium content was low as in the case of PrAlPO-5 (75, 100, 150

and 200), it chose specific plane and the intensity of reflections changed from

the parent AlPO-5. The lattice parameters and d spacing values for AlPO-5 and

PrAlPO-5 samples were calculated, and the results are presented in Table 3.1.

Praseodymium incorporated AlPO-5 showed higher lattice parameter values

than that of parent AlPO-5, and the inter-planar distance (d100) increased

linearly with increase of praseodymium content.

Figure 3.1 XRD patterns of calcined (a) AlPO-5, (b) PrAlPO-5 (25), (c) PrAlPO-5 (50), (d) PrAlPO-5 (75), (e) PrAlPO-5 (100), (f) PrAlPO-5 (150), (g) PrAlPO-5 (200) and (h) Pr6O11

74

The angular positions of reflections (2 ) of PrAlPO-5 samples showed a slight

shift from the parent AlPO-5. The shift in 2 values and change in the lattice

parameter values of PrAlPO-5 compared to AlPO-5 supported framework

incorporation of praseodymium.

Table 3.1 Lattice parameter values for AlPO-5 and PrAlPO-5

Catalyst

(calcined) a=b C

d(100)

(Å)

AlPO-5 13.4233±0.1645 8.4061±0.2453 11.40

PrAlPO-5(200) 13.7075±0.0153 8.6029±0.1889 11.95

PrAlPO-5(150) 13.7361±0.009 8.4824±0.0483 11.98

PrAlPO-5(100) 13.7886±0.0221 8.5110±0.0420 12.00

PrAlPO-5(75) 13.8549±0.0315 8.3912±0.0587 12.07

PrAlPO-5 (50) 13.8676±0.0135 8.4591±0.0147 12.12

PrAlPO-5 (25) 13.8709±0.0213 8.4672±0.0321 12.13

3.2.2 Diffuse Reflectance Ultraviolet-Visible(DRS-UV-Vis)

Spectroscopy

The DRS-UV-Vis spectra of AlPO-5 supported 3 wt% Pr6O11, AlPO-

5 are shown in Figure 3.2, and praseodymium incorporated AlPO-5 (25, 50, 75,

100, 150 and 200) catalysts are shown in Figure 3.3. AlPO-5 did not show any

absorbance in the UV-Vis region. The trivalent praseodymium (Pr3+) contained

two electrons in its 4f orbital which gave rise to a number of distinct

microstates whose term symbols are 3H4, 3H5, 3H6, 3F2, 3F3, 3F4, 1G4, 1D2, 3P0,3P1, 3P2, 1I6 and 1S0. Hence, a series of f-f transition were possible (Carnall et al

1989). The 3 wt% Pr6O11 loaded AlPO-5 showed a broad band between 415

and 590 nm with a fine structure which is attributed to f-f transition of Pr3+ ions

(Ma ecka & Kepinski 2007, Barrera et al 2007).

75

Figure 3.2 DRS UV-Vis spectra of (a) AlPO-5 and (b) AlPO-5 supported 3 wt%Pr6O11

Figure 3.3 DRS UV-Vis spectra of (a) PrAlPO-5 (200), (b) PrAlPO-5 (150), (c) PrAlPO-5 (100), (d) PrAlPO-5 (75), (e) PrAlPO-5 (50) and (f) PrAlPO-5 (25)

76

PrAlPO-5 molecular sieves showed three bands around 210, 262 and

380 nm. Donega et al (1995) reported the band around 210 nm is assigned to

O2- to Pr3+ charge transfer transition. The band at 262 nm is quite broad and it is

due to the appearance of induced electron dipole f-f transition (Dorenbos 2000)

(Jude-Ofelt theory) and O2- to Pr4+ charge transfer transition (Tankov et al

2011) in that region. The promotion of 4f electron into 5d sub-shell is Laporte

allowed and they are broad (around 250 nm) which overlap with O2- to Pr4+

charge transfer transition at 270 nm, and observed as a broad peak centered

around 262 nm. Further, the band at 210 and 270 nm are the characteristics of

Pr (III and IV) species in the tetrahedral position. These observations supported

the framework incorporation of Pr in AlPO-5 framework.

3.2.3 Surface Microstructure (SEM and HR TEM)

The SEM images of calcined AlPO-5 and PrAlPO-5 are shown in

Figure 3.4. The image exhibited hexagonal rods of smooth surface. Zhao et al

(2006) and Fang et al (1997) also reported similar morphology. The SEM

image of PrAlPO-5 (100) shown in Figure 3.4d, illustrates similar features as

shown in Figure 3.4a. There were hexagonal aggregated rods and most of the

rods were cleaved along the longitudinal direction. The SEM image of PrAlPO-

5 (75) (Figure 3.4e) was nearly the same as that of Figures 3.4a and 3.4g. Both

PrAlPO-5 (25) and PrAlPO-5 (50) also exhibited similar morphology (Figures

3.4g and 3.4f).

77

Figure 3.4 SEM images of (a) AlPO-5, (b) PrAlPO-5 (200), (c) PrAlPO-5 (150), (d) PrAlPO-5 (100), (e & h) PrAlPO-5 (75), (f) PrAlPO-5 (50) and (g) PrAlPO-5 (25)

Although the XRD pattern of PrAlPO-5 ((Al+P)/Pr = 75 and 100)

exhibited change in the order of reflections from that of parent AlPO-5, the

morphology of the material did not change. This revealed that the concentration

of praseodymium in the synthesis gel didn’t affect the nucleation process. The

appearance of tiny crystallites on the surface of hexagonal rods was due to slow

condensation of hydroxides of praseodymium with phosphates. The

aggregation of small particles created large number of voids, which are clearly

evidenced in the TEM images (Figure 3.5)

78

Figure 3.5 TEM images of (a) AlPO-5, (b) PrAlPO-5 (200), (c) PrAlPO-5 (150), (d) PrAlPO-5 (100), (e) PrAlPO-5 (75), (f) PrAlPO-5 (50) and (g) PrAlPO-5 (25)


The nitrogen sorption isotherms of calcined AlPO-5 and PrAlPO-5 with (Al+P)/Pr ratios of 25, 50, 75, 100, 150 and 200 molecular sieves are shown in Figure 3.6. The hysteresis loop observed just below the relative pressure (p/p0) of one is due to inter particle voids. The TEM images (Figure 3.5) also revealed such large number of voids due to aggregation of particles. The small angle XRD (Figure 3.7) pattern also supported the absence of mesopores as it did not exhibit any characteristic reflection at low 2 as that of ordered mesoporous materials. The BET surface area and pore volume of the materials are presented in Table 3.2. Li et al (2010) reported increase in surface area and pore volume due to incorporation of lanthanides in AlPO-5 framework. The increase in surface area and pore volume with Pr incorporation in AlPO-5 concurred with Li et al (2010) report. The larger ionic radii of Pr (III and IV) than that of Al (III) and P (V) ions altered the lattice parameters of AlPO-5 crystals. Such increase in lattice parameters increased the crystal size which in turn increased the surface area and pore volume of the materials. Thisincrease in surface area and pore volume also supported framework incorporation of praseodymium in AlPO-5.

79

Figure 3.6 N2 sorption isotherms of (a) AlPO-5, (b) PrAlPO-5 (200), (c) PrAlPO-5 (150), (d) PrAlPO-5 (100), (e) PrAlPO-5 (75), (f) PrAlPO-5 (50) and (g) PrAlPO-5 (25)

Figure 3.7 Small angle XRD pattern of PrAlPO-5 (75)

80

Table 3.2 Nitrogen sorption results of calcined AlPO-5 and PrAlPO-5 (25, 50, 75, 100, 150 and 200)

CatalystSurface

area, ABET

(m2/g)a

Pore volume Vp

(cm3/g)b

Pore diameter,

Dp

(Å)c

AlPO-5 228 0.20 4.36PrAlPO-5 (25) 272 0.28 5.18PrAlPO-5 (50) 265 0.27 5.03PrAlPO-5 (75) 258 0.25 4.89PrAlPO-5 (100) 245 0.24 4.69PrAlPO-5 (150) 242 0.23 4.56PrAlPO-5 (200) 239 0.22 4.50acalculated from N2 adsorption-desorption isotherm, b & cDetermined by BJH method

3.2.5 Electron Spin Resonance Spectroscopy (ESR)

The ESR spectra of PrAlPO-5 (25, 50, 75, 100, 150 and 200)

recorded at room temperature are shown in Figure 3.8. All the six spectra

showed signals around g values of 1.9 and 3.4 due to paramagnetic

praseodymium species. PrAlPO-5 (200, 150 and 100) showed sharp ESR

signals due to oxygen chemisorbed on Pr3+ sites whereas PrAlPO-5 (25, 50 and

75) showed broad and resolved signals for free Pr3+ and Pr4+ sites. Since the

metal content in PrAlPO-5 (75) was relatively higher than all other PrAlPO-5,

incorporation of high amount of praseodymium in the framework led to

collapse of structure. In order to avoid such a ring strain, part of Pr3+ species

was oxidized to Pr4+ by chemisorbed oxygen. Hence well resolved signals for

Pr3+ and Pr4+ appeared in the ESR spectrum of PrAlPO-5 (25, 50 and 75). The

ESR signal close to g value of 2.0 is attributed to oxygen

chemisorbed on praseodymium species. Maurelli et al (2012) and

82

Cheralathan et al (2000) already reported similar observations for metal

incorporated aluminophosphates. Lu et al (2005) reported that the signal with

similar g value of 2.0 was assigned to framework defects in AlPO-5. Trojan et

al (1992) reported the magnetic behavior of phthalocyanine ligands that

exhibited a strong magnetic interaction with lanthanide f-electrons and trivalent

Pr in bis(phthalocyaninato) complexes which showed a spin resonance signal at

g = 2.0. The low temperature ESR spectra of PrAlPO-5 (75) recorded at 200

and 110 K and that of PrAlPO-5 (25) recorded at 110 K (Figure 3.9) showed

two distinct peaks at g values of 2.0 and 2.045. The former g value suggested

magnetic interaction of Pr species with paramagnetic oxygen molecule and the

later suggested the presence of defective AlPO-5 sites. Hence the magnetic

interaction of oxygen with Pr species was confirmed and also supported the

framework incorporation of Pr in AlPO-5.

83

Figure 3.9 Low temperature ESR spectra of (a) PrAlPO-5 (25) and (b & c) PrAlPO-5 (75)


The XPS spectrum (Figure 3.10) of Pr 3d core electron levels for

calcined PrAlPO-5(75) revealed the oxidation state of praseodymium in

AlPO-5. The two broad peaks around 938 and 959 eV are assigned to Pr 3d5/2

and Pr 3d3/2 states respectively (Barrera et al 2007). De-convolution of the peak

(3d5/2) established the presence of Pr3+ and Pr4+ species. The peak around

933 eV is assigned to Pr3+, and the peak around 935 eV is assigned to Pr4+

oxidation state. Similar de-convolution of Pr 3d3/2 peak results two peaks

around 953 and 955 eV. The comparison of intensity of the peaks revealed that

Pr3+ content is slightly lower than that of Pr4+.

84

Figure 3.10 XPS spectrum of calcined PrAlPO-5 (75)

3.2.7 27Al and 31P Magic Angle Spinning – NMR

27Al MAS-NMR of AlPO-5 and PrAlPO-5 (25 and 75) are shown in

Figure 3.11. The 27Al MAS-NMR of AlPO-5 exhibited a broad peak between

30 and 50 ppm (Akholekar & Ryoo 1996). It showed seven overlapped peaks

due to quadrupolar interactions. The 27Al MAS-NMR of PrAlPO-5 (25)

showed an intense peak at 37.93 ppm due to tetrahedral aluminium, and a weak

peak at 4.96 ppm due to aluminium in distorted trigonal bipyramidal co-

ordination. Similarly PrAlPO-5 also showed an intense peak at 37.63 ppm, and

a weak peak around 6.04 ppm. Both PrAlPO-5 (25) and PrAlPO-5 (75) showed

a peak around -15 ppm. The paramagnetic praseodymium species present in the

framework delocalized the unpaired electron through oxygen linkage which led

to the appearance of negative signals in the spectra (Zhao et al 2006)

85

Figure 3.11 27Al MAS-NMR spectra of AlPO-5 and PrAlPO-5 (25 and 75)

27Al MAS-NMR of AlPO-5

27Al MAS-NMR of PrAlPO-5 (25)

27Al MAS-NMR of PrAlPO-5 (75)

86

The 31P MAS-NMR of AlPO-5 and PrAlPO-5 (25 and 75) are shown in

Figure 3.12. AlPO-5 showed an intense sharp peak at -24.62 ppm (Li & Davis

1993). This confirmed only one type of crystallographic phosphorous in

AlPO-5. This peak is shifted to -27.86 ppm in PrAlPO-5 (25). The shoulder to

the main peak observed for PrAlPO-5 (25) suggested different environment for

framework phosphorous. The 31P MAS-NMR of PrAlPO-5 (75) also exhibited

a strong peak at -27.52 ppm along with a shoulder peak at -31.21 ppm. The

appearance of two resonance signals confirmed the framework substitution of

Pr for Al. Further, 31P MAS-NMR showed spinning side bands due to dipolar

interaction with paramagnetic praseodymium species. The MAS-NMR study

thus confirmed the framework incorporation of praseodymium by replacing

both Al and P ions in the framework of AlPO-5.

87

31P MAS-NMR of PrAlPO-5 (75)

* *

Figure 3.12 31P MAS-NMR spectra of AlPO-5 and PrAlPO-5 (25 and 75)

31P MAS-NMR of AlPO-5



88

3.2.8 Temperature Programmed Reduction (TPR)

The TPR profiles of AlPO-5 supported 3 wt% Pr6O11 and PrAlPO-5

with (Al+P)/Pr ratios 25, 50, 75 and 100 molecular sieves were recorded

between 100 and 900 oC and are shown in Figure 3.13. The AlPO-5 supported

3 wt% Pr6O11 showed two reduction peaks around 610 and 720 oC. Such

reduction peaks were not observed in all PrAlPO-5 molecular sieves. This

further confirmed the absence of non-framework praseodymium species in

AlPO-5.

Figure 3.13 TPR profile of (a) AlPO-5 supported 3 wt% Pr6O11,

(b) PrAlPO-5 (100), (c) PrAlPO-5 (75), (d) PrAlPO-5 (50) and

(e) PrAlPO-5 (25)

89

3.2.9 Characterization of Acid Sites (TPD-NH3 and ex-situ pyridine

adsorbed IR)

The surface acidity in PrAlPO-5 was investigated by temperature

programmed desorption of ammonia (TPD-NH3) and ex-situ pyridine adsorbed

IR. The TPD-NH3 results of AlPO-5, AlPO-5 supported 3 wt% Pr6O11 and

PrAlPO-5 with (Al+P)/Pr ratios 25, 50, 75, 100, 150 and 200 are depicted in

Figure 3.14 and Figure 3.15 respectively. The presence of weak and moderately

strong acid sites was evidenced by the appearance of two distinct peaks around

150 and 350 °C (Pastore et al 2005). The MAS-NMR study also confirmed that

Pr replaced both Al and P in the framework. The isomorphic substitution of

phosphorous by praseodymium created mild Bronsted acid sites.

Figure 3.14 TPD-NH3 profile of (a) AlPO-5 and (b) AlPO-5 supported 3

wt% Pr6O11

90

Figure 3.15 TPD-NH3 profile of (a) PrAlPO-5 (200), (b) PrAlPO-5 (150),

(c) PrAlPO-5 (100), (d) PrAlPO-5 (75), (e) PrAlPO-5 (50) and

(f) PrAlPO-5 (25)

The desorption peak between 300 and 410 °C attributed to moderately strong

acid sites also supported this view. The total acidity of the material increased

with increase in praseodymium content (Table. 3.3). The acidity created in

PrAlPO-5 molecular sieve was mainly due to incorporation of praseodymium

in the framework. Dumitriu et al (2002) illustrated the TPD profile for metal

incorporated AFI catalysts with intermediate acid strength. The results

concurred with Dumitriu et al (2002) report. The pyridine adsorbed IR spectra

of PrAlPO-5 (75, 100 and 150) are shown in Figure 3.16. The adsorption of

pyridine led to the formation of coordinated bands around 1445, 1490 and 1598

cm-1 (Huang et al 2003, Liu et al 2008). These are the characteristic bands of

Lewis acid sites present in a solid acid catalyst. The very weak band around

1547 cm-1 suggested the presence of a few number of Bronsted acid sites in the

PrAlPO-5 catalysts.

