devaki nandan 2015
TRANSCRIPT
SYNTHESIS OF POROUS CARBON COMPOSITES AND
METAL OXIDES FOR CATALYTIC APPLICATIONS
Thesis Submitted to AcSIR for the Award of
the Degree of
DOCTOR OF PHILOSOPHY
in
Chemistry
By
Devaki Nandan
(Enrollment No. 10CC11J19012)
Under the guidance of Dr. Nagabhatla Viswanadham, Principal Scientist
Refining Technology Division
CSIR-Indian Institute of Petroleum Dehradun -248 005,
Uttarakhand, India
February 2015
Dedicated
To My parents,
wife, brother and our daughter
Disha
Acknowledgements
Ph. D. Thesis of Mr. Devaki Nandan CSIR-IIP
First and foremost, I thank my supervisor, Dr. Nagabhatla Viswanadham. During my
tenure, he rewarded me by giving intellectual freedom in my work, engaging me in
new ideas, and demanding a high quality of work in all my endeavors.
I would like to thanks Director, Indian Institute of Petroleum, Dr. M. O. Garg for
allowing me to utilize the facilities of IIP and permitting me to submit my research
work in the form of thesis.
Besides my advisor, I would like to thank my Doctoral Advisory Committee
(DAC) members, Dr. A. K. Chatterjee, Dr. S. M. Nanoti, Dr. O. P. Khatri, and
Dr. V. V. D. N Prasad for their encouragement, inspiring discussions and
suggestions throughout the research work.
In addition, I also express my sincere thanks to Mr. S. K. Ganguly, AcSIR-IIP
coordinator, for his valuable support and also thankful to Dr. A. K. Jain,
DAC coordinator and Shaloo Vanodhia Madam, for helping me at any time
throughout my stay in IIP.
The faculty members of course work Dr. B. Sain, Dr. Y. K. Sharma, Dr. S. L. Jain, are
thankful to giving me knowledge to complete course work.
I also express my sincere gratitude to all the members of analytical division of IIP
specially Mr. S. Saran for XRD, Dr. Manoj Kumar for porosimetry, Mr. S. K.
Konathala for SEM, Dr. Pankaj K. Kanaujia and Mr. D. Tripathi for GC-MS, Mr. G.
M. Bahuguna and Mr. R. Singh for FT-IR, Dr. R. K. Chauhan and A. Naidu for AES-
ICP analysis.
I would like to thank my lab members in Light stock processing and reforming group
Mr. Amit Sharma, Dr. Sandeep K. Saxena, Mr. Rajeev Panwar, Dr. Peta
Acknowledgements
Ph. D. Thesis of Mr. Devaki Nandan CSIR-IIP
Sreenivasulu, Mr. Deepak Rohilla, Mr. Tryambakesh Sharma for their kind
cooperation and cheerful atmosphere in the laboratory.
My IIP friends and colleagues Nilesh, Harshal, Subhash, Aamir, Arvind, Rajeev and
Vipin and Sibi are thank full to give me friendly and cooperative atmosphere.
From the beginning of my research work in IIP, I am in contact with various senior
researchers Dr. Bharat Singh Rana, Dr. Bhawan Singh, Dr. Deepak Verma, Dr.
Sanny Verma and Mr. Subodh Kumar they all are helpful to me whenever I need their
help.
During this period I also had the chance to work with various trainees specially
Pankaj Singh, Rakesh thakur are the person whom I have enjoyed my time.
I am deeply indebted to my teachers in school and college Dr. Uma Pathak,
Dr. Sanjay Kumar, Dr. Aashutosh Pandey, Dr. Vipin Joshi; seniors Dr. Kamal
Kumar Bisht, Dr. Girdhar Joshi, Veer Singh Palyal, Girish Pant and Dr. Sanjay
Kumar inspired me and laid foundation for me to pursue higher studies.