91

Table 3.3 TPD-NH3 sorption results of calcined samples

Catalyst Total aciditiya

(mmol NH3/g)

AlPO-5 -

PrAlPO-5 (25) 0.174

PrAlPO-5 (50) 0.170

PrAlPO-5 (75) 0.165

PrAlPO-5 (100) 0.158

PrAlPO-5 (150) 0.137

PrAlPO-5 (200) 0.106aNH3-TPD

Figure 3.16 Ex-situ pyridine adsorbed IR spectra of (a) PrAlPO-5 (150),

(b) PrAlPO-5 (100), (c) PrAlPO-5 (75) and (d) PrAlPO-5 (25)

92

3.2.10 FT-IR Spectroscopy

The FT-IR spectra of calcined PrAlPO-5 ((Al+P)/Pr = 25, 50, 75,

100, 150 and 200) and AlPO-5 samples were recorded between 4000 and

400 cm-1 (Figure 3.17). The asymmetric stretching vibration of TO4 groups (Al-

O-P and Al-O-Pr) appeared between 1300 and 850 cm-1, and the corresponding

bending vibration appeared around 750 cm-1 (Zecchina & Arean 1996). The

bending vibration of PrAlPO-5 samples showed decrease in intensity and

broadened with fine structure (peak around 512 and 580 cm-1) thus indicated

Pr-O linkage, which was absent in AlPO-5. This also supported the

incorporation of praseodymium species in AlPO-5 framework. The band

appeared below 500 cm-1 is due to vibrations in double ring region. The band

just below 3000 cm-1 due to C-H stretching vibration was absent in all the

calcined samples. This confirmed the complete removal of template during

calcination.

93

Figure 3.17 FT-IR spectra of (a) AlPO-5, (b) PrAlPO-5 (200), (c) PrAlPO-

5 (150), (d) PrAlPO-5 (100), (e) PrAlPO-5 (75), (f) PrAlPO-5

(50) and (g) PrAlPO-5 (25)

3.2.11 Thermogravimetric Analysis (TGA)

The thermograms of assynthesized AlPO-5 and PrAlPO-5 with

(Al+P)/Pr ratios of 25, 50, 75 and 100 are shown in Figure 3.18. All the

samples showed a weight loss between 70 and 100 oC due to removal of

physisorbed water. The second weight loss between 200 and 560 oC was due to

removal and decomposition of the template. The removal of template occurred

in two stages in the case of PrAlPO-5 molecular sieves. First the template

adsorbed at weak acid sites lost below 400 oC, and then the decomposition of

94

template occurred between 400 and 560 oC due to the presence of strong acid

sites. Similar behavior was already reported by Umamaheswari et al (2000).

Figure 3.18 TGA of as-synthesized (a) AlPO-5, (b) PrAlPO-5 (100),

(c) PrAlPO-5 (75), (d) PrAlPO-5 (50) and (e) PrAlPO-5 (25)

The thermograms of calcined AlPO-5 and PrAlPO-5 molecular

sieves are shown in Figure 3.19. The weight loss below 100 oC increased with

increase of metal content thus suggested the hydrophilic nature of the catalysts.

This confirmed not only the complete removal of template but also the

hydrophilic nature of metal incorporated AlPO-5 molecular sieves.

95

Figure 3.19 TGA of calcined (a) AlPO-5, (b) PrAlPO-5 (100),

(c) PrAlPO-5 (75), (d) PrAlPO-5 (50) and (e) PrAlPO-5 (25)

3.3 PHYSICO-CHEMICAL CHARACTERIZATION OF FeAlPO-5

3.3.1 X-ray Diffraction (XRD)

The XRD patterns of calcined FeAlPO-5 (75, 100 and 150) and

Fe2O3 are shown in Figure 3.20. The XRD patterns showed intense peaks at 2

values of 7.56, 13.04, 15.08, 20, 21.06 and 22.62° corresponding to the

diffractions of (100), (110), (200), (210), (002) and (211) planes respectively

[JCPDS: 41-0044]. These are the characteristic reflections of AlPO-5

molecular sieves (Shiju et al 2006). Further, the XRD patterns of FeAlPO-5

molecular sieves did not show any reflections corresponding to Fe2O3 (Soria

et al 2014) thus confirmed the absence of separate Fe2O3 phase. The lattice

parameters increased with increase of iron content, and the inter-planar

96

distance also linearly increased with increase of iron content. The angular

positions of reflections were shifted to lower 2 values with the increase of iron

content. The lattice parameters for AlPO-5 and FeAlPO-5 were calculated and

presented in Table 3.4.The change in lattice parameters, d-spacing values and

shift in 2 values are supportive for the framework incorporation of iron in

AlPO-5.

Figure 3.20 XRD patterns of (a) FeAlPO-5 (150), (b) FeAlPO-5 (100), (c) FeAlPO-5 (75) and (d) Fe2O3

97

Table 3.4 Lattice parameters for calcined AlPO-5 and FeAlPO-5

Catalyst a=b cd(100)

(Å)

V

(Å)3

AlPO-5 13.5495±0.1451 8.3805±0.2239 11.51 1332.43

FeAlPO-5(150) 13.6523±0.891 8.4513±0.0660 11.61 1364.17

FeAlPO-5(100) 13.6858±0.0100 8.4961±0.0158 11.75 1378.14

FeAlPO-5(75) 13.6975±0.0085 8.4857±0.0184 11.82 1378.80

3.3.2 Diffuse Reflectance Ultraviolet-Visible (DRS-UV-Vis)

Spectroscopy

DRS-UV-Vis spectra of calcined FeAlPO-5 (75, 100 and 150)

molecular sieves are presented in Figure 3.21. The calcined FeAlPO-5 samples

showed a single intense broad band around 253 nm in the UV region. This

band is attributed to the Laporte allowed ligand to metal (O2- to Fe3+) charge

transfer transition (Selvam & Mohapatra 2006, Wang et al 2004). The peak

around 253 nm also confirmed the tetrahedral geometry of Fe3+ in [FeO4]-.

Further, the absence of peak between 400 and 700 nm confirmed the absence of

clustering of iron species and extra-framework iron species (Wei et al 2008).

98

Figure 3.21 DRS UV-Vis spectra of (a) FeAlPO-5 (150), (b) FeAlPO-5 (100) and (c) FeAlPO-5 (75)

99

3.3.3 Scanning Electron Microscopic (SEM) Analysis

The SEM images of calcined AlPO-5 and FeAlPO-5 are shown in

Figure 3.22. The AlPO-5 and FeAlPO-5 (75, 100 and 150) showed hexagonal

morphology. Guo et al (2005) already reported hexagonal morphology for

AlPO-5 crystals. This suggested that the incorporation of iron in AlPO-5

framework did not affect the morphology of AlPO-5 crystals. The XRD

patterns also revealed that the crystals belonged to hexagonal space group of

P6cc.

Figure 3.22 SEM images of (a) AlPO-5, (b) FeAlPO-5 (75), (c) FeAlPO-5

(100) and (d) FeAlPO-5 (150)

100


The nitrogen sorption isotherms of calcined AlPO-5, fresh and used

FeAlPO-5 (75) are shown in Figure 3.23. The N2 sorption isotherm of

FeAlPO-5 at high relative pressure showed a hysteresis loop of H1 type, which

concurred with typical microporous material (Sing et al 1985).

Figure 3.23 Nitrogen sorption isotherms of (a) AlPO-5, (b) fresh FeAlPO-

5 (75) and (c) used FeAlPO-5 (75)

101

The BET surface area, pore volume and average pore diameter of the

materials are presented in Table 3.5. The textural parameters especially average

pore size of both fresh and used FeAlPO-5 catalysts remained almost the same

and in good agreement with the parent AlPO-5 suggesting that the zeotype kept

its original structure. Further, the incorporation of iron in the framework

slightly increased the BET surface area of FeAlPO-5. These observations also

supported the framework incorporation of Fe in AlPO-5

Table 3.5. Nitrogen sorption results for fresh and used FeAlPO-5 catalyst

Catalyst BET Surface area

(m2/g)

Micropore

volumea (cm3/g)

Mesopore

volumeb (cm3/g)

AlPO-5 225 0.101 0.284

FeAlPO-5(75) (fresh) 245 0.108 0.287

FeAlPO-5(75) (used) 241 0.107 0.288a Calculated by t-plot method, b Calculated by BJH method

3.3.5 Electron Spin Resonance Spectroscopy (ESR)

The ESR spectra of calcined FeAlPO-5 (75, 100 and 150) recorded

at room temperature are shown in Figure 3.24. All the three spectra showed

signals around g values of 4.3 and 2.0. Goldfarb et al (1994) reported that the g

value of 2.0 was due to Fe3+ in tetrahedral site while the g value of 4.3

attributed to distorted tetrahedral. However, the signal around g value of 2.0

could also be assigned to Fe3+ in oxidic clusters (Catana et al 1995). In order to

study the chemical location of Fe3+ ion, the ESR spectra were compared with

DRS-UV-Vis spectra. The absence of peak between 400 and 700 nm in DRS-

UV-Vis spectra excluded the possibility of extra framework Fe3+ and clustering

of iron species. Hence it is concluded that iron incorporated in AlPO-5

framework is in tetrahedral sites.

102

Figure 3.24 ESR spectra of (a) FeAlPO-5 (75), (b) FeAlPO-5 (100) and (c)

FeAlPO-5 (150)


The XPS spectrum was recorded in order to establish the oxidation

state of iron in AlPO-5. The core level XPS spectrum of iron in FeAlPO-5 (75)

is depicted in Figure 3.25. The peaks due to Fe 2p3/2 occurred at 710.1 eV and

that of Fe 2p1/2 at 723.9 eV. Similar values were reported in literature for Fe3+

ions by Yamashita and Hayes (2008) and Bhargaba et al (2007). Hence the

oxidation state of iron in FeAlPO-5 was established to be +3. The ESR and

DRS-UV-Vis studies supported the presence of iron in trivalent oxidation state.

103

Figure 3.25 XPS spectrum of calcined FeAlPO-5 (75)

3.3.7 Characterization of Acid Sites (TPD-NH3 and ex-situ pyridine

adsorbed IR)

The surface acidity in FeAlPO-5 was determined by temperature

programmed desorption of ammonia (TPD-NH3) and ex-situ pyridine adsorbed

IR. The TPD-NH3 results of FeAlPO-5 (75, 100 and 150) are depicted in Figure

3.26. A strong peak around 120 °C was observed, and this peak position shifted

towards higher temperature with slight increase of Fe content. This suggested

that the strength of acid sites increased with increase of metal content. The total

acidity of the material was calculated from the area under the peak and

presented in Table. 3.6. This confirmed the incorporation of iron in AlPO-5

created acidic nature to FeAlPO-5 catalysts (Dumitriu et al 2002, Pastore et al

104

2005). The ex-situ pyridine adsorbed IR spectra of FeAlPO-5 (75, 100 and 150)

are shown in Figure 3.27. The peaks observed at 1445, 1490 and 1598 cm-1 are

assigned to pyridine coordinated to Lewis acid sites (Huang et al 2003,

Liu et al 2008). The weak peak around 1545 cm-1 is due to interaction of

pyridine with Bronsted acid sites. This peak is very weak in comparison with

peak at 1445 cm-1, thus established that FeAlPO-5 contained more number of

Lewis acid sites than Bronsted acid sites.

Figure 3.26 TPD-NH3 profile of (a) FeAlPO-5 (150), (b) FeAlPO-5 (100) and (c) FeAlPO-5 (75)

105

Table 3.6 TPD-NH3 sorption results of calcined FeAlPO-5 catalysts

Catalyst Total aciditya

(mmol NH3/g)

AlPO-5 -

FeAlPO-5 (150) 0.107

FeAlPO-5 (100) 0.128

FeAlPO-5 (75) 0.145aNH3-TPD

Figure 3.27 Ex-situ pyridine adsorbed IR spectra of calcined FeAlPO-5 (75)

106

CHAPTER 4

LIQUID PHASE AEROBIC OXIDATION OF

ETHYLBENZENE OVER PrAlPO-5

4.1 INTRODUCTION

Selective catalytic oxidation of alkyl aromatics is a viable

technology to functionalize saturated and unsaturated hydrocarbons (Wentzel

et al 2000).The benzylic oxidation of alkyl aromatics is considered to be one

of the important catalytic reactions for the preparation of corresponding

carbonyl compound of the reactant as they are used in the synthesis of fine

chemicals and pharmaceuticals (Lu et al 2010). Parida& Dash (2009) studied

the liquid phase oxidation of ethylbenzene using TBHP as oxidant under mild

reaction conditions at a temperature of 80 °C. They reported 57.7%

ethylbenzene conversion and selectivity to acetophenone (82.2%) and

benzaldehyde (18%).The catalytic oxidation of ethylbenzene over Co-

substituted heteropolytungstate catalyst using H2O2 oxidant with acetonitrile

as solventgave acetophenone (93%) and 1-phenylethanol

(Kanjina&Trakarnpruk 2010).Kanjina&Trakarnpruk (2011) reported the

selective oxidation of ethylbenzene to acetophenone using tert-

butylhydroperoxide (TBHP) as oxidant at 130 °C in the presence of mixed

metal oxide catalysts. The reaction showed 87% ethylbenzene conversion and

92% selectivity to acetophenone.

Vanadia supported on ceria catalysts were used in the liquid phase

oxidation of ethylbenzene using H2O2 oxidant (Radhika et al 2007).

107

Acetophenone was found to be the major product along with

2-hydroxyacetophenone as minor product.The sintering at high temperature

and leaching of metal ions are serious drawbacks of transition metal oxide

based catalysts (Yu et al 2006). Organic peroxides, hydrogen peroxide and

molecular oxygen are cost effective oxidants for the oxidation of alkyl

aromatics in the presence of a suitable catalytic system. However, organic

peroxides are not environmentally benign as they leave large volume of

organic waste. Hydrogen peroxide decomposedrapidly above 70 °C, as a

consequence the formation of water in the reaction mixture decreased the

activity of the catalyst by decreasing the interaction between the substrate and

the catalyst surface. Molecular oxygen (air) is the cheapest and clean

oxidizing agent. Perkas et al (2001) reported the aerobic oxidation of

cyclohexane over mesoporous iron-titania catalyst. The reaction showed 90%

selectivity to cyclohexanol. Rajuet al (2008) reported supported Ni catalysts

for the aerobic oxidation of ethylbenzene. They concluded that Ni based

systems were active for the sidechain oxidation of ethylbenzene and the

formation of products was anchored by acidity of the catalysts.

Selective oxidation of ethylbenzene catalyzed by fluorinated

metalloporphyrins with molecular oxygen (Li et al 2007) gave 94%

acetophenone with a turnover number of 2719 under mild conditions. Solvent

plays an important role in the liquid phase reactions (Mal &Ramasamy 1996,

Jha et al 2006). However, the use of solvent also led to environmental

problems. Guo et al (2003) reported solvent free aerobic oxidation of

cyclohexene. Tusar et al (2011) reported solvent free oxidation of alkyl

aromatics to aromatic ketones using molecular oxygen. Zhan et al (2007),

Tian et al (2004), Araujo et al (2003) and Devika et al (2012) reported a

variety of metal incorporated AlPO-5 molecular sieves for the selective

oxidation of organic molecules. Devika et al (2011) interpreted the

paramagnetic behavior of Ce3+ ions in CeAlPO-5 molecular sieves and

108

oxygen chemisorption behavior in the selective oxidation of ethylbenzene. In

the lanthanide family, praseodymium the successor of cerium has two lone

pair electrons in the 4f shell which couldexhibit better interaction with

molecular oxygen than cerium. Since Pr3+ and Pr4+ are paramagnetic in nature,

they can activate molecular oxygen and thus facilitate the oxidationof

ethylbenzene.

The framework substitution of praseodymium in the molecular

sieves can combine the high activity and selectivity of homogeneous catalysts

with ease of recovery and recycling, which are characteristics of

heterogeneous catalysts. The high surface area is an additional advantage

acquired by framework incorporation of praseodymium into AlPO-5.

Further,the weak and moderate acid sitescreated in PrAlPO-5 framework

aided side chain oxidation rather than ring hydroxylation (Reddy et al 1993,

Mal et al 1995, Chen et al 1996, Selvam&Singh 1995, Chen &Sheldon 1995).

Keeping in mind the advantages of framework incorporation of

praseodymium into AlPO molecular sieves, in the present study PrAlPO-5

with different (Al+P)/Pr ratios in fluoride medium were synthesized and

evaluated their catalytic activity in the liquid phase aerobic oxidation of

ethylbenzene.


Solvent free liquid phase aerobic oxidation of ethylbenzene was

carried over PrAlPO-5 molecular sieves in the temperature range 60-140 oC.Acetophenone was found to be the major product (>90%) and 1-

phenylethanol, 2-phenylethanol, phenyl acetaldehyde and phenyl acetic acid

as minor products (Scheme 4.1).

109

Scheme 4.1Aerobic oxidation of ethylbenzene

The influence of reaction parameters such as temperature, reaction

time, substituents and Pr content was also studied. The plausible mechanism

for the reaction is depicted in Scheme 4.2. In this mechanism, Pr3+ is oxidized

to Pr4+ by the chemisorbed oxygen. This then abstracts a hydrogen from the

methylene group of ethylbenzene, thus forming metal hydroperoxide and

phenyl ethyl radical. The formation of 1-phenylethanol is attributed to the

reaction between metal hydroperoxide and phenyl ethyl radical. Further, the

oxygen radical present in Pr4+ abstracts a hydrogen from 1-phenylethanol to

form a tertiary radical which eliminates a molecule of water thus resulting

acetophenone. The reaction was carried out between 60 and 140 oC. There

was practically no reaction in this temperature range in the absence of

catalyst. Further, the reaction did not proceed in nitrogen atmosphere instead

of air atmosphere. This supported the proposed reaction mechanism.

110

Scheme 4.2 Possible pathway for the oxidation of ethylbenzene to acetophenone

4.2.1 Effect of Temperature

Liquid phase oxidation of ethylbenzene in the presence of air was

carried over PrAlPO-5 (25, 50, 75 and 100) catalysts in the temperature range

60-140 oC. The experimental results are presented in Table 4.1. The ethyl

benzene conversion and acetophenone selectivity were found to be maximum

at 120 oC. When the reaction temperature was increased above 120 oC, there

was no significant improvement in the selectivity of 1-phenylethanol whereas

selectivity to others increased appreciably. The acetophenone selectivity also

decreased considerably above this reaction temperature. 2-Phenylethanol,

phenyl acetaldehyde and phenyl acetic acid were formed at 140 oC due to

activation of methyl group. Since the formation of acetophenone from

1-phenylethanol is a rapid reaction, the formation of 1-phenyl ethane-1,2-diol

is ruled out. The competition of additional reaction forming phenyl acetic acid

112

suppressed 1-phenylethanol formation, and this decreased the selectivity to

acetophenone. Thus, ethylbenzene conversion remained the same but the

selectivity to acetophenone decreased over PrAlPO-5 catalysts above 120 oC.

4.2.2 Effect of (Al+P)/Pr Ratios

PrAlPO-5 with different (Al+P)/Pr ratios viz., 25, 50, 75 and 100

were used for the aerobic oxidation of ethylbenzene and the results are

presented in Table 4.1. PrAlPO-5 with (Al+P)/Pr ratio 25 showed slightly

higher selectivity to acetophenonethan others at 120 °C. Since Pr content in

this catalyst was high, it could rapidly converted 1-phenylethanol to

acetophenone. The decrease of 1-phenylethanol selectivity also supported this

view. As 1-phenylethanol is a neutral compound, and there is also an

appreciable steric hindrance for adsorption on Pr sites through its –OH group,

it can rapidly diffuse out. Hence,increase of framework Pr content in AlPO-5

could rapidly converted 1-phenylethanol to acetophenone. This study revealed

the dependence of acetophenone selectivity on the framework Pr content in

AlPO-5.

4.2.3 Effect of Reaction Time

The influence of reaction time on conversion and selectivity was

studied between 1 and 10 h over PrAlPO-5 (25) at 120 oC and the results are

depicted in Figure 4.1. The percentage conversion of ethyl benzene increased

from 1 to 6 h reaction time. Though ethylbenzene conversion remained the

same upto 10 h, the selectivity to acetophenone decreased. The concentration

of acetophenone was found to be maximum after 6 h reaction time. It was

presumed that a small amount of acetophenone adsorbed on the acid sites

further oxidized to benzoic acid (Chumbhale et al 2005). Since the selectivity

to acetophenone was found to be maximum at 6 h reaction time, this was

chosen as the optimum condition.

113

Figure 4.1 Effect of reaction time on ethyl benzene oxidation

4.2.4 Effect of Substituents

Aerobic oxidation of ethylbenzene over PrAlPO-5 (25) at 120 oC

yielded acetophenone as the major product along with 1-phenylethanol as

minor product. The various substituents in the aromatic ring

ofethylbenzenechanged the electron density around the benzylic hydrogen

atom. As stated already the reaction proceeded via hydrogen abstraction

mechanism. The free radical formed in the proposed mechanism could be

stabilized either by electron releasing or electron withdrawing substituent.

Hence, the electron density around the benzylic hydrogen may not alter the

selectivity to form the respective carbonyl compound. The benzylic oxidation

of various substituted ethylbenzenes was attempted and the results are

presented in Table 4.2. All the substituted compounds exhibited almost

similar selectivity (> 90 %) under the given reaction conditions. Since the free

radical formed at benzylic carbon is resonance stabilized by both electron

114

releasing and electron withdrawing substituents in the para position, this

catalyst is found to be suitable for the oxidation of substituted ethylbenzene

compounds.

Table 4.2 Effect of substituents on benzylic oxidation

S.No. R1 R2 Conversion

(%)a

Selectivity

(%)

Major product

1. CH3 H 95 95 Acetophenone

2. CH3 Cl 94 94 4-Chloroacetophenone

3. CH3 Br 94 95 4-Bromoacetophenone

4. CH3 F 93 95 4-Fluoroacetophenone

5. CH3 I 91 93 4-Iodoacetophenone

6. CH3 NO2 90 94 4-Nitroacetophenone

7. H NO2 91 93 4-Nitrobenzaldehyde

8. CH3 OCH3 94 93 4-Methoxyacetophenone

9. H H 94 93 Benzaldehyde

10. H OCH3 94 94 4-Methoxybenzaldehyde

11. C6H5 H 96 95 Benzophenone

aDetermined by GC-MS

115

4.2.5 Catalyst Recycling

In order to address the problem of leaching of Pr from AlPO-5, 5 mg of fresh catalyst was dissolved in aqua regia and elemental composition was analyzed using ICP-OES. The catalyst recovered from the reaction mixture after 2 h reaction time was washed with 5% dilute nitric acid, dried and dissolved completely in aqua regia. The elemental composition of this solution was also performed using ICP-OES. The results clearly showed that praseodymium content in the catalyst before and after the reaction remained almost the same. Hence it was concluded that praseodymium remained intact in AlPO-5 and well incorporated in the framework. The recovered catalyst after the reaction was washed well with ether and dried at 200 oC. The recycled catalyst was used in the reaction for five times under the same reaction conditions. It was found that the catalyst showed similar activity up to five reaction cycles.

4.3 CONCLUSION

The hydrothermal synthesis of PrAlPO-5 with different (Al+P)/Pr ratios was successfully accomplished in the fluoride medium. The ESR study confirmed the presence of chemisorbed oxygen on the catalyst, which concluded that this catalyst is found suitable for oxidation reactions. The TPR study revealed the absence of free Pr2O3 and PrO2 which confirmed that the oxidation reaction proceeded via chemisorbed oxygen in the aerobic oxidation of ethylbenzene. The decrease of (Al+P)/Pr ratio increased the conversion and selectivity. This correlated the dependence of Pr content in AlPO-5 and reactivity. It is also concluded that the weak and moderately strong acid sites created by the framework incorporation of praseodymium in AlPO-5 favored the side chain oxidation rather than ring hydroxylation. The electron density in the aromatic ring did not influence the selectivity to acetophenone. This study also concluded that ethylbenzene and different substituted ethylbenzenes can be effectively oxidized using molecular oxygen as oxidant over PrAlPO-5 at 120 oC.

116

CHAPTER 5

SYNTHESIS OF CAMPHOLENIC ALDEHYDE

FROM -PINENE OVER PrAlPO-5

5.1 INTRODUCTION

-Pinene is a cheap and renewable source for the manufacture of

many fine chemicals (Monteiro &Velos 2004).The oxidation of -pinene

yielded products such as -pinene oxide, verbenol and verbenone, which are

key precursors for the synthesis of artificial flavors, fragrances and drugs

(Chapuis &Jacoby 2001, Calogirou et al 1999, Wender &Mucciaro, 1992).

Coelho et al (2012) used Fe-MCM-41 catalysts for the transformation of -

pinene oxide into various value-added fragrance compounds such as trans-

sobrerol, campholenic aldehyde andtrans-carveol.The product distribution

remarkably depended on the nature of solvent. Ravasio et al (2008) also

reported the isomerisation of -pinene oxide to campholenic aldehyde using

Fe (III) acetylacetonate grafted silica. In this reaction verbenone, trans-

sobrerol and trans-carveol were also formed as minor products. Since

majority of the fragrance compounds are formed by the isomerisation of -

pinene oxide, it is important to selectively oxidize -pinene to -pinene oxide.

Skrobot et al (2003) reported the oxidation of -pinene with

H2O2/ammonium acetate at room temperature and atmospheric pressure,thus

produced -pinene oxide as the main product. -Pinene co-oxidation with

isobutyraldehyde selectively afforded -pinene epoxide, with the selectivity

depended on the amount of NH2 groups on the support and attained 94% at

117

96% alkene conversion. Woitiski et al (2004) reported epoxidation of natural

terpenes using hydrogen peroxide–dinuclear manganese(IV)complex as

oxidant. Eimer et al (2008) reported -pinene oxidation over TS-1 using H2O2

as the oxidizing agent.

Ajaikumar et al (2011) reported the oxidation of -pinene over gold

containing bimetallic nanoparticles supported on reducible TiO2 using

t- butylhydroperoxide (TBHP). The copper–gold containing bimetallic

catalysts were found to be active and selective towards the formation of more

amount of verbenone than other products in the oxidation of -pinene under

liquid phase condition at mild temperatures. Allal et al (2003) explained the

allylic oxidation of -pinene to verbenol and verbenone using H2O2 and

t- butylhydroperoxide respectively. Lu et al (2009) obtained -pinene oxide as

the major product over nanosized metal oxides in the aerobic oxidation of

-pinene. TBHP was used as an initiator in the reaction. Kuznetsova et al

(2007) studied the liquid-phase oxidation of -pinene with oxygen in the

temperature range of 70–90 °C in the presence of Pd, Pt, Ru, Rh, and Ir

supported on carbon. They reported that the conversion of -pinene and the

selectivity of the main reaction products, namely, verbenol, verbenone and

-pinene oxidedepended on the nature of the metal, on its oxidation state, the

extent of metal dispersion and on the admixtures introduced into the system.

Maksimchuk et al (2005) carried out aerobic oxidation of -pinene

over cobalt-substituted polyoxometalate supported on amino-modified

mesoporous silicates. Timofeeva et al (2012) studied the -pinene oxidation

using molecular oxygen over vanadium containing nickel phosphate catalyst.

They evaluated the effect of vanadium content on the activity and selectivity

of the catalyst. Patil et al (2007) studied cobalt cation-exchanged zeolite

Ybased catalysts in the epoxidation of -pinene with molecular oxygen in the

pressure range of 20-100 psi usingN,N-dimethylformamide (DMF) as a

118

solvent at 373 K. The best results were obtained using NaCsCoY20 with 47%

-pinene conversion and 61 % epoxide selectivity at 80 psi pressure. The

solvent was observed to play an important role in the epoxidation of

-pinene, and best results were obtained in N,N-dimethylformamide as the

solvent. Lajunen (2001) explained the beneficial effect of

t- butylhydroperoxide in the catalytic epoxidation of -pinene.

It is clear from the literature that the selective oxidation of -pinene

to -pinene oxide and isomerisation of -pinene oxide to campholenic

aldehyde depends on the nature of oxidant, medium of reaction and initiators

used in the reaction. Hence, it is necessary to choose a catalyst which carries

both redox and acid property for the one pot synthesis of campholenic

aldehyde from -pinene. van der Waal et al (1996) reported bi-functional

nature of Ti4+ ions in the liquid phase Meerwein–Ponndorf–Verley (MPV)

reduction of 4-tert-butylcyclohexanone to 4-tert-butylcyclohexanol. The

isolated Ti4+ ions performed the role of both redox and acid sites.

In this chapter the catalytic activity of PrAlPO-5 (75, 100, 150 and

200) was evaluated in the synthesis of campholenic aldehyde from -pinene.

This study illustrated that PrAlPO-5 is not only a redox catalyst but also a

mild Lewis acid catalyst for the formation of isomerised products. The active

sites aided one pot synthesis of campholenic aldehyde from -pinene.


Liquid phase aerobic oxidation of -pinene was carried over

PrAlPO-5 molecular sieves in the temperature range of 30-70 oC using

chloroform as the solvent with a view to obtain selective oxidation products.

Campholenic aldehyde was found to be the major product after 12 h reaction

time whereas -pinene oxide, verbenol and verbenone were also identified as

the minor products in the liquid phase oxidation (Scheme5.1).

119

Scheme 5.1 Synthesis of campholenic aldehyde from -pinene

The influence of reaction parameters such as temperature, reaction

time, solvent and Pr content in AlPO-5 was also studied. The formation of

campholenic aldehyde exemplified the dual nature of the catalyst. -Pinene

was first converted to epoxide by the chemisorbed oxygen present on the

praseodymium sites of PrAlPO-5. The praseodymium sites also contained

Lewis acidity which in turn isomerised -pinene oxide to campholenic

aldehyde. Based on the product selectivity and the sequence of reaction,

plausible mechanism is proposed as depicted in Scheme 5.2. In this

mechanism molecular oxygen chemisorbs on the praseodymium sites and the

distant oxygen site of chemisorbed oxygen homolytically cleaves the carbon-

carbon double bond to form the radical intermediate (1). The radical

intermediate (1) rearranges to form -pinene oxide. Pr-O (2) formed during

the catalytic epoxidation of -pinene abstracts the allylic hydrogen to form

-pinenyl radical (3). This -pinenyl radical (3) acts upon by the distant

oxygen site of chemisorbed oxygen to form metal -pinene peroxide species

(5). The peroxide species (5) decompose to form -pinene oxy radical (6).

120

Scheme 5.2 Plausible pathway for the oxidation of -pinene and isomerisation of -pinene oxide

121

-Pinene oxy radical (6) abstracts allylic hydrogen of -pinene to form trans-

verbenol and -pinenyl radical (3). The trans-verbenol formed in the reaction

further oxidises by Pr-OH (4) species to form verbenone. This reaction is

essential to generate Lewis acidic Pr sites for the isomerisation of -pinene

oxide to campholenic aldehyde. PrAlPO-5 co-ordinates with epoxide oxygen

to form a carbocation (7). This six membered ring carbocation rearranges to

form less stable five membered ring carbocation (8). The campholenic

aldehyde is formed by the rearrangement of carbocation (8). The reaction

pathway is supported by the generation of campholenic aldehyde during the

latter stage of the reaction.

5.2.1 Effect of Temperature

-Pinene undergoes rapid and non-selective auto-oxidation without

any catalyst above 100 oC (Lajunen 2001). Liquid phase oxidation of

-pinene in the presence of air was carried over PrAlPO-5 (75, 100, 150 and

200) catalysts in the temperature range of 30-70 oC using chloroform as the

solvent. The experimental results are presented in Table 5.1. The -pinene

conversion and campholenic aldehyde selectivity increased with increase of

temperature. The selectivity to -pinene oxide decreased with increase of

temperature whereas selectivity to verbenol increased slightly. The reaction

temperature was maintained at 70 oC for 12 h to obtain the highest -pinene

conversion with high selectivity to campholenic aldehyde. It is concluded that

70 oC is the optimum temperature for the synthesis of campholenic aldehyde

from -pinene.