Heartfelt thanks to Bhuwan Tiwari, Rajendra Joshi, Veeru, Subhash, Gaurav,
Mannu, Priyanka Tiwari, Manoj Kaloni, Devendra Dhami, Charu, for their
affectionate company and moral support from college study to till date.
During my research work I had an opportunity to work at CSIRO-Earth Science and
Resource Engineering, Clayton Melbourne Australia with Dr. Ken Chiang's group
and interacted with N. Burke, Zim Patel, Jarrod Newnham, Vankat, S. Ali and for
that Department of Science and Technology, India and CSIRO, Australia are
acknowledged to giving me this opportunity
Acknowledgements
Ph. D. Thesis of Mr. Devaki Nandan CSIR-IIP
The words are not sufficient to express my love and gratitude to my parents
for their blessings and moral support. I would like to thank my wife Lalita. Her
support, encouragement, quiet patience and unwavering love were undeniably the
bedrock upon which the past five years of my life have been built. Her tolerance of my
occasional vulgar moods is a testament in itself of her unyielding devotion and love.
I am in dearth of words in expressing my warm feelings of love to my sisters, brother,
sister in law and our daughter Disha.
I also owe a deep sense of thanks to my father-in-law and mother-in-law, brother in
law for their boundless and unconditional support throughout my doctoral study.
I would like to thank the Council of Scientific and Industrial Research (CSIR) New
Delhi, for financial assistance in the form of Research Fellowship during the
course of my research work and CSIR-Indian Institute of Petroleum for
providing me this platform to work on.
Last, but not least, thanks to be my almighty Fatak Shila Baba, whose spirit, gave me
strength and peace during all my life. This thesis would not have been possible unless
Baba’s mercy and love upon me. May my Lord be praised, honored, and loved for all
eternity.
Devaki Nandan
Preface
Ph. D. Thesis of Mr. Devaki Nandan CSIR-IIP
The thesis entitled “Synthesis of porous carbon composites and metal oxides for
catalytic applications” deals with the synthesis and characterization of various novel
porous materials based on carbon, carbon silica composite, carbon embedded metal
nanoparticle and metal oxides and their application have been explored in the field
of catalysis, particularly in the various industrially important organic
transformation reactions such as alkylation of phenol by the direct one-pot liquid
phase reaction, selective hydrogenation in protic environment and glycerol value
addition towards solketal. In this investigation, various acid functionalized carbon
composite, acid functionalized carbon silica composite, hierarchical mesoporous
silica, carbon embedded metal nanoparticle and hierarchical metal oxides have been
synthesized.
The present research work has been carried out in Refining Technology
Division (RTD) CSIR-Indian Institute of Petroleum (IIP), Dehradun-248005,
India, under the supervision of Dr. Nagabhatla Viswanadham. The contents of this
thesis have been presented in seven chapters.
Chapter 1 describes the overview and comprehensive literature survey about porous
carbon composites and metal oxides including their synthesis strategies and catalytic
applications. The chapter concludes the objectives and outlook of the present work.
Chapter 2 comprises the detailed description of different instrumentation and
characterization techniques used to characterize lab synthesized materials. These
Techniques are, Powder X-Ray diffraction (XRD), N2 adsorption-desorption, Fourier
Transform Infrared Spectroscopy (FT-IR), Thermogravimetric Analysis (TGA),
Temperature Programmed Desorption (TPD), Transmission Electron Microscopy
(TEM), Field Emission Scanning Electron Microscopy (FE-SEM), Energy-Dispersive
X-ray Spectroscopy (EDX) and Titration.
Chapter 3 encloses the synthesis, characterization and catalytic activity of sulfonated
nonporous carbon, sulfonated carbon silica composite which has been developed in
laboratory by simultaneous carbonization and sulfonation. The properties of
mesoporous silica material obtained by simple calcination of composite material also
described.