5.2.2 Effect of (Al+P)/Pr Ratios

PrAlPO-5 with different (Al+P)/Pr ratios viz. 75, 100, 150 and 200

were attempted for campholenic aldehyde synthesis and the results are

122

presented in Table 5.1. PrAlPO-5 with (Al+P)/Pr ratio 75 showed higher

selectivity to campholenic aldehyde than others at 70°C. Since Pr content in

PrAlPO-5 (75) was high, it possessed large number of Lewis acid sites. The

high concentration of Lewis acid sites increased the isomerisation of -pinene

oxide to campholenic aldehyde. -Pinene conversion also increased with

increase in praseodymium content. Hence, it is concluded that PrAlPO-5 (75)

is better than others for the synthesis of campholenic aldehyde from -pinene.

Table 5.1 Effect of reaction temperature and (Al+P)/Pr ratios on the oxidation of -pinene

Catalyst Temperature(°C)

Conversion(Wt%)

Selectivity (%)

-Pinene oxide Campholenic aldehyde Verbenol Others

20030 16 8 84 5 350 28 4 85 7 470 37 5 85 7 3

15030 27 6 86 5 350 43 3 86 6 470 51 3 87 6 4

10030 41 6 86 5 350 68 4 87 5 470 79 3 89 6 3

7530 59 6 88 4 250 78 4 89 5 270 92 3 90 5 2

Reaction condition: chloroform = 10 ml, 12 h, air (5ml/min)


The influence of reaction time on -pinene conversion and

selectivity to -pinene oxide and campholenic aldehyde was studied between

1 and 14 h over PrAlPO-5 (75) at 70 oC using chloroform as the solvent.The

results are depicted in Figure 5.1. The percentage conversion of

123

-pinene increased steadily from 1 to 12 h reaction time and thereafter

stabilized. The selectivity to -pinene oxide was found to be maximum upto

5 h reaction time which then underwent slow decomposition over Lewis acid

sites present on PrAlPO-5 (75), thus yielded campholenic aldehyde. After 5 h

reaction time the selectivity to campholenic aldehyde increased steadily at the

expense of -pinene oxide. This observation also supported the proposed

mechanism. It is evidently clear that -pinene oxide is the precursor for the

formation of campholenic aldehyde in this reaction. The selectivity to

campholenic aldehyde below 5 h reaction time is low ( 12 %) compared to

epoxide selectivity. Since the concentration of -pinene is maximum during

the initial stage of the reaction, it is oxidized by chemisorbed oxygen. When

the concentration of -pinene oxide reached considerable amount it is acted

upon by Lewis acid sites on PrAlPO-5 to form campholenic aldehyde.

Figure 5.1 Effect of reaction time

124

5.2.4 Effect of Solvents

Aerobic oxidation of -pinene was carried out at 70 °C over

PrAlPO-5 (75) using different solvents and the results are presented in Table

5.2. Among the solvents, chloroform and dichloroethane showed good

selectivity to campholenic aldehyde. Although polar solvents like acetonitrile,

acetone, dimethylacetamide enhanced the formation of -pinene oxide, these

solvents favored the isomerisation of -pinene oxide to give products like

trans-sobrerol, trans-pinocarveol and trans-carveol. Though acetonitrile

enhanced the conversion of -pinene to -pinene oxide, it decreased the

selectivity of campholenic aldehyde. trans-Pinocarveol, trans-sobrerol and

trans-carveol were also formed along with the desired product. trans-Carveol

was formed along with campholenic aldehyde when dimethylacetamide was

used as the solvent. From this study, it is concluded that polarity and basicity

of the solvents played a key role in the isomerisation of -pinene oxide

(Rocha et al 2008).

Table 5.2 Effect of solvents on the oxidation of -pinenea

Solvent Conversion

(%)b

Selectivity (%)

Campholenic

aldehyde

-Pinene

oxide

Others

Chloroform 90 91.4 7.3 1.3

Dichloroethane 81 76.7 16.7 6.6

Acetonitrile 88 37.8 12.4 49.8

Acetone 80 34.9 11.5 53.6

Dimethylacetamide 92 18.4 10.3 71.3aReaction condition: -Pinene (5 mmol), solvent:10 ml, catalyst: PrAlPO-5 (75)

(100 mg), for 12 h at 70oC. b Determined by gas chromatography.

125

5.2.5 Structure Identification of Products

The separation of the products was carried out with column

chromatography using neutral alumina (Merck) with ethyl acetate: hexane in

the ratio 1.2:10 as eluent. Nuclear magnetic resonance (NMR) spectra were

recorded on a Bruker (500 MHz) instrument using TMS as internal standard

and CDCl3 as solvent. The 1H-NMR spectra of campholenic aldehyde

(Figure 5.2), -pinene oxide (Figure 5.3) and verbenone (Figure 5.4)

confirmed the structure of the products.

126

NMR spectral data:

Campholenic aldehyde

1H NMR (500 MHz, CDCl3): 1.26 (6H, s), 1.76-1.78 (3H, s), 2.18 (1H, m),

2.43-2.47 (2H, dd), 2.56-2.57 (2H, t), 5.60-5.61(1H, t) and 9.73-9.82 (1H, t).

- Pinene oxide

1H NMR (500 MHz, CDCl3): 0.94 (3H, s), 1.29-1.33 (6H, s), 1.72-1.91

(1H, t), 1.87-1.97 (1H, m), 1.97-2.02 (4H, dd) and 2.89-3.05 (1H, t).

Verbenone

1H NMR (500 MHz, CDCl3): 1.02 (3H, s), 1.50 (3H, s), 2.02 (3H, s), 2.08-

2.45 (2H, dd), 2.62-2.65 (1H, t), 2.65-2.78 (1H, t) and 5.71 (1H, s).

130

5.2.6 Catalyst Recycling

In order to check the reusability of the catalyst, 5 mg each of fresh

and used catalyst was dissolved in aqua regia and analysed using ICP-OES.

The results showed almost same praseodymium content in the fresh and used

catalyst. The recovered catalyst after the reaction was washed with

acetonitrile and dried at 200 °C. The recycled catalyst used in the reaction

showed almost similar activity upto 5 reaction cycles. This confirmed that

leaching of Pr from AlPO-5 did not happen during the catalytic reaction. It is

confirmed that the catalyst can be used for five reaction cycles without loss of

activity.

5.3 CONCLUSION

PrAlPO-5 catalysts with different (Al+P)/Pr ratios were

successfully synthesized under hydrothermal condition in fluoride medium.

Spectroscopic and other characterization studies evidenced the incorporation

of praseodymium into AlPO-5 framework. The decrease of (Al+P)/Pr ratio

increased the conversion and selectivity to campholenic aldehyde. The

oxidation of -pinene occurred via chemisorbed oxygen on the

praseodymium sites. It is also concluded that Lewis acid sites created by the

framework incorporation of praseodymium in AlPO-5 favored the

isomerisation of -pinene oxide to campholenic aldehyde. These results

confirmed the bi-functional nature of PrAlPO-5. The weakly basic and non-

polar solvents favored the isomerisation of -pinene oxide to campholenic

aldehyde. This study concluded that campholenic aldehyde can be selectively

synthesized from -pinene over bifunctional PrAlPO-5 catalysts at 70 oC

using non-polar solvents.

131

CHAPTER 6

SYNTHESIS OF 5-ARYLIDENE-2,4-THIAZOLIDINEDIONES

OVER FeAlPO-5

6.1 INTRODUCTION

The thiazolidinediones, also known as glitazones, are a class of

drugs used in the treatment of type 2 diabetes mellitus (Bhat et al 2004).

2, 4-Thiazolidinedione (TZD) derivatives gained significant importance as

they possess various biological activities such as antimicrobial (Bonde &

Gaikwad 2004), cytotoxic (Patil et al 2010), antimalarial (Sunduru et al 2009),

antihyperglycemic (Cantello et al 1994a) and neuroprotective (Youssef et al

2010). The typical synthesis of these 2,4-thiazolidinedione analogues was

achieved by Knoevenagel condensation of aromatic aldehydes in the presence

of organic bases like triethylamine, pyridine, piperidine and more (Bruno et al

2002, Zask et al 1990, Cantello et al 1994b). These low molecular weight

organic amines are known to exhibit toxic effect to the human beings. Since

the reaction is catalyzed by both acid and base, it could be possible to

synthesis TZD derivatives using solid acid catalysts.

Several solid acid catalysts were reported as environmental friendly

catalysts in the synthesis of many organic compounds. Reddy et al (2001)

reported the synthesis of substituted coumarins by the reactions of resorcinol

and substituted resorcinol with ethyl acetoacetate and ethyl

-methylacetoacetate (Pechmann reaction). The production of

environmentally harmful waste streams is minimized by the use of novel solid

132

acid catalyst in this reaction. Huang & Fu (2013) summarized recent advances

in the hydrolysis of cellulose by different types of solid acids such as

sulfonated carbonaceous based acids, polymer based acids and magnetic solid

acids. The acid strength, acid site density, adsorption of the substrate and

micropores of the solid material are the key factors for effective hydrolysis

processes. Shimizu and Satsuma (2011) reviewed the role of solid acid

catalysts in the biomass conversion and Friedel-Crafts acylation reaction.

Saravanamurugan et al (2005) studied the liquid phase Claisen–

Schmidt condensation between 2’-hydroxyacetophenone and benzaldehyde to

form 2’-hydroxychalcone, followed by intramolecular cyclisation to form

flavanone over zinc oxide supported metal oxide catalysts under solvent free

condition. Saravanamurugan et al (2004) also studied the reaction of

2’-hydroxyacetophenone with benzaldehyde over H-ZSM-5, Mg-ZSM-5 and

Ba-ZSM-5 catalysts at 140 °C. The products were 2-hydroxychalcone and

flavanone. They also studied the role of solvents to enhance the conversion.

Recently, Pachamuthu et al (2013) reported Mannich type reactions

over SnTUD-1 materials. SnTUD-1 with interesting Lewis acidity provided

excellent activities in the one-pot three-component Mannich-type reactions of

ketones with aldehydes and amines at room temperature. They reported the

synthesis of a range of -aminocarbonyl compounds in moderate to very good

yields under very mild reaction conditions. However, green synthesis of TZD

derivatives using solid acid catalysts is not reported so far.

Iron incorporated AlPO-5 molecular sieves have unique catalytic

properties and are widely used as promising catalysts in many reactions (Shiju

et al 2006, Hentit et al 2007 and Cheng et al 2012). In this study, the

hydrothermal synthesis of FeAlPO-5 with Fe/Al ratios of 75, 100 and 150

molecular sieves in the presence of fluoride ions were found to be

catalytically active in the synthesis of 5-arylidene-2, 4-thiazolidinedione

133

analogues. Various substituted benzaldehydes were allowed to react with

2, 4-thiazolidinedione in order to understand the effect of electron density in

the synthesis of TZD analogues. It was found that the reusable solid acid

catalyst could replace the role of toxic mineral acids, organic and inorganic

bases in the TZD analogue synthesis.


The nature and type of acid sites and chemical location of iron in

FeAlPO-5 were well established by various characterization techniques. The

catalytic activity of FeAlPO-5 was evaluated in the Knoevenagel

condensation of substituted aldehydes with 2,4-thiazolidinedione using water-

ethanol (4:1) mixture as solvent (Scheme 6.1).

Scheme 6.1 Synthesis of 5-arylidene-2,4-thiazolidinedione

Knoevenagel condensation was catalysed by both Bronsted and

Lewis acid sites (Rao & Venkataratnam 1991, Bao et al 1996, Wang et al

1997). The catalytic activity study was focused to design a greener route for

the synthesis of 5-arylidene-2,4-thiazolidinedione. Though the reaction

proceeded faster in polar solvents like dimethyl sulphoxide, acetonitrile and

ethanol, the reaction parameters such as temperature, iron content and

reaction time were optimized in water-ethanol solvent system with a view to

design a greener route for the synthesis of TZD derivatives. The general

mechanism for the condensation of aldehyde with activated methylene group

is depicted in Scheme 6.2.

134

Scheme 6.2 Plausible mechanism for the synthesis of water mediated TZD derivative

The reaction initiates with protonation of carbonyl oxygen of

aldehyde by Bronsted acid sites generated by the interaction of water with

135

Lewis acid sites, thus facilitates the carbonyl carbon of the aldehyde

vulnerable to nucleophilic attack. Similar protonation of 2,4-thiazolidinedione

yields enolic form which in turn attacked the carbonyl carbon. The desired

product is formed by subsequent elimination of water molecule. The reaction

exhibits significant product yield in aprotic solvents as presented in

Scheme 6.3. The carbonyl group can also be activated by Lewis acid sites

itself.

Scheme 6.3 Plausible mechanism – The role of Lewis acid sites in the synthesis of TZD derivative

136

The Lewis acid sites co-ordinate with carbonyl group and facilitate

the nucleophilic attack on the carbonyl carbon. This was confirmed by using

polar aprotic solvent as medium. The aromatic aldehydes are least soluble in

water and hence a small quantity of ethanol was used in the reaction mixture

when solid aromatic aldehydes were used in the reaction. The influence of

electron density in the synthesis of 5-arylidene-2,4-thiazolidinedione was also

studied.

6.2.1 Effect of Temperature and Al/Fe Ratios

Synthesis of 5-benzylidene-2,4-thiazolidinedione was carried in the

liquid phase over FeAlPO-5 (75, 100 and 150) catalysts in the temperature

range 30-100 oC using water-ethanol as solvent for 8 h reaction time. The

conversion of aldehyde increased with increase of temperature while the yield

of 5-benzylidene-2,4-thiazolidinedione was above 95 % at all temperatures.

The reaction was monitored with TLC. After 8 h reaction time the catalyst

was separated from the reaction mixture by filtration, and the organic layer

was extracted with ethyl acetate and dried over anhydrous sodium sulphate.

The organic layer was vaccum distilled and column purified over silica gel of

60-120 mesh using 20 % ethyl acetate in hexane. The isolated product yield

and the amount of unreacted starting material were calculated and presented

in Table 6.1. The reaction reached a maximum conversion of 98.5 % at 100 oC

over FeAlPO-5 (75) catalyst. The FeAlPO-5 (75) possessed larger number of

acid sites than the other two catalysts, which clearly demonstrated that

increase in acidity increased the aldehyde conversion. Hence, it is concluded

that FeAlPO-5 (75) is better than other catalysts for the synthesis of 5-

benzylidene-2,4-thiazolidinedione by Knoevenagel condensation of

benzaldehyde and 2,4-thiazolidinedione. The structural identification of the

compound was confirmed by 1H-NMR.

137

Table 6.1 Effect of reaction temperature and Al/Fe ratios in the synthesis of 5-benzylidene - 2, 4 – thiazolidinedione

Catalyst Temperature

(°C)

Conversion

(Wt %)

Isolated product yield

(Wt %)

P1 Others

150

30 20.8 96.5 3.5

70 41.5 97.3 2.7

100 53.4 97.5 2.5

100

30 41.9 97.7 2.3

70 69.7 98.2 1.8

100 80.7 98.5 1.5

75

30 59.6 98.6 1.4

70 87.5 98.8 1.2

100 98.5 98.8 1.2

Reaction condition: Solvent: Water-ethanol (4:1) = 5 ml & Reaction time: 8 h

P1: 2,4-Thiazolidinedione


The influence of reaction time on benzaldehyde conversion and

selectivity to 5-benzylidene-2,4-thiazolidinedione was studied between 1 and

10 h over FeAlPO-5 (75) at 100 oC using water-ethanol as the solvent. The

results are depicted in Figure 6.1. The percentage conversion of benzaldehyde

increased steadily from 1 to 8 h reaction time and then stabilized. The isolated

product yield of 5-benzylidene-2,4-thiazolidinedione was above 95 % till the

end of the reaction time. Beyond 8 h reaction time, there was no further

increase in the percentage conversion of benzaldehyde.

138

Figure 6.1 Effect of reaction time

6.2.3 Effect of Solvents

The nature of solvent played significant role in the synthesis of

5-benzylidene-2,4-thiazolidinedione. The effect of various solvents in the

synthesis was studied and the results are presented in Table 6.2. Polar solvents

like DMSO and DMF chemisorbed on the acid sites of FeAlPO-5, and the

protonated form of DMSO or DMF (Drexler & Amiridis 2003) favored the

polarization of carbonyl group and facilitated the condensation reaction.

Water and ethanol also favored the condensation but not as fast as in the case

of DMSO. Non-polar solvents like chloroform and dichloroethane suppressed

the polarization of carbonyl group and thus retarded the condensation

reaction. Water and ethanol in the ratio 4:1 showed relatively high conversion

than other solvents except DMSO. Though DMSO exhibited better

139

conversion than water-ethanol mixture, it was not chosen as the solvent

system for the synthesis of 5-benzylidene-2,4-thiazolidinedione as this solvent

is not ecofriendly. Water-ethanol (4:1) mixture was opted as solvent since this

could be a greener method for the synthesis of TZD analogues.

Table 6.2 Effect of solvents in the synthesis of 5-benzylidene-2,4- thiazolidinedione

Solvent Conversion

(Wt %)

Product yield (Wt %)

P1 Others

Chloroform# 59.5 97.4 2.6

Dichloroethane# 63.8 95.7 4.3

DMSO *97.8 98.7 1.3

DMF *97.5 98.1 1.9

Water 96.5 98.5 1.5

Ethanol# *97.2 97.1 2.9

Water-Ethanol(4:1) 98.5 98.8 1.2

Reaction condition: Benzaldehyde (5 mmol), 2,4 – thiazolidinedione (5 mmol),

solvent: 5 ml, catalyst: 100 mg of FeAlPO-5 (75), Reaction time: 8 h at 70 oC. #Reaction mixture refluxed, *Maximum conversion reached before 8 h,

P1: 2,4-Thiazolidinedione

6.2.4 Effect of Substituents

The reaction was carried out with various substituted

benzaldehydes using FeAlPO-5 (75) in water-ethanol solvent system at

100 °C to understand the influence of various substituents on the benzene ring

which is also considered as an important parameter in this reaction. The

effect of different substituted benzaldehydes, piperonal and heterocyclic

aldehydes on the conversion and yield of the product are presented in Table

6.3. All p-substituted benzaldehydes showed moderate to high yield of

140

5-arylidene-2,4-thiazolidinedione irrespective of their electron density

whereas o-substituted benzaldehyde showed slightly low product yield

(70%). This is attributed to steric hindrance in the ortho position. All the

p-substituted benzaldehydes showed almost maximum conversion and

product yield upto 98%. The optimized reaction conditions were applied for

the synthesis of 5-((benzo[d][1,3]dioxol-6-yl)methylene)thiazolidine-2,4-

dione by condensing piperonal and TZD over FeAlPO-5 (75). This

condensation yielded 93% product. This compound is used as a precursor for

many biologically active compounds (Chinthala et al 2013). The reaction of

thiophene-2-carbaldehyde and pyridine-3-carbaldehyde with

2,4-thiazolidinedione resulted 95% aldehyde conversion and selectivity

above 90%. It is concluded that FeAlPO-5 catalyst can be

utilized for the synthesis of 5-substituted TZD analogues.

142

6.2.5 Structure Identification of Products

The separation of the products was carried out with column chromatography using silica gel of 60-120 mesh (Merck) and ethyl acetate: hexane (2:10) as eluent. Nuclear magnetic resonance (NMR) spectra were recorded on a Bruker (500 MHz) instrument using TMS as an internal standard and DMSO-d6/CDCl3 as the solvent. The chemical shifts are reported in ppm. The 1H-NMR spectra of various 5-arylidene-1,3-thiazolidine-2,4-dione analogues are shown in figures 6.2 to 6.9

NMR spectral data: 5-(4-Nitrobenzylidene)-1-3-thiazolidine-2,4-dione

1H NMR (500 MHz, DMSO - d6): 7.29 (1H, s), 7.63-7.64 (2H, d), 8.36-8.37 (2H, d) and 10.19 (1H, s) 5-(3-Nitrobenzylidene)-1-3-thiazolidine-2,4-dione

1H NMR (500 MHz, CDCl3): 7.27-7.29 (1H, s), 7.70-7.73 (1H, m), 7.82-7.84 (1H, m), 8.30 (1H, m), 8.31-8.39 (1H, m) and 8.89 (1H, s). 5-(3-Methoxybenzylidene)-1,3-thiazolidine-2,4-dione

1H NMR (500 MHz, DMSO - d6): 3.80-3.81 (3H, s), 7.05-7.08 (1H, d), 7.14-7.17 (1H, s), 7.42-7.47 (1H, m), 7.75-7.78 (1H, s) and 12.63 (1H, s)

143

5-(2-Hydroxy-3-methoxybenzylidene)-1-3-thiazolidine-2,4-dione

1H NMR (500 MHz, DMSO - d6): 3.84 (3H, s), 6.92-6.95 (1H, m), 7.08-7.10

(2H, m), 8.05 (1H, s), 9.72 (1H, s) and 12.63 (1H, s)

5-(4-Methoxybenzylidene)-1,3-thiazolidine-2,4-dione

1H NMR (500 MHz, DMSO - d6): 3.34-3.35 (3H, s), 6.91-6.93 (2H, d), 7.45-

7.47 (2H, d), 10.31 (1H, s) and 12.63 (1H, s)

5-((Benzo[d][1,3]dioxol-6-yl)methylene)1,3-thiazolidine-2,4-dione

1H NMR (500 MHz, DMSO - d6): 6.08 (2H, s), 6.90-6.93(1H, d), 6.97 (1H,

s), 7.03-7.06 (1H, d) and 7.67 (1H, s)

144

5-((Thiophen-2-yl)methylene)thiazolidine-2,4-dione

1H NMR (500 MHz, DMSO - d6): 7.13-7.19 (1H, m), 7.61(1H, s), 7.71-7.77

(1H, d) and 7.87-7.93(1H, d)

5-((Pyridin-3-yl)methylene)thiazolidine-2,4-dione

1H NMR (500 MHz, DMSO - d6): (7.33 1H, t), 7.75 (1H, s), 7.88-7.91 (1H,

d), 8.07-8.08 (1H, d), 8.25 (1H, s) and 9.97 (1H, s)

153

6.3 CONCLUSION

FeAlPO-5 with different Al/Fe ratios were successfully synthesized

under hydrothermal condition in fluoride medium. The isomorphic

substitution of iron in MO4 tetrahedra of AlPO-5 was confirmed by ESR and

DRS-UV-Vis studies. The framework incorporation of Fe created mild acid

sites which were found to be useful in the synthesis of TZD derivatives.

Further, the reaction was carried out in water-ethanol solvent system as a

greener route for the synthesis of TZD analogues although DMSO and DMF

were found to facilitate the condensation more easily. This Lewis acidic

material is also under investigation for the synthesis of ciproflaxacin

analogues.

154

CHAPTER 7

SUMMARY AND CONCLUSION

7.1 SUMMARY AND CONCLUSION OF THE PRESENT WORK

Catalysis is one of the most important tools of green chemistry as it

minimises waste production in chemical reactions. Conventional synthesis of

fine chemicals and pharmaceuticals utilizes stoichiometric equivalents of

homogeneous catalyst such as mineral acids or Lewis acid catalysts. Selective

oxidation reactions are pivotal transformation in organic synthesis which

generates huge amount waste and the disposal is an environmental issue.

Many of these transformations are currently performed both in the laboratory

and industrial scale by the use of hazardous stoichiometric inorganic oxidants

like Cr(VI) and Mn(VI) reagents. These acid and redox catalysts generate

large amount of inorganic wastes. Further, the catalyst separation and reuse,

disposable of the spent catalyst, corrosion and toxicity are series issues which

lead to unfavourable ecological conditions. Solid acids find important

application as heterogeneous catalyst. The surface area of the catalyst is an

important factor because it increases the catalytic activity by exposing more

active centers. Bronsted and Lewis acid sites present act as active sites in

zeolites and zeotype molecular sieves. The linkage of SiO4, AlO4, PO4 and

other cations tetrahedra decides the framework shape and final structure type

of zeolites and zeo-type molecular sieves.

The discovery of aluminophosphate (zeotypes) molecular sieves

(AlPOs) widened the scope to tailormade neutral framework.However, the

155

drawback of AlPO isits neutral zeotype. The incorporation of desirable

heteroatom created active sites for several organic transformations. The

framework incorporated PrAlPO-5 with different (Al+P)/Pr ratios were

synthesized using appropriate precursors for aluminium, phosphorous and

praseodymium in fluoride medium. The catalytic activity was evaluated in the

oxidation of ethylbenzene and synthesis of campholenic aldehyde. Similarly,

iron incorporated AlPO-5 molecular sieves with different Al/Fe ratios were

synthesized and the catalytic activity was evaluated in the synthesis of

biologically active 2,4-thiazolidinedione analogues. The summary and

conclusions drawn from the study are delineated below.

The hydrothermal synthesis of PrAlPO-5 with different (Al+P)/Pr

ratios viz., 25, 50, 75, 100, 150 and 200 was successfully accomplished in

fluoride medium.The characterization using XRD, DRS-UV-vis,BET, and 27Al and 31P MAS-NMR techniques confirmed the incorporation of Pr in

AlPO-5 framework.

The phase purity of PrAlPO-5 molecular sieves was confirmed by

correlating the XRD patterns of PrAlPO-5 andXRD patterns of Pr6O11. The

lattice parameters calculated for PrAlPO-5 were different from the parent

AlPO-5. PrAlPO-5 showed higher surface area and pore volume than AlPO-5.

All these observations confirmed the incorporation of praseodymium into the

framework.The DRS-UV-Vis, ESR and XPS studiesexplained the electronic

environment of praseodymium in PrAlPO-5. The appearance of two bands

around 210 and 262 nm in DRS-UV-Vis spectra of PrAlPO-5 confirmed the

presence of Pr3+ and Pr4+species in tetrahedral environment. Further, the

absence of peak between 415 and 590 nm in PrAlPO-5 confirmed the absence

of extra-framework praseodymium species. The TPR-H2trace of PrAlPO-5

also confirmed the absence of praseodymium oxide species.The low

temperature ESR studies confirmed the chemisorption of oxygen on

156

paramagnetic praseodymium speciesand unsymmetrical environment of

praseodymium. The XPS spectrum of PrAlPO-5 confirmed the existence of

praseodymium in +3 and +4 oxidation states. The incorporation of

praseodymiumsubstitution both Al and P in TO4tetrahedra was evidently

proved from 27Al and 31P MAS-NMR spectra of PrAlPO-5. The SEM and

TEM images established the presence of inter-particle voids in PrAlPO-5. The

TPD-NH3studyand the ex-situ pyridine adsorbed IR spectra revealed the

nature and strength of acidty. Thus, the presence of both redox and acid sites

in PrAlPO-5 was established. TGA and FT-IR spectra of PrAlPO-5 confirmed

the complete removal of template.

The liquid phase aerobic oxidation of ethylbenzene over PrAlPO-5

with different (Al+P)/Pr ratios (25, 50, 75 and 100) demostrated thatthe

conversion of ethylbenzene and selectivity to acetophenone increased in the

order: PrAlPO-5 (25) > PrAlPO-5 (50) > PrAlPO-5 (75) > PrAlPO-5 (100).

Thisstudy also concluded that weak and moderately strong acid sites favoured

side chain oxidation rather than ring hydroxylation. PrAlPO-5 (25) showed

slightly higher selectivity to acetophenone (95%) and ethylbenzene

conversion (95%) at 120 °C. The substituted ethylbenzenes alteredthe electron

density around the benzylic hydrogen atom.Since benzylic oxidation was

ascribed byhydrogen abstraction of the C-H bond, the electron density around

benzylic hydrogen did not alter the selectivity to form the respective carbonyl

compound.

PrAlPO-5 with different (Al+P)/Pr ratios viz., 75, 100, 150 and 200

were attempted in the synthesis of campholenic aldehyde from -pinene. The

catalytic activity of the catalysts increased in the order:PrAlPO-5 (75) >

PrAlPO-5 (100) > PrAlPO-5 (150) > PrAlPO-5 (200). The effect of reaction

parameters such as reaction temperature, (Al+P)/Pr ratio, reaction time and

solvent were optimised over PrAlPO-5 (75) for the synthesis of campholenic

157

aldehyde. The catalyst was found to play dual role both as redox and acid

catalyst. The oxidation of -pinene occurred via chemisorbed oxygen on the

praseodymium sites.The campholenic aldehyde formation was attributed to

the isomerisation of -pinene oxide over Lewis acid sites of PrAlPO-5. This

study concluded that weakly basic and non-polar solvents favoured the

formation of campholenic aldehyde. This study also established the bi-

functional nature of PrAlPO-5 catalysts.

The hydrothermal synthesis of FeAlPO-5 with different Al/Fe

ratios (75, 100 and 150)was successfully accomplished in the fluoride

medium.The characterizationof the materials using XRD, DRS-UV-vis,BET,

SEM, ESR, XPS, TPD-NH3 and ex-situ pyridine adsorbed IR revealed the

physico-chemical characteristics of the materials.

The powder XRD patterns of FeAlPO-5catalysts displayed

characteristic reflections of AlPO-5, which were indexed to P6cc space group.

The increase of unit cell parameter from 11.51 to 11.82Å with increase of Fe

contentwas explained on the basis of atomic radius of Al and Fe. The atomic

radius of Fe3+ (0.49 Å) is larger than Al3+ (0.39 Å), assuming the coordination

number of both the atoms as four.This led to large Fe-O distance which

ultimately changed the unit cell constant of the materials. Moreover, these

observations suggested that Fe atoms were successfully incorporated into

AlPO-5 framework. FeAlPO-5 samples exhibited type I nitrogen adsorption-

desorption isotherms characteristics of microporous material. TheUV-Vis

DRS spectra of FeAlPO-5 samples revealed that most of the Fe atoms in

AlPO-5 framework occupied tetrahedral position, which was further

confirmed from the results obtained from ESR spectroscopy. The TPD-

NH3study and ex-situ pyridine adsorbed IR spectra revealed the presence of

mild Lewis acidic nature in FeAlPO-5.

158

The catalytic activity of FeAlPO-5 catalysts with different Al/Fe

ratios was tested in the Knoevenagel condensation of aromatic aldehydes with

2,4-thiazolidinediones. The catalytic activity of the catalysts increased in the

order: FeAlPO-5 (75) > FeAlPO-5 (100) > FeAlPO-5 (150). The reaction

parameters such as reaction temperature, reaction time and solvent were

optimised with FeAlPO-5 (75) for high conversion and selectivity. The

Knoevenagel condensation of several substituted benzaldehydes and

heterocyclic aldehydes with 2,4-thiazolidinedione under optimised reaction

conditions using water-ethanol (4:1) mixture as solvent was successful. This

study revealed that FeAlPO-5 is a good catalyst for green synthesis of a range

of TZD analogues.

7.2 SCOPE FOR FUTURE WORK

The present investigation results concluded that Pr incorporated

AlPO-5is a convenient eco-friendly redox catalyst for aerobic oxidation of

alkyl aromatics. PrAlPO-5 can be used not only as a redox catalyst but also

solid acid catalyst. The bi-functional nature of PrAlPO-5 catalyst will open

new prospect for potential application in the synthesis of fine chemicals.

Further, it is also confirmed that FeAlPO-5 is an efficient catalyst for the

Knoevenagel condensation. With suitable modifications and reaction

conditions, it is expected these materials can be exploited for other organic

transformations. Synthesis of ciprofloxacin analogues using FeAlPO-5 is in

the pipeline.

159

REFERENCES

1. Abu-Zied, BM & Soliman, SA 2008, ‘Thermal decomposition of praseodymium acetate as a precursor of praseodymium oxide catalyst’, Thermochimica Acta, Vol. 470, no. 1-2, pp. 91-97.

2. Ajaikumar, S, Ahlkvist, J, Larsson, W, Shchukarev, A, Leino, AR, Kordasand, K & Mikkola, JP 2011, ‘Oxidation of -pinene over gold containing bimetallic nanoparticles supported on reducible TiO2 by deposition-precipitation method’, Applied Catalysis A: General, Vol. 392, no. 1-2, pp. 11-18.