Preface
Ph. D. Thesis of Mr. Devaki Nandan CSIR-IIP
Chapter 4 consists of synthesis, characterization and catalytic activity of various
sulfonated carbon silica composite materials by varying the glucose concentration and
method of synthesis. The properties of mesoporous silica material obtained by simple
calcination of composite material also described.
Chapter 5 describes synthesis, characterization and catalytic activity of magnetically
separable carbon embedded metal-nanoparticles.
Chapter 6 describes the synthesis, characterization of hierarchical ZSM-5 and their
catalytic activity for the tertiary butylation reaction.
Chapter 7 comprises concluding remarks and future prospects of carried out works.
Content
Ph. D. Thesis of Mr. Devaki Nandan CSIR-IIP
Chapter 1 Introduction 1-45
1.1 General Overview to Porous Materials 1
1.2 Foundation and Development of the Field 3
1.2.1 Functionalized porous carbon and carbon composites 3
1.2.2 Zeolites or Porous Metal Oxides 6
1.3 Synthesis Methodologies of Porous Carbon Composites and Metal 10
Oxide Materials Based on Literature Review
1.3.1 Synthesis Methods for Sulfonated Carbon Based Materials 10
1.3.1.1 Sulfonated Non-porous Carbon 10
1.3.1.2 Sulfonated Mesoporous Carbon or Ordered Mesoporous Carbon (OMCs) 12
1.3.1.3 Sulfonic Acid-modified Carbon Nanotubes 13
1.3.1.4 Sulfonic Acid-modified Resins 13
1.3.2 Synthesis Methods for Acid Functionalized Carbon-silica Composite Materials 14
1.3.2.1 Post Oxidation Method 14
1.3.2.2 In-situ Oxidation Method 17
1.3.2.3 Carbonization and Sulfonation Method 18
1.3.3 Synthesis Methods for Porous Carbon Embedded Metal Nano-particles 19
1.3.4 Synthesis Methods for Porous zeolites 20
1.3.4.1 Non-Tempalating Method 20
1.3.4.2 Tempalating Method 21
1.3.4.2.1 Solid Templating 21
1.3.4.2.2 Supramolecular Templating 23
1.3.3.2.3. Indirect Templating 24
1.3.5 Application of Porous Materials in Catalysis 24
1.3.5.1 Acid-Catalysed Reactions 26
1.3.5.2 Base-Catalysed Reactions 27
1.3.5.3 Hydrogenation Reactions 28
Content
Ph. D. Thesis of Mr. Devaki Nandan CSIR-IIP
1.4 Objectives and Outlook of Present work 29
1.5 References 32
Chapter 2 Techniques Used for Characterization of Lab Synthesized
Materials 47-72
2.1 Introduction 47
2.2 Characterization techniques 48
2.2.1 Powder X-Ray Diffraction Analysis 48
2.2.2 Porosimetry 50
2.2.2.1 BET Surface Area 53
2.2.2.2 Pore Volume and Pore Size Distribution Analysis 54
2.2.3 Scanning Electron Microscopy (SEM) 56
2.2.4 Transmission Electron Microscope (TEM) 59
2.2.5 Energy Dispersive X-Ray Spectroscopy 61
2.2.6 Thermo Gravimetric analysis (TGA) 62
2.2.7 Temperature Programmed Desorption (TPD) 63
2.2.8 Fourier Transform Infrared Spectroscopy (FT-IR) 64
2.2.9 Inductively Coupled Plasma -Atomic Emission Spectrometry (ICP-AES) 66
2.2.10. Titration Method 67
2.3 References 67
Chapter 3 Facile synthesis of Sulfonated Nano-porous Carbon,
Sulfonated Carbon-silica-meso Composite and Mesoporous Silica 71-96
3.1 Introduction 71
3.2 Experimental Details 74
3.2.1 Reagents and Chemicals 74
3.2.2 Synthesis of Sulfonated Carbon 74
Content
Ph. D. Thesis of Mr. Devaki Nandan CSIR-IIP
3.2.3 Synthesis of sulfonated Carbon-silica Composite and Mesoporous Silica 74
3.2.4 Catalytic Application of the Synthesized Materials towards Tertiary Butylation
of Phenol 75
3.2.4.1 Liquid Phase Reaction in Round Bottom Flask 76
3.2.4.2 Liquid Phase Reaction in High Pressure Parr Reactor 76
3.3 Results and Discussion 76
3.3.1 Properties of Acid Functionalized Nano Porous Carbon Composite 76
3.3.2 Properties of Acid Functionalized Carbon-silica-meso Composite and
Mesoporous Silica 82
3.3.2.1 Proposed Mechanism for the Formation of SCS and MS 88
3.3.3 Performance of the Catalysts towards Tertiary Butylation of Phenol 89
3.3.3.1 Liquid phase reaction in round bottom flask 89