3. Akolekar, DB & Ryoo, R 1996, ‘Titanium incorporated ATS and AFI type aluminophosphate molecular sieves’, Journal of the Chemical Society, Faraday Transactions, vol. 92, no. 22, pp. 4617-4621.

4. Allal, BA, Firdoussi, LE, Allaoud, S, Karim, A, Castanet, Y & Mortreux, A 2003, ‘Catalytic oxidation of -pinene by transition metal using t-butyl hydroperoxide and hydrogen peroxide’, Journal of Molecular Catalysis A: Chemical, Vol. 200, no. 1-2, Pages 177-184.

5. Anastas, PT & Warner, JC 1998, Green chemistry theory and practise, Oxford University Press, New York.

6. Araujo, AS, Aquino, JMFB, Souza, MJB & Silva AOS 2003, ‘Synthesis, characterization and catalytic application of cerium-modified MCM-41, Journal of Solid State Chemistry’, Vol. 171, no. 1-2, pp. 371-374.

7. Araujo, AS, Diniz, JC, Silva, AOS & Melo, RAA 1997, ‘Hydrothermal synthesis of Cerium Aluminophosphate’, Journal of Alloys and Compounds, vol. 250, no. 1-2, pp. 532-537.

8. Auroux, A & Gervasini, A 1990, ‘Microcalorimetric study of the acidity and basicity of metal oxide surfaces’, The Journal of Physical Chemistry, vol. 94, no. 16, pp. 6371-6379.

160

9. Bao, W, Zhang, Y & Wang, J 1996, ‘Aldol Condensation of -Diketones and -Ketoesters with Aldehydes Catalyzed by Samarium (III) Iodide’, Synthetic Communications, Vol. 26, no. 16, pp. 3025-3028.

10. Barrer, RM, 1983, Hydrothermal Chemistry of Zeolites, Academic Press, London, pp. 121-156.

11. Barrer, RM, Bisio, A & Olson, DH (eds.) 1984, ‘Proceedings of sixth international conference on zeolites’, Butterworth, UK, pp. 870-876.

12. Barrera, A, Fuentes, S, Viniegar, M, Avalos-Borja, M, Bogdanchikova, N & Molina, JC 2007, Structural properties of Al2O3–La2O3 binary oxides prepared by sol–gel, Materials Research Bulletin, Vol. 42, no. 4, pp. 640-648.

13. Barrett, EP, Joyner, LG & Halend, PP 1951, ‘The determination of pore volume and area distributions in porous substances. I. Computation from nitrogen isotherms’, Journal of the American Chemical Society, Vol. 73, no. 1, pp. 373-380.

14. Bennett, JM, Cohen, JP, Flanigen, EM, Pluth, JJ & Smith, JV 1983, ‘Intrazeolite chemistry’, American Chemical Society Symposium Series, vol. 218, pp. 109-118.

15. Bennett, JM, Dytrch, WJ, Pluth, JJ, Richardson, JW & Smith, JV 1986, ‘Structural features of aluminophosphate materials with AlP = 1’, Zeolites, Vol. 6, no. 5, pp. 349-360.

16. Bhargaba, G, Gouzman, I, Chun, CM, Ramanarayanan, TA & Bernasek, SL 2007, ‘Characterization of the “native” surface thin film on pure polycrystalline iron: A high resolution XPS and TEM study’, Applied Surface Science, Vol. 253, no. 9, pp. 4322-4329.

17. Bhat, BA, Ponnala, S, Sahu, DP, Tiwari, P, Tripathi, BK & Srivastava, AK 2004, ‘Synthesis and antihyperglycemic activity profiles of novel thiazolidinedione derivatives’, Bioorganic & Medicinal Chemistry, Vol. 12, no. 22, pp. 5857-5864.

18. Bonde, CG & Gaikwad, NJ 2004, ‘Synthesis and preliminary evaluation of some pyrazine containing thiazolines and thiazolidinones as antimicrobial agents’, Bioorganic & Medicinal Chemistry, Vol. 12, no. 9, pp. 2151-2161.

161

19. Breck, DW 1964, ‘Crystalline Molecular sieves’, Journal of Chemical Education, vol. 41, no. 12, pp. 678-689.

20. Brunauer, S, Emmett, PH & Teller, E 1938, ‘Adsorption of gases in multimolecular layers’, Journal of the American Chemical Society, Vol. 60, no. 2, pp. 309-319.

21. Bruno, G, Costantino, L, Curinga, C, Maccari, R, Monforte, F, Nicolo, F, Ottana, R & Vigorita, MG 2002, ‘Synthesis and aldose reductase inhibitory activity of 5-arylidene-2,4-thiazolidinediones’, Bioorganic & Medicinal Chemistry, Vol. 10, no. 4, pp. 1077-1084.

22. Calogirou, A, Larsen, BR & Kotzias, D 1999, ‘Gas-phase terpene oxidation products: a review’, Atmospheric Environment, Vol. 33, no. 9, pp. 1423-1439.

23. Cantello, BCC, Cawthorne, MA, Cottam, GP, Duff, PT, Haigh, D, Hindley, RM, Lister, CA, Smith, SA & Thurlby, PL 1994, ‘[[o-(Heterocyclylamino)alkoxy]benzyl]-2,4-thiazolidinediones as Potent Antihyperglycemic Agents’, Journal of Medicinal Chemistry, vol. 37, no. 23, pp. 3977-3985.

24. Cantello, BCC, Cawthorne, MA, Haigh, D, Hindley, RM, Smith, SA & Thurlby, PL 1994, ‘The synthesis of BRL 49653 - a novel and potent antihyperglycaemic agent’, Bioorganic & Medicinal Chemistry Letters, Vol. 4, no. 10, pp. 1181-1184.

25. Carnall, WT, Goodman, GL, Rajnak, K & Rana, RS 1989, ‘A systematic analysis of the spectra of the lanthanides doped into single crystal LaF3’, The Journal of Chemical Physics, vol. 90, no. 7, pp. 3443-3457.

26. Catana, G, Pelgrims, J & Schoonheydt, RA 1995, ‘Electron spin resonance study of the incorporation of iron in ferrisilicalite and FAPO-5’, Zeolites, Vol. 15, no. 5, pp. 475-480.

27. Chapuis, C & Jacoby, D 2001, ‘Catalysis in the preparation of fragrances and flavours’, Applied Catalysis A: General, Vol. 221, no. 1-2, pp. 93-117.

28. Cheetham, AK, Férey, G & Loiseau, T 1999, ‘Open-framework inorganic materials’, Angewandte Chemie, vol. 38, no. 22, pp. 3268-3292.

162

29. Chen, J, Pang, W & Xu, R 1999, ‘Mixed-bonded open-framework aluminophosphates and related layered materials’, Topic in Catalysis. vol. 9, no. 1-2, pp. 93-103.

30. Chen, J, Thomas, JM & Sankar, G 1994, ‘IR spectroscopic study of CD3CN adsorbed on ALPO-18 molecular sieve and the solid acid catalysts SAPO-18 and MeAPO-18’, Journal of the Chemical Society, Faraday Transactions, vol. 90, no. 22, pp. 3455-3459.

31. Chen, JD & Sheldon, RA 1995, ‘Selective Oxidation of Hydrocarbons with O2 over Chromium Aluminophosphate-5 Molecular-Sieve’, Journal of Catalysis, Vol. 153, no. 1, pp. 1-8.

32. Chen, JD, Lempers, HEB & Sheldon, RA 1996, ‘Synthesis, characterization and catalytic oxidation of alcohols with chromium-substituted aluminophosphates’, Journal of the Chemical Society, Faraday Transactions, vol. 92, pp. 1807-1813.

33. Cheng, DG, Chen, F and Zhan, X 2012, ‘Characterization of iron-containing AlPO-5 as a stable catalyst for selective catalytic reduction of N2O with CH4 in the presence of steam’, Applied Catalysis A: General, Vol. 435-436, pp. 27-31.

34. Cheralathan, KK, Kannan, C, Palanichamy, M & Murugesan, V 2000, ‘Ethylation of toluene over aluminophosphate based molecular sieves in the vapour phase’, Indian Journal of Chemistry section A-Inorganic Bio-Inorganic Physical Theoretical & analytical chemistry, vol. 39, pp. 921-927.

35. Chinthala, Y, Domatti, AK, Sarfaraz, A, Singh, SP, Arigari, NK, Gupta, N, Satya, SKVN, Kumar, JK Khan, F, Tiwari, AK & Paramjit, G 2013, ‘Synthesis, biological evaluation and molecular modeling studies of some novel thiazolidinediones with triazole ring’, European Journal of Medicinal Chemistry, Vol. 70, pp. 308-314.

36. Chumbhale, VR, Paradhy, SA, Anilkumar, M, Kadam, ST & Bokade, VV 2005, ‘Vapour Phase Oxidation of Acetophenone to Benzoic Acid Over Binary Oxides of V and Mo’, Chemical Engineering Research and Design, Vol. 83, no. 1, pp. 75-80.

37. Coelho, JV, de Meireles, ALP, da Silva Rocha, KA, Pereira, MC, Oliveira, LCA and Gusevskaya, EV 2012, ‘Isomerization of -pinene oxide catalyzed by iron-modified mesoporous silicates’, Applied Catalysis A: General, Volumes 443-444, pp. 125-132.

163

38. Concepcion, P, Nieto, JML, Mifsud, A & Pariente, JP 1997, ‘Synthesis, characterization and catalytic properties of microporous MgVAPO-5’, Applied Catalysis A: General, vol. 151, no. 2, pp. 373-392.

39. Cooper, ER, Andrews, CD, Wheatley, PS, Webb, PB, Wormald, P & Morris, RE 2004, ‘Ionic liquids and eutectic mixtures as solvent and template in synthesis of zeolite analogues’, Nature, vol. 430, no. 7003, pp. 1012-1016.

40. Corà, F & Catlow, CRA 2001, ‘Ionicity and framework stability of crystalline aluminophosphates’, Journal of Physical Chemistry B, vol. 105, no.42, pp. 10278-10281.

41. da Silva Rocha, KA, Hoehne, JL & Gusevskaya, EV 2008, ‘Phosphotungstic Acid as a Versatile Catalyst for the Synthesis of Fragrance Compounds by -Pinene Oxide Isomerization: Solvent-Induced Chemoselectivity’, Chemistry - A European Journal, Vol. 14, no. 20, pp. 6166-6172.

42. Davis, ME & Lobo, RF 1992, ‘Zeolite and molecular sieve syntheses, Chemistry of Materials, vol. 4, no. 4, pp. 756-768.

43. Davis, ME, Saldarriaga, C, Montes, C, Carcer, J & Crowder, C 1988, ‘A molecular sieve with eighteen-membered rings’, Nature, vol. 331, no. 6158, pp. 698-699.

44. Devika, S, Palanichamy, M & Murugesan, V 2011, ‘Selective oxidation of ethylbenzene over CeAlPO-5’, Applied Catalysis A: General, vol. 407, no. 1-2, pp. 76-84.

45. Devika, S, Palanichamy, M & Murugesan, V 2012, ‘Selective Oxidation of Diphenylmethane to Benzophenone over CeAlPO-5 Molecular Sieves’, Chinese Journal of Catalysis, Vol. 33, no. 7-8, pp. 1086-1094.

46. Donega, CDM, Meijerink, A & Blasse, G 1995, ‘Non-radiative relaxation processes of the Pr3+ ion in solids’, Journal of Physics and Chemistry of Solids, Vol. 56, no. 5, pp. 673-685.

47. Dorenbos, P 2000, ‘The 4f n 4f n 15d transitions of the trivalent lanthanides in halogenides and chalcogenides’, Journal of Luminescence, Vol. 91, no. 1-2, pp. 91-106.

164

48. Drexler, MT & Amiridis, MD 2003, ‘The effect of solvents on the heterogeneous synthesis of flavanone over MgO’, Journal of Catalysis, Vol. 214, no. 1, pp. 136-145.

49. Dumitriu, E, Guimon, C, Hulea, V, Lutic, D & Fechete, I 2002, ‘Transalkylation of toluene with trimethylbenzenes catalyzed by various AFI catalysts’, Applied Catalysis A: General, vol. 237, no. 1-2, pp. 211-221.

50. Eimer, GA, Díaz, I. Sastre, E, Casuscelli, SG, Crivello, ME. Herrero, ER & Pariente, JP 2008, ‘Mesoporous titanosilicates synthesized from TS-1 precursors with enhanced catalytic activity in the -pineneselective oxidation’, Applied Catalysis A: General, vol. 343, no. 1-2, pp. 77-86.

51. Elangovan, SP & Murugesan, V 1997, ‘Catalytic transformation of cyclohexanol over aluminophosphate-based molecular sieves’, Journal of Molecular Catalysis A: Chemical, vol. 118, no. 3, pp. 301-309.

52. Fang, M, Du, HB, Xu, WG, Meng, XP & Pang, WQ 1997, ‘Microwave preparation of molecular sieve AlPO4-5 with nanometer sizes’, Microporous Materials, Vol. 9, no. 1-2, pp. 59-61.

53. Flanigen, EM 1976, Zeolite Chemistry and Catalysis, ACS Monograph 171, Washington D. C., p. 231-241, 1976.

54. Flanigen, EM, Lok, BM, Patton, RL & Wilson, ST 1986, ‘Aluminophosphate molecular sieves and the periodic table’, Studies in Surface Science Catalysis, vol. 28, pp. 103-112.

55. Flanigen, EM, Patton, RL, Wilson, ST & Gorbert, PJ (eds.), Innovation in Zeolite Material Science, Elsevier Amsterdam.

56. Gielgens, LH, Veenstra, IHE, Ponec, V, Haanepen, MJ & van Hooff, JHC 1995, ‘Selective isomerisation of n-butene by crystalline aluminophosphates’, Catalysis Letters, vol. 32, no. 1-2, pp. 195-203.

57. Goldfarb, D, Bernardo, M, Strohmaier, KG, Vaughan, DEW & Thomann, H 1994, ‘Characterization of Iron in Zeolites by X-band and Q-Band ESR, Pulsed ESR, and UV-Visible Spectroscopies’, Journal of the American Chemical Society, vol. 116, no. 14, pp. 6344-6353.

165

58. Guo, CC, Chu, MF, Liu, Q, Liu, Y, Guo, DC & Liu, XQ 2003, ‘Effective catalysis of simple metalloporphyrins for cyclohexane oxidation with air in the absence of additives and solvents’, Applied Catalysis A: General, Vol. 246, no. 2, pp. 303-309.

59. Guo, Z, Guo, C, Jin, Q, Li, B & Ding, D 2005, ‘Synthesis and Structure of Large AlPO4-5 Crystals’, Journal of Porous Materials, Vol. 12, no. 1, pp. 29-33.

60. Hartmann, M & Kevan, L 1999, ‘Transition-metal ions in aluminophosphate and silicoaluminophosphate molecular sieves: Location, interaction with adsorbates and catalytic properties’, Chemical Reviews, vol. 99, no. 3, pp. 635-664.

61. Hentit, H, Bachari, K, Ouali, MS, Womes, M, Benaichouba, B & Jumas, JC 2007, ‘Alkylation of benzene and other aromatics by benzyl chloride over iron-containing aluminophosphate molecular sieves’, Journal of Molecular Catalysis A: Chemical, vol. 274, no. 1-2, pp. 158-166.

62. Hsu, BY and Cheng, S 1998, ‘Pinacol rearrangement over metal-substituted aluminophosphate molecular sieves’, Microporous Mesoporous Material, vol. 21, no. 4-6, pp. 505-515.

63. Huang, Q & Hwu, SJ 1999, ‘Cs2Al2P2O9: An exception to Löwenstein’s rule. Synthesis and characterization of a novel layered aluminophosphate containing linear Al-O-Al linkages’, Chemical Communications, no. 23, pp. 2343-2344.

64. Huang, X, Wang, L, Kong, L & Li, Q 2003, ‘Improvement of catalytic properties of SAPO-11 molecular sieves synthesized in H2O–CTAB–butanol system’, Applied Catalysis A: General, Vol. 253, no. 2, pp. 461-467.

65. Huang, YB & Fu, Y 2013, ‘Hydrolysis of cellulose to glucose by solid acid catalysts’, Green Chemistry, vol. 15, no. 5, pp. 1095-1111.

66. Huo, Q, Xu, R, Li, S, Ma, Z, Thomas, JM, Jones, RH & Chippindale, AM 1992, ‘Synthesis and characterization of a novel extra large ring of aluminophosphate JDF-20’, Journal of Chemical Society, Chemical Communications, no.12, pp. 875-876.

166

67. Ishii, Y & Sakaguchi, S 2006, ‘Recent progress in aerobic oxidation of hydrocarbons by N-hydroxyimides’, Catalysis Today, vol. 117, no. 1-3, pp. 105-113.

68. Kanjina, W & Trakarnpruk, W 2010, ‘Oxidation of Cyclohexane and Ethylbenzene by Hydrogen Peroxide over Co-substituted Heteropolytungstate Catalyst’, Journal of Metals, Materials and Minerals, Vol. 20, No. 2, pp. 29-34.

69. Kanjina, W & Trakarnpruk, W 2011, ‘Mixed metal oxide catalysts for the selective oxidation of ethylbenzene to acetophenone’, Chinese Chemical Letters, vol. 22, no. 4, pp. 401-404.

70. Kannan, C, Elangovan, SP, Palanichamy, M & Murugesan, V 1998, ‘Ethylation of toluene over aluminophosphate molecular sieves in the vapour phase’, Indian Journal of Chemical Technology, vol. 5, pp. 65-68.

71. Kawai, M, Tsukada, M & Tamaru, K 1981, ‘Surface electronic structure of binary metal oxide catalyst ZrO2/SiO2’, Surface Science, vol. 111, no. 2, pp. L716-L720.

72. Kuznetsova, LI, Kuznetsova, NI, Lisitsyn, AS, Beck, IE, Likholobov, VA & Ancel, JE 2007, ‘Liquid-phase oxidation of -pinene with oxygen catalyzed by carbon-supported platinum metals’, Kinetics and Catalysis, Vol. 48, no. 1, pp. 38-44.

73. Lajunen, MK 2001, ‘Co(II) catalysed oxidation of -pinene by molecular oxygen: Part III’, Journal of Molecular Catalysis A: Chemical, , vol. 169, no. 1-2, pp. 33-40.

74. Levi, Z, Raitsimring, AM & Goldfarb, D 1991, ‘ESR and electron spin-echo studies of MnAlPO-5’, Journal of Physical Chemistry, vol. 95, no. 20, pp. 7830-7838.

75. Lewis, DW, Catlow, CRA & Thomas, JM 1996, ‘Influence of organic templates on the structure and on the concentration of framework metal ions in microporous aluminophosphate catalysts’, Chemistry of Material, vol. 8, no. 5, pp. 1112-1118.

76. Li, HX & Davis, ME 1993, ‘Further studies on aluminophosphate molecular sieves. Part 1.-AlPO4-H2: a hydrated aluminophosphate molecular sieve’, Journal of the Chemical Society, Faraday Transactions, vol. 89, pp. 957-964.

167

77. Li, J, Li, X, Shi, Y, Mao, D & Lu, G 2010, ‘Selective oxidation of cyclohexane by oxygen in a solvent-free system over lanthanide-containing AlPO-5’, Catalysis Letters, vol. 137, no. 3-4, pp. 180-189.

78. Lin, SS & Weng, HS 1993, ‘Liquid-phase oxidation of cyclohexane using CoAPO-5 as the catalyst’, Applied Catalysis A: General, vol. 105, no. 2, pp. 289-308.

79. Liu, P, Ren, J & Sun, Y 2008, ‘Influence of template on Si distribution of SAPO-11 and their performance for n-paraffin isomerization’, Microporous and Mesoporous Materials, Vol. 114, no. 1-3, pp. 365-372.

80. Lohse, U, Bertram, R, Jancke, L, Kurzawski, I, Parlitz, B, Löuffler, E & Schreier, E 1995, ‘Acidity of aluminophosphate structures. Part 2.-Incorporation of cobalt into CHA and AFI by microwave synthesis’, Journal of Chemical Society, Faraday Transition, vol. 91, no. 8, pp. 1163-1172.

81. Lohse, U, Noack, M & Jahn, E 1987, ‘Adsorption properties of the aluminium phosphate (AlPO-5) molecular sieve’, Adsorption Science & Technology, vol. 3, pp. 19-24.

82. Lok, BM, Cannan, TR & Messina, CA 1983, ‘The role of organic molecules in molecular sieve synthesis’, Zeolites, vol. 3, no.4, pp. 282-291.

83. Lok, BM, Messina, CA, Patton, RL, Gajek, RT, Cannan, TR & Flanigen EM 1984, ‘Silicoaluminophosphate molecular sieves: another new class of microporous crystalline inorganic solids’, Journal of American Chemical Society, vol. 106, no. 20, pp. 6092-6093.

84. Löwenstein, W 1954, ‘The distribution of aluminium in the tetrahedra of silicates and aluminates’, American Mineralogiest, vol. 39, no. 1-2, pp. 92-94.

85. Lu, JM, Ranjit, KT, Rungrojchaipan, P & Kevan, L 2005, ‘Synthesis of Mesoporous Aluminophosphate (AlPO) and Investigation of Zirconium Incorporation into Mesoporous AlPOs’, The Journal of Physical Chemistry B, vol. 109, no.19, pp. 9284-9293.

168

86. Lu, XH, Xia, QH, Fang, SY, Xie, B, Qi, B & Tang, ZR 2009, ‘Highly Selective Epoxidation of -Pinene and Cinnamyl Chloride with Dry Air over Nanosized Metal Oxides’, Catalysis Letters, Vol. 131, no. 3-4, pp. 517-525.

87. Maksimchuk, NV, Melgunov, MS, Mrowiec-Bia on, J, Jarzebski, AB & Kholdeeva, OA 2005, ‘H2O2-based allylic oxidation of -pineneover different single site catalysts’, Journal of Catalysis, Vol. 235, no. 1, pp. 175-183.

88. Mal, NK & Ramaswamy, AV 1996, ‘Oxidation of ethylbenzene over Ti-, V- and Sn-containing silicalites with MFI structure’, Applied Catalysis A: General, Vol. 143, no. 1, pp. 75-85.

89. Mal, NK, Ramaswamy, V, Gonaphathy, S & Ramaswamy, AV 1995, ‘Synthesis of tin-silicalite molecular sieves with MEL structure and their catalytic activity in oxidation reactions’, Applied Catalysis A: General, Vol. 125, no. 2, pp. 233-245.

90. Ma ecka, MA & Kepinski, L 2007, ‘Solid state reactions in highly dispersed praseodymium oxide–SiO2 system’, Journal of Alloys and Compounds, Vol. 430, no. 1-2, Pages 282-291.

91. Maurelli, S, Vishnuvarthan, M, Berlier, G & Chiesa, M 2012, ‘NH3 andO2 interaction with tetrahedral Ti3+ ions isomorphously substituted in the framework of TiAlPO-5. A combined pulse EPR, pulse ENDOR, UV-Vis and FT-IR study’, Physical Chemistry Chemical Physics, vol. 14, no. 2, pp. 987-995.

92. McBain, JW 1932, The sorption of gases and vapours by solids, G. Rutledge & sons, London.

93. Meier, WM & Olson, DH 1987, Atlas of Zeolite Structure Types, Butterworth, London.

94. Merrouche, A, Patarin, J, Kessler, H, Soulard, M, Delmotte, L, Guth, JL & Joly, JF 1992, ‘Synthesis and characterisation of cloverite: a novel gallophosphate molecular sieve with three-dimensional 20-membered ring channels’, Zeolites, vol. 12, no. 3, pp. 226-232.

95. Monteiro, JLF & Velos, CO 2004, ‘Catalytic Conversion of Terpenes into Fine Chemicals’, Topics in Catalysis, Vol. 27, no. 1-4, pp. 169-180.

169

96. Montes, C, Davis, ME, Murray, B & Narayana, M 1990, ‘Isolated redox centers within microporous environments. 1. Cobalt-containing aluminophosphate molecular sieve five’, Journal of Physical Chemistry, vol. 94, no.16, pp. 6425-6430.

97. Pachamuthu, MP, Shanthi, K, Luque, R & Ramanathan, A 2013, ‘SnTUD-1: a solid acid catalyst for three component coupling reactions at room temperature’, Green Chemistry, vol. 15, no. 8, pp. 2158-2166.

98. Parida, KM and Dash, SS 2009, ‘Manganese containing MCM-41: Synthesis, characterization and catalytic activity in the oxidation of ethylbenzene’, Journal of Molecular Catalysis A: Chemical, vol. 306, no. 1-2, pp. 54-61.

99. Parnham, ER, Wheatley, PS & Morris, RE 2006, ‘The ionothermal synthesis of SIZ-6 - a layered aluminophosphate’, Chemical Communications, no. 4, pp. 380-382.

100. Pastore, HO, Coluccia, S & Marchese, L 2005, ‘Porous aluminophosphates: From molecular sieves to designed acid catalysts’, Annual Review of Materials Research, vol. 35, pp. 351-395.

101. Patil, MV, Yadav, MK & Jasra, RV 2007, ‘Catalytic epoxidation of -pinene with molecular oxygen using cobalt(II)-exchanged zeolite Y-based heterogeneous catalysts’, Journal of Molecular Catalysis A: Chemical, vol. 277, no. 1-2, pp.72-80.

102. Patil, V, Tilekar, K, Munj, SM, Mohan, R & Ramaa, CS 2010, ‘Synthesis and primary cytotoxicity evaluation of new 5-benzylidene-2,4-thiazolidinedione derivatives’, European Journal of Medicinal Chemistry, Vol. 45, no. 10, pp. 4539-4544.

103. Perego, G, Bellussi, C, Corno, M, Taramasso, F, Buonomo, F, Esposito, A & Murakami Y (eds.) 1986, ‘New developments in Zeolite science and technology’, Elsevier, Amsterdam, pp. 129-138.

104. Perkas, N, Wang, Y, Koltypin, Y, Gedankenand, A & Chandrasekaran, S 2001, ‘Mesoporous iron–titania catalyst for cyclohexane oxidation’, Chemical Communications, no. 11, pp. 988-989.

105. Piera, E, Miguel, A, Saloman, Coronas, J, Menedez, M & Santamaria, J 1998, ‘Synthesis Characterisation and separation techniques of a composite mordenite/ZSM-5/Chabazite hydrophilic membrane’, Journal of Membrane Science, vol. 149, no. 1, pp. 99-114.

170

106. Prakash, AM, Satyanarayana, CVV, Ashtekar, S & Chakrabarthy, DK 1994, ‘SAPO-46 molecular sieve: Incorporation of silicon at crystallographically independent sites’, Journal of Chemical Society, Chemical Communications, no. 13, pp. 1527-1528.

107. Pujado, PR, Rabo, JA, Antos, GJ & Gembicki, SA 1992, ‘Industrial catalytic applications of molecular sieves’, Catalysis Today, vol. 13, no. 1, pp. 113-141.

108. Pujado, PR, Rabo, JA, Antos, GJ & Genbicki, SA 1992, ‘Industrial catalytic applications of molecular sieves’, Catalysis Today, Vol. 13, no. 1, pp. 113-141.

109. Rabo, JA, Angell, CL, Kasai, PH & Schomarker, V 1966, ‘Acid function in zeolites recent progess’, Discussions of the Faraday Society, vol. 41, no. 1, pp. 328-331.

110. Radhika, T & Sugunan, S 2007, ‘Vanadia supported on ceria: Characterization and activity in liquid-phase oxidation of ethylbenzene’, Catalysis Communications, Vol. 8, no. 2, pp. 150-156.

111. Rajabi, F, Luque, R, Clark, JH, Karimi, B & Macquarrie, DJ 2011, ‘A silica supported cobalt (II) Salen complex as ef cient and reusable catalyst for the selective aerobic oxidation of ethyl benzene derivatives’, Catalysis Communications, vol. 12, no. 6, pp. 510-513.

112. Raju, G, Reddy, PS, Ashok, J, Reddy, BM & Venugopal, A 2008, ‘Solvent-free aerobic oxidation of ethylbenzene over supported Ni catalysts using molecular oxygen at atmospheric pressure’, Journal of Natural Gas Chemistry, vol. 17, no.3, pp. 293-297.

113. Rao, PS & Venkataratnam, RV 1991, ‘Zinc chloride as a new catalyst for knoevenagel condensation’, Tetrahedron Letters, Vol. 32, no. 41, pp. 5821-5822.

114. Ravasio, N, Zaccheria, F, Gervasini, A & Messi, C. 2008, ‘A new, Fe based, heterogeneous Lewis acid: Selective isomerization of -pineneoxide’, vol. 9, no. 6, pp. 1125–1127.

115. Reddy, BM, Reddy, VR & Giridar, D 2001, ‘synthesis of coumarins catalyzed by eco-friendly W/ZrO2 solid acid catalyst’, Synthetic Communications, vol. 31, no. 23, pp. 3603-3607.

171

116. Reddy, KR, Ramaswamy, AV & Ratnasamy, P 1993, ‘Studies on Crystalline Microporous Vanadium Silicates: IV. Synthesis, Characterization, and Catalytic Properties of V-NCL-1, a Large-Pore Molecular-Sieve’, Journal of Catalysis, Vol. 143, no. 1, Pages 275-285.

117. Saravanamurugan, S, Palanichamy, M, Arabindoo, B & Murugesan, V 2004, ‘Liquid phase reaction of 2 -hydroxyacetophenone and benzaldehyde over ZSM-5 catalysts’, Journal of Molecular Catalysis A: Chemical, Vol. 218, no. 1, pp. 101-106.

118. Saravanamurugan, S, Palanichamy, M, Arabindoo, B & Murugesan, V 2005, ‘Solvent free synthesis of chalcone and flavanone over zinc oxide supported metal oxide catalysts’, Catalysis Communications, Vol. 6, no. 6, pp. 399-403.

119. Selvam, P & Mohapatra, SK 2006, ‘Thermally stable trivalent iron-substituted hexagonal mesoporous aluminophosphate (FeHMA) molecular sieves: Synthesis, characterization, and catalytic properties’, Journal of Catalysis, Vol. 238, no. 1, pp. 88-99.

120. Selvam, T & Singh, AP 1995, ‘Single step selective oxidation of para-chlorotoluene to para-chlorobenzaldehyde over vanadium silicate molecular sieves’, Journal of the Chemical Society, Chemical Communications, no. 8, pp. 883-884.

121. Sheldon, RA & van Bekkum, H 2001, Fine Chemicals through Heterogeneous Catalysis, Wiley-VCH, Germany.

122. Shiju, NR, Fiddy, S, Sonntag, O, Stockenhuber, M & Sankar, G 2006, ‘Selective oxidation of benzene to phenol over FeAlPO catalysts using nitrous oxide as oxidant’, Chemical Communications, no. 47, pp. 4955-4957.

123. Shimizu, K & Satsuma, A 2011, ‘Toward a rational control of solid acid catalysis for green synthesis and biomass conversion’, Energy & Environmental Science, vol. 4, no. 9, pp. 3140-3153.

124. Sing, KSW, Everett, DH, Haul, RA, Moscou, WL, Pierotti, RA, Rouquerol, J & Siemieniewska, T 1985, Reporting Physisorption Data For Gas/Solid Systems With Special Reference To The Determination Of Surface Area And Porosity, International Union Of Pure And Applied Chemistry, vol. 57, no. 4, pp. 603-619.

172

125. Singh, PS, Kosuge, K, Ramaswamy, V & Rao, BS 1999, ‘Characterization of MeAPO-11s synthesized conventionally and in the presence of fluoride ions and their catalytic properties in the oxidation of ethylbenzene’, Applied Catalysis A: General, vol. 177, no. 2, pp. 149-159.

126. Skrobot, FC, Valente, AA, Neves, G, Rosa, I, Rocha, J & Cavaleiro, JAS 2003, ‘Monoterpenes oxidation in the presence of Y zeolite-entrapped manganese(III) tetra(4-N-benzylpyridyl)porphyrin’, Journal of Molecular Catalysis A: Chemical, Vol. 201, no. 1-2, pp. 211-222.