3.3.3.2 Liquid Phase Reaction in Parr Reactor 90
3.4 Conclusions 93
3.5 References 93
Chapter 4 Optimization of Acid Functionalized Carbon-Silica Composite
Structure for its Catalytic Applications & Mesoporous
Silica Preparation 97-126
4.1 Introduction 97
4.2 Experimental Details 101
4.2.1 Reagents and Chemicals 101
4.2.2 Synthesis of Sulfonated Carbon-silica Meso Composite and Mesoporous
Silica Materials 101
4.2.3 Application of Synthesized Composite Materials for Solketal Synthesis 103
4.3 Results and discussion 104
Content
Ph. D. Thesis of Mr. Devaki Nandan CSIR-IIP
4.3.1 Effect of Synthesis Conditions on Material Properties 104
4.3.2 Porosity and Acidic Properties of the Synthesized Materials 108
4.3.3 Plausible Mechanism for the Formation of SCS, HSCS and HMS Materials 116
4.3.4 Performance of SCS and HSCS Materials towards Solketal Production 119
4.4 Conclusion 122
4.5 References 123
Chapter 5 Synthesis of Carbon Embedded MFe2O4 (M = Ni, Zn and Co)
Nano-particles as Efficient Hydrogenation Catalysts 127-152
5.1 Introduction 127
5.2 Experimental Details 130
5.2.1 Reagents and Chemicals 130
5.2.2. Synthesis of MFe2O4@C Materials 130
5.2.3 Application of Materials for Selective Hydrogenation Reaction 130
5.3 Results and Discussion 132
5.3.1. Scanning Electron Microscopy and Transmission Electron Microscopy
and High Resolution Microscopy 132
5.3.2. X-Ray Diffraction and Porosimetry 134
5.3.3. FT-IR, EDX, CHNS, and ICP-AES Investigation 136
5.3.4 Proposed Mechanism for the Formation of MFe2O4@C Materials 141
5.3.5 Catalytic Performance of Materials for Hydrogenation Reaction 142
5.3.6 Reusability of the Catalyst 146
5.4 Conclusions 148
5.5 References 149
Chapter 6 Synthesis of Hierarchical ZSM-5 Using Glucose as
Templating Precursor and its Catalytic Application 153-170
6.1 Introduction 153
Content
Ph. D. Thesis of Mr. Devaki Nandan CSIR-IIP
6.2 Experimental Details 156
6.2.1 Reagents and Chemicals 156
6.2.2. Synthesis of Hierarchical ZSM-5 Materials 156
6.2.3. Application of Materials for Tertiary Butylation of Phenol 158
6.3 Results and Discussion 158
6.3.1 Crystallinity, Porosity and Acidic Properties of the Synthesized Materials 158
6.3.2. Catalytic Application Materials 165
6.4 Conclusions 167
6.5 References 167
Chapter 7 Concluding Remarks and Future Prospects 171-178
7.1 Facile synthesis of Sulfonated Nano-porous Carbon, Sulfonated
Carbon-silica-meso Composite and Mesoporous Silica 172
7.2 Optimization of Acid Functionalized Carbon-Silica Composite Structure for its
Catalytic Applications & Mesoporous Silica Preparation 172
7.3 Synthesis of Carbon Embedded MFe2O4 (M = Ni, Zn and Co) Nano-particles as
Efficient Hydrogenation Catalysts 173
7.4 Synthesis of Hierarchical ZSM-5 Using Glucose as Templating Precursor and its
Catalytic Application 173
7.5 List of Publications 175
7.6 List of Patents Applied/Filled 177
7.7 Papers Presented/Accepted in Conference, Symposium and Seminar 177
Chapter: 1 Introduction
Chapter 1: Introduction
Porous materials lead accessibility to molecular diffusion
Ph. D. Thesis of Mr. Devaki Nandan CSIR-IIP
Chapter 1. Introduction
Ph. D. Thesis of Mr. Devaki Nandan Page 1 CSIR-IIP
Chapter 1: Introduction
1.1 General Overview to Porous Materials
Porous nano-structured carbon composites based materials and zeolite materials have
attracted considerable interest in the field of catalysis in recent years. Owing to
unique structural, surface and physicochemical properties, porous materials are
widely used in laboratory scale, pilot and industrial scale in diverse research areas,
such as in petrochemicals,1 medicine
2 fine and speciality chemistry,
3 purification,
separation, catalysis, biology, catalyst supports, chemical industry, environment,
energy and advance composites materials.4-16
This subject is a hot topic in recent
years and would be continue to remain so in the coming years. Efficient porous
materials should have high thermal, chemical and mechanical stabilities as well as
appropriate particle size with high surface area and large pore volume.17,18
In
addition, it should have a narrow pore size distribution, which is critical for
size-specific application and a readily tuneable pore size allowing flexibility for
host-guest interaction. One such class of materials, which have been found
great research interest on both academic and industrial levels19
, is the
microporous, mesoporous, and hierarchical materials. According to the
International Union of Pure and applied chemistry (IUPAC)17
classification,
porous materials have been categorized into three categories depending on their pore
size. The porous materials are classified in categories i.e. microporous (pore diameter
<2 nm), mesoporous (pore diameter 2–50 nm) and macroporous (pore diameter >50
nm) materials. Some illustrative examples are depicted in the Figure 1.1 reproduced
from litrature.20
Out of these porous materials, acid functionalized porous carbon-
based composite materials including sulfonated carbon, sulfonated carbon silica
Chapter 1. Introduction
Ph. D. Thesis of Mr. Devaki Nandan Page 2 CSIR-IIP
composites, carbon supported metal nano-particles (showing magnetic properties) and
hierarchical zeolites are playing an increasingly significant role in the development of
alternative clean and sustainable energy technologies.21
Figure 1.1 Examples of micro, meso and macroporous materials, showing pore size
domains and typical pore size distributions
Chapter 1. Introduction
Ph. D. Thesis of Mr. Devaki Nandan Page 3 CSIR-IIP
1.2 Foundation and Development of the Field
1.2.1 Functionalized Porous Carbon and Carbon Composites
From the last 1 decades researchers interest on the development of porous materials
exponentially increasing the first are focusing on the development of porous
materials. Many chemical reactions such as Friedel Crafts alkylation, acetalation,
hydration, esterification, and hydrolysis reactions can be catalyzed by catalysts which
play a vital role in these reactions. Many of these reactions are still carried out by
using conventional liquid acid catalysts like H2SO4. These liquid acid catalysts create
many avoidable problems, such as high toxicity, corrosion, generation of solid
wastes, and difficulty in separation and recovery. The generation of acidity in solid
acid can solve these problems have a number of advantages over the liquid ones, such
as less corrosion, no or less waste, and easy separation and recovery from the reaction
medium. As a result, there has been a great deal of research interest in searching for
environmentally friendly solid acid catalysts to replace environmentally unfriendly
liquid acid catalysts. Over the past decade, various solids with sulfonic acid groups (-
SO3H) have been reported.22-24
The reported structure of the materials are shown in
Figure 1.2. The -SO3H groups can be introduced on porous silica through two main
approaches. One is the post-oxidation method and other is in-situ oxidation method.22-
26 In post-oxidation method the supported thiol groups, which were introduced
through grafting or co-condensation method, were oxidized by post synthetical
technique. However, the porous structure cannot be maintained well after the
postoxidation.23
To solve this drawback, another method named in-situ oxidation
method was subsequently developed.23
In an in-situ oxidation method the silica
precursor, organosulfonic precursor, and oxidant were added together into the
Chapter 1. Introduction
Ph. D. Thesis of Mr. Devaki Nandan Page 4 CSIR-IIP
synthesis process and the oxidation of thiol groups can occur with the preparation.