127. Smil, V 1999, ‘Detonator of the population explosion’, Nature, vol. 400, no. 6743, pp. 415.

128. Soria, MA, Perez, P, Carabineiro, SAC, Hodar, FJM, Mendes, A & Madeira, LM 2014, ‘Effect of the preparation method on the catalytic activity and stability of Au/Fe2O3 catalysts in the low-temperature water–gas shift reaction’, Applied Catalysis A: General, Vol. 470, pp. 45-55.

129. Stach, H, Thamn, H, Fielder, K, Grauet, B, Weiker, W & Jahn, E 1986, New Developments in Zeolites Science and Technology, Elsevier, Amsterdam.

130. Subrahmanyam, C, Louis, B, Rainone, F, Viswanathan, B, Renken, A & Varadarajan, TK 2002, ‘Partial oxidation of toluene by O2 over mesoporous Cr-AlPO’, Catalysis Communication, vol. 3, pp. 45-50.

131. Subrahmanyam, C, Louis, B, Viswanathan, B, Renken, A & Varadarajan, TK 2005, ‘Synthesis, characterisation and catalytic properties of vanadium substituted mesoporous aluminophosphates’, Applied Catalysis A: General, vol. 282, no. 1-2, pp. 67-71.

132. Subrahmanyam, C, Viswanathan, B & Varadarajan, TK 2004, ‘Synthesis, characterization and catalytic activity of mesoporous trivalent iron substituted aluminophosphates’, Jornal of Molecular Catalysis A: Chemical, vol. 223, no. 1-2, pp. 149-153.

133. Sunduru, N, Srivastava, K, Rajakumar, S, Puri, SK, Saxena, JK & Chauhan, PMS 2009, ‘Synthesis of novel thiourea, thiazolidinedione and thioparabanic acid derivatives of 4-aminoquinoline as potent antimalarials’, Bioorganic & Medicinal Chemistry Letters, Vol. 19, no. 9, pp. 2570-2573.

173

134. Suresh, BW, Saha, SK, Kubota, Y & Sugi, Y 2004, ‘Isopropylation of benzene with 2-propanol over AFI alumino-phosphate molecular sieves substituted with alkaline earth metal’, Journal of Catalysis, vol. 228, no. 1, pp. 192-205.

135. Szostak, R 1989, Molecular Sieves Principles of Synthesis and Identification, van Nostrand Reinhold, New York.

136. Tankov, I, Pawelec, B, Arishtirova, K & Damyanova, S 2011, ‘Structure and surface properties of praseodymium modified alumina’, Applied Surface Science, Vol. 258, no. 1, pp. 278-284.

137. Thomas, JM 1999, ‘Design, synthesis and in situ characterization of new solid catalysts’, Angewadte Chemie, vol. 38, no.24, pp. 3588-3628.

138. Thomas, JM, Raja, R, Sankar, G & Bell, RG 1999, ‘Molecular sieve catalysts for the selective oxidation of linear alkanes by molecular oxygen’, Nature, vol. 398, no. 6724, pp. 227-230.

139. Thomas, JM, Raja, R, Sankar, G & Bell, RG 2001, ‘Molecular sieve catalysts for the regioselective and shape selective oxyfunctionalization of alkanes in air’, Account of Chemical Research, vol. 34, no.3, pp. 191-200.

140. Tian, P, Liu, Z, Wu, Z, Xu, L & He, Y 2004, ‘Characterization of metal-containing molecular sieves and their catalytic properties in the selective oxidation of cyclohexane’, Catalysis Today, vol. 93-95, pp. 735-742.

141. Timofeeva, MN, Hasan, Z, Panchenko, VN, Prosvirin, IP & Jhung, SH 2012, ‘Vanadium-containing nickel phosphate molecular sieves as catalysts for -pinene oxidation with molecular oxygen: A study of the effect of vanadium content on activity and selectivity’, Journal of Molecular Catalysis A: Chemical, vol. 363-364, pp. 328-334.

142. Tomita, T, Nakayama, K, & Sakai, H, 2004, ‘Gas separation characteristics of DDR type zeolite membrane’, Micorporous and Mesoporous Materials, vol. 68, no. 1-3, pp. 71-75.

174

143. Trojan, KL, Kendall, JL, Kepler, KD & Hatfield, WE 1992, ‘Strong exchange coupling between the lanthanide ions and the phthalocyaninato ligand radical in bis(phthalocyaninato)lanthanide sandwich compounds’, Inorganica Chimica Acta, Vol. 198-200, pp. 795-803.

144. Trost, BM 1991, ‘The atom economy: A search for synthetic efficiency’, Science, vol. 254, pp. 1471-1477.

145. Trost, BM 1995, ‘Atom economy - A challenge for organic synthesis: Homogeneous catalysis leads the way’, Angewandte Chemie, vol. 34, no. 3, pp. 259-281.

146. Tusar, NN, Laha, SC, Cecowski, S, Arcon, I, Kaucic, V and Glaser, R 2011, ‘Mn-containing porous silicates as catalysts for the solvent-free selective oxidation of alkyl aromatics to aromatic ketones with molecular oxygen’, Microporous and Mesoporous Materials, Vol. 146, no. 1-3, pp. 166-171.

147. Umamaheswari, V, Kannan, C, Arabindo, B, Palanichamy, M & Murugesan, V 2000, ‘Isomorphous substitution of Mn(II), Ni(II) and Zn(II) in AlPO-31 molecular sieves and study of their catalytic performance’, Journal of Chemical Sciences, Vol. 112, no. 4, pp. 439-448.

148. Uytterhoeven, JB, Christner, LG & Hall, WK 1965, ‘Studies of the Hydrogen held by Solids: VIII. The Decationated Zeolites’, The Journal of Physical Chemistry B, vol. 69, no. 6, pp. 2117-2126.

149. van der Waal, JC, Tan, K & van Bekkum, H 1996, ‘Zeolite titanium beta: a selective and water resistant catalyst in Meerwein-Ponndorf-Verley-Oppenauer reactions’, Catalysis Letters, Vol. 41, no. 1-2, pp. 63-67.

150. Vijayaraghavan, VR & Raj, KJA 2004, ‘Ethylation of benzene with ethanol over substituted large pore aluminophosphate-based molecular sieves’, Journal of Molecular Catalysis A: Chemical, vol. 207, no. 1, pp. 41-50.

151. Vomscheid, R, Briend, M, Peltre, MJ, Man, PP & Barthomeuf, D 1994, ‘The role of the template in directing the Si distribution in SAPO zeolites’, Journal of Physical Chemistry, vol. 98, no. 38, pp. 9614-9618.

175

152. Wang, LM, Tian, BZ, Fan, J, Liu, XY, Yang, HF, Yu, CZ, Tu, B & Zhao, DY 2004, ‘Block copolymer templating syntheses of ordered large-pore stable mesoporous aluminophosphates and Fe-aluminophosphate based on an “acid–base pair”’, Microporous and Mesoporous Materials, Vol. 67, no. 2-3, pp. 123-133.

153. Wang, N, Tang, ZK, Li, GD & Chen, JS 2000, ‘Materials science: Single-walled 4 Å carbon nanotube arrays’, Nature, vol. 408, no. 6808, pp. 50-51.

154. Wang, QL, Ma, Y, Zuo, BJ 1997, ‘Knoevenagel Condensation Catalyzed by USY Zeolite’, Synthetic Communications, vol. 27, no. 23, pp. 4107-4110.

155. Wei, W, Moulijn, JA & Mul, G 2008, ‘Effect of steaming of iron containing AlPO-5 on the structure and activity in N2Odecomposition’, Microporous and Mesoporous Materials, Vol. 112, no. 1-3, pp. 193-201.

156. Wender, PA & Mucciaro, TP 1992, ‘A new and practical approach to the synthesis of taxol and taxol analogs: the pinene’, Journal of the American Chemical Society, vol. 114, no. 14, pp. 5878-5879.

157. Wentzel, BB, Donners, MPJ, Alsters, PL, Feiters, MC & Nolte, RJM 2000, ‘N-Hydroxyphthalimide/Cobalt(II) Catalyzed Low Temperature Benzylic Oxidation Using Molecular Oxygen’, Tetrahedron, vol. 56, no. 39, pp. 7797-7803.

158. Wilson, ST 1991, ‘Synthesis of AlPO4,-based molecular sieves’, Studies in Surface Science and Catalysis, vol. 58, pp. 137-151.

159. Wilson, ST 2001, ‘Chapter 5B Phosphate-based molecular sieves: Novel synthetic approaches to new structure and compositions’, Studies in Surface Science and Catalysis, vol. 137, pp. 229-260.

160. Wilson, ST, Lok, BM & Flanigen, EM 1982a, Crystalline metallophosphate compositions, US Patent 4310440.

161. Wilson, ST, Lok, BM, Messina, CA, Cannan, TR & Flanigen, EM 1982, ‘Aluminophosphate molecular sieves: A new class of microporous crystalline inorganic solids’, Journal of American Chemical Society, vol. 104, no. 4, pp. 1146-1147.

176

162. Woitiski, CB, Kozlov, YN, Mandelli, D, Nizova, GV, Schuchardt, U & Shul’pin, GB 2004, ‘Oxidations by the system “hydrogen peroxide–dinuclear manganese(IV) complex–carboxylic acid”: Part 5. Epoxidation of olefins including natural terpenes’, Journal of Molecular Catalysis A: Chemical, Vol. 222, no. 1-2, pp. 103-119.

163. Yadav, GD & Thorat, TS 1996, ‘Role of benzyl ether in the inversion of reactivities in Friedel-Crafts benzylation of toluene by benzyl chloride and benzyl alcohol’, Tetrahedron Letters, vol. 37, no. 30, pp. 5405-5408.

164. Yadav, GD, Thorat, TS & Kumbhar, PS 1993, ‘Inversion of the relative reactivities and selectivities of benzyl chloride and benzyl alcohol in Friedel-Crafts alkylation with toluene using different solid acid catalysts: An adsorption related phenomenon’, Tetrahedron Letters, vol. 34, no. 3, pp. 529-532.

165. Yamashita, T & Hayes, P 2008, ‘Analysis of XPS spectra of Fe2+ and Fe3+ ions in oxide materials’, Applied Surface Science, Vol. 254, no. 8, pp. 2441-2449.

166. Youssef, AM, White, MS, Villanueva, EB, ElAshmawy, IM & Klegeris, A 2010, ‘Synthesis and biological evaluation of novel pyrazolyl-2,4-thiazolidinediones as anti-inflammatory and neuroprotective agents’, Bioorganic & Medicinal Chemistry, Vol. 18, no. 5, pp. 2019-2028.

167. Yu, C, Ge, Q, Xu, H & Li, W 2006, ‘Effects of Ce addition on the Pt-Sn/ -Al2O3 catalyst for propane dehydrogenation to propylene’, Applied Catalysis A: General, Vol. 315, pp. 58-67.

168. Yu, J & Xu, R 2003, ‘Rich structure chemistry in the aluminophosphate family’, Accounts of Chemical Research, vol. 36, no. 7, pp. 481-490.

169. Zahedi-Niaki, MH, Zaidi, SMJ & Kaliaguine, S 2000, ‘Comparative study of canadium aluminophosphate molecular sieves VAPO-5, -11, -17 and -31’, Applied Catalysis A: General, vol. 196, no. 1, pp. 9-24.

170. Zask, A, Jirkovsky, I, Nowicki, JW & McCaleb, ML 1990, Synthesis and antihyperglycemic activity of novel 5-(naphthalenylsulfonyl)-2,4-thiazolidinediones, Journal of Medicinal Chemistry, vol. 33, no. 5, pp. 1418-1423.

177

171. Zecchina, A & Arean, CO 1996, ‘Diatomic molecular probes for mid-IR studies of zeolites’, Chemical Society Reviews, vol. 25, no. 3, pp. 187-197.

172. Zhan, W, Guo, Y, Wang, Y, Liu, X, Guo, Y, Wang, Y, Zhang, Z & Lu, G 2007, ‘Synthesis of Lanthanum-Doped MCM-48 Molecular Sieves and Its Catalytic Performance for the Oxidation of Styrene’, The Journal of physical Chemistry B, vol. 111, no. 42, pp 12103-12110.

173. Zhao, R, Wang, Y, Guo, Y, Guo, Y, Liu, X, Zhang, Z, Wang, Y, Zhan, W & Lu, G 2006, ‘A novel Ce/AlPO-5 catalyst for solvent-free liquid phase oxidation of cyclohexane by oxygen’, Green Chemistry, vol. 8, pp. 459-466.

174. Zones, SI, Nakagawa, Y, Yuen, LT & Harris, TVJ 1996, ‘Guest/hostinteractions in high silica zeolite synthesis: [5.2.1.02.6]tricyclodecanesas template molecule’, Journal of American Chemical Society, vol. 118, no. 32, pp. 7558-7567.

178

LIST OF PUBLICATIONS

1. Sundaravel, B, Babu, CM, Palanisamy, B, Palanichamy, M, Shanthi, K & Murugesan, V 2013, ‘Praseodymium incorporated AlPO-5 molecular sieves for aerobic oxidation of ethylbenzene’, Journal of Nanoscience and Nanotechnology, Vol. 13, pp. 2507-2516.

2. Sundaravel, B, Babu, CM, Palanisamy, B, Palanichamy, M & Murugesan, V 2014, ‘Green synthesis of 5-arylidene-2,4-thiazolidinediones over FeAlPO-5 catalysts’, Advanced Porous Materials (Accepted)

3. Visuvamithiran, P, Sundaravel, B, Palanichamy, M & Murugesan, V 2013, ‘Oxidation of alkyl aromatics over SBA-15 supported cobalt oxide’, Journal of Nanoscience and Nanotechnology, Vol. 13, pp. 2528-2537.

4. Babu, CM, Palanisamy, B, Sundaravel, B, Palanichamy, M & Murugesan, V 2013, ‘A novel magnetic Fe3O4/SiO2 core-shell nanorods for the removal of arsenic’, Journal of Nanoscience and Nanotechnology, Vol. 13, pp. 2517-2527.

5. Venkatachalam, K, Visuvamithiran, P, Sundaravel, B, Palanichamy, M & Murugesan, V 2012, ‘Catalytic performance of Al-MCM-48 molecular sieves for isopropylation of phenol with isopropyl acetate’, Chinese Journal of Catalysis, Vol. 33, pp. 478-486.

6. Devika, S, Sundaravel, B, Palanichamy, M & Murugesan, V 2013, ‘Vapour phase oxidation of toluene over cerium substituted AlPO-5 molecular sieves’, Journal of Nanoscience and Nanotechnology (Accepted).

179

CONFERENCES

1. Sundaravel, B., Visuvamithiran, P., Palanichamy M. and Murugesan, V. “Allylic oxidation of cycloalkene over CeFeAlPO-5”, International Conference on Frontiers in Materials Science for Energy and Environment, LIFE, Loyola College, Chennai, January 11-13, 2012.

2. Sundaravel, B., Palanichamy M. and Murugesan, V. “Liquid phase aerobic oxidation of ethylbenzene over PrAlPO-5 catalysts”, 21st National Symposium on Catalysis for Sustainable Development, CSIR-Indian Institute of Chemical Technology, Hyderabad, February 11-13, 2013.

3. Sundaravel, B., Visuvamithiran, P., Palanichamy M. and Murugesan, V. “Aerobic oxidation of cycloalkene over CeFeAlPO-5”, National Conference on Interface between Chemical Sciences and Technologies, National Institute of Technology, Warangal, December 29-30, 2011.

4. Sundaravel, B., Devika, S., Visuvamithiran, P., Palanichamy M. and Murugesan, V. “Chemoselective oxidation of dialkyl aromatics over Ce-AlPO-5 ”, 15th National Workshop on The Role of New materials in Catalysis, Indian Institute of Technology, Chennai, December 11-13, 2011.

5. Visuvamithiran, P., Sundaravel, B., Palanichamy, M. and Murugesan, V. “Aerobic chemoselective oxidation of alkyl aromatics over Fe3O4@Ag core- shell nanoparticle”, International Conference on Frontiers in Nanoscience and Nanotechnology and their Applications, Panjab University, Chandigarh, February 16-18, 2012.

praseodymium and iron incorporated alpo-5...

Documents