Sulfonic acid functionalized porous silicas with uniform pores, high surface area and
good stability have been found to exhibit excellent catalytic activities in many
reactions, such as esterification26
condensation and addition reactions27
and alcohol
coupling to ethers.28
To tune the acidic strength of sulfonic acid solids, arene-sulfonic
acid groups were introduced on mesoporous silica materials.29
Figure 1.2 Reported structure of various types of acid functionalized materials in
literature
Organosulfonic-modified periodic mesoporous organosilicas (PMO) have
been shown to display a great catalytic performance. Organosulfonic-modified PMO
catalyst was first used in the alkylation of phenol with 2-propanol.30
Subsequently,
PMO catalysts were tested in many kinds of chemical reactions, such as
esterification31
and condensation.32
Carbon-based materials have always attracted
Chapter 1. Introduction
Ph. D. Thesis of Mr. Devaki Nandan Page 5 CSIR-IIP
much attention in heterogeneous catalysis due to its virtues such as easy modification,
high surface area, high pore volume and their low cost. By introducing -SO3H groups
on carbon, Hara and coworkers21a
discovered a carbon-based solid sulfonic acid
catalyst, which displayed a very high catalytic activity. However, these carbon
materials possess a low surface area, which is not favourable for some catalytic
reactions. The second field of interest for the development of efficient carbon
supported catalyst is to create magnetic properties on the catalyst material as shown
in Figure 1.3. The carbon supported metal nano-particle in its oxide form can be used
as a catalyst to solve the separation problem of small nano-particle. The porous
carbon supported metal nano-particle not only gives the stability to the metal nano
particle but also give higher surface area to the material.
Figure 1.3 Photograph showing magnetic separation of NiFe2O4 nano-particle @C.
Chapter 1. Introduction
Ph. D. Thesis of Mr. Devaki Nandan Page 6 CSIR-IIP
1.2.2 Zeolites or Porous Metal Oxides
Zeolites are a unique class of crystalline aluminosilicates exhibits systematic ring of
pores. The particular properties of zeolites have fascinated scientists from different
backgrounds for over 250 years. They were discovered by mineralogist Axel
Cronstedt in 1756, who noticed an unusually pronounced steam formation upon
heating the mineral stilbite in a blow pipe.33
Accordingly, he coined the material
‘zeolite’, originating from classic Greek, where ‘zeo’ means ‘to boil’ and ‘lithos’
means ‘stone’. It was about 200 years later that, in the 1940s and 1950s, the
pioneering contributions by Barrer, Breck, and Milton on zeolite synthesis enabled to
establish the tremendous potential of zeolites. As a result, in 1954 Union Carbide
commercialized synthetic zeolites as new class of industrial materials for separation
and purification. Few years later, synthetic zeolites were marketed as isomerisation
and cracking catalysts (Mobil Oil). Now a day, zeolites are used in roughly 70
industrial catalyzed reactions in oil refining, petrochemical, and fine chemical
industries.34,35
Out of millions of theoretically possible frameworks36
due to the
connectivity of the zeolite SiO4 or AlO4 tetrahedra over 200 have been synthesized
experimentally.37
A particular framework topology can be ascribed to various zeolites
based on differences in composition (mostly Si/Al ratio) or crystal morphology.
These differences usually originate from zeolite synthesis by variation of gel
composition, crystallization time and temperature, or template used. To date, ~1000
different zeolitic materials have been included in the Atlas of Zeolite Structure
Types.37
This relatively low number related to the meta-stability of zeolites, due to
the majority of the hypothetical structures which are unstable.36
Moreover, of the
synthesized structures, many are not truly zeolites or molecular sieve materials, since
they are not stable upon template removal. Zeolites are typically classified by
Chapter 1. Introduction
Ph. D. Thesis of Mr. Devaki Nandan Page 7 CSIR-IIP
Figure 1.4 Structures and dimensions of different types of zeolite.38
their pore size and composition. Table 1.1 summarizes the most common commercial
zeolites. The size of the pores is typically expressed as the number of Si or Al atoms
on the smallest possible cross-section, e.g. 8, 10, or 12 member rings (Figure 1.4).
Alternatively, they can be categorized by their Si/Al ratio, forming four classes: high,
intermediate, and low Si/Al ratio zeolites and only silica zeolites. The exceptional
performance of zeolites catalyzed reactions due to their strong acidity and uniformly-
sized micropores. These assets enable to catalyze a wide variety of chemical
conversions, while yielding very narrow product distributions. The other concept for
the zeolites is ‘shape selectivity’ (zeolite micropores directing the conversion of a
reagent into a specific product).39
Various types of shape selectivity are distinguished,
depending on whether the pore size limits the entrance of the reacting molecule, the
departure of the product molecule, or the formation of certain transition states as
shown in figure 1.5. These exceptional catalytic features, combined with the ability
to tune both acidity and micropore size, has made the tremendous role of zeolites in
Chapter 1. Introduction
Ph. D. Thesis of Mr. Devaki Nandan Page 8 CSIR-IIP
catalysis. Therefore, based on size exclusion, zeolites can be used to separate
relatively large molecules from smaller ones. In addition to this advantage,
substitution of tetravalent Silicon by trivalent Aluminium in the framework gives rise
to a net negative charge, which is compensated by cations, e.g. H+, Cs
+. These
cations, located in the micropores, are readily exchangeable, making zeolites
prolificion exchangers, for example in detergents. Moreover, if these cationic sites are
exchanged to H+, strong Brønsted acid sites are formed, enabling the application of
zeolites in catalysis. Despite the obvious success of zeolites as solid catalysts, their
potential is only partially exploited due to diffusion and access limitations. The
Table. 1. Pore size and ring size of some known zeolites
Zeolite Framework type Ring member (pore size) Pore size Å
High Si/Al ratio (10-100)
ZSM-5 MFI 10 5.5X5.1
10 5.6X5.3
ZSM-22 TON 10 4.6X5.7
ZSM-12 MTW 12 6.0X5.6
MCM-22 MWW 10 5.5X4.0
10 5.1X4.1
Beta BEA 12 6.7X6.6
12 5.6 X 5.6
Ferrierite FEA 10 5.4 X 4.2
8 4.8 X 3.5
Intermediate Si/Al ratio (2-5)
Clinoptilolite HEU 10 7.5 X 3.1
8 4.6 X 3.6
8 4.7 X 2.8
Mordeniteb MOR 12 7.0 X 6.5
8 5.7 X 2.6
Erionite ERI 8 5.1 X 3.6
Chabazite CHA 8 3.8 X 3.8
Y FAU 12 7.4 X 7.4
L LTA 12 7.1 X 7.1
Low Si/Al (1-1.5)
A LTA 8 4.1 X 4.1
X FAU 12 7.4 X 7.4
Only silica
Silicalite-1 MFI 10 5.5 X 5.1
10 5.6 X 5.3
Chapter 1. Introduction
Ph. D. Thesis of Mr. Devaki Nandan Page 9 CSIR-IIP
Figure 1.5 Types of shape selectivity operate in zeolite
limited size of the micropores with respect to the size of the molecules enforces an
intra-crystalline ‘single file’, or ‘configurational’, diffusion.40
As a result, only the
part of the micropores close the external surface is used in most catalyzed reactions.
Since the external surface area of zeolite crystals is only a fraction (5%) of the total
surface area, an under utilization of the zeolite volume is consequently unimplied.41
As a response to the limited utilization of the active volume in conventional zeolites,
Chapter 1. Introduction
Ph. D. Thesis of Mr. Devaki Nandan Page 10 CSIR-IIP
for over a decade, now an intense and persistent scientific attention focused on
increasing the accessibility of the zeolites active sites by widening of the micropore
channels,41
reducing the transport issues by coupling the intrinsic microporosity with
an auxiliary mesopore network of inter- or intracrystalline nature,42,43
In the latter
case, each porosity level fulfils a distinct complementary task 1) the micropores hold
catalytically active sites, 2) whose access is facilitated by the newly introduced
mesoporosity.41
A large array of lab-scale approaches to synthesize hierarchical
zeolites has been realized.44-53
Bottom-up routes include the modification of the
synthesis protocol resulting in nanosized zeolite crystals46
or zeolites including a
secondary mesopore template.47,50
Top-down routes comprise post-synthetic
treatments of previously grown zeolites by demetallation. Examples here of comprise
steam51
, acid54
or base48
treatments. The more refined approaches that include
swelling agents,52,53
irradiation,55,56
and/or strong oxidizing reagents.56
Although most
of the above-mentioned routes are successful in acquiring mesoporosity and improved
performance in catalyzed reactions. However the majority of bottom-up methods are
not easily amended to industrialization since they involve substantial amounts of
costly and unavailable templates or lead to crystals that are not easily separated from
the mother liquor. Futrher research is going on to achieve hierarchical mesoporous
zeolite for better material having vivid applications.
1.3 Synthesis Methodologies of Porous Carbon Composites and Metal
Oxide Materials Based on Literature Review
1.3.1 Synthesis Methods for Sulfonated Carbon Based Materials
1.3.1.1 Sulfonated Non-porous Carbon
Chapter 1. Introduction
Ph. D. Thesis of Mr. Devaki Nandan Page 11 CSIR-IIP
Hara et al.57
first time reported a new kind of carbon moiety having -SO3H protonic
acid group by incomplete carbonization of hydrocarbons (naphthalene) by
sulfonation. The sulfonation reaction was carried out under high reaction temperature
(200-300 ºC). However, this new kind of carbon-based sulfonic acid catalyst having
the leached out problem during liquid phase reactions above 100 ºC and its catalytic
activity is heavy limited for bulky molecular transformations (long chain fatty acids).
Later on Toda et al.21a
follow the two step method for the preparation of material
(scheme 1.1). They have employed sucrose, starch or cellulose as the carbon
precursor for low temperature carbonization process (400 ºC) to producs small
polycyclic aromatic carbon sheets in first step followed by sulfonation by sulfuric
acid (concentrated or fuming) in second step. Amorphous carbon prepared by this
method enhanced the stability of resultant carbon sulfonic acid catalysts greatly. The
effect of the carbonization temperature was also investigated by Okamura et al.58,59
The authors found that the active centres for the carbon carbonized at 550 ºC are not
fully available for reactants. Because with increasing carbonization temperature,
carbon materials become dense and the fewer sites for sulfonation remain for
sulfonation (sulfonation at surface is only possible). Sulfonated amorphous carbon
Scheme 1.1 Synthesis procedure for preparation of sugar based catalyst21a
Chapter 1. Introduction
Ph. D. Thesis of Mr. Devaki Nandan Page 12 CSIR-IIP
prepared under lower temperature shows better catalytic performance because of high
phenolic -OH and -COOH in addition to -SO3H groups on the catalyst.
1.3.1.2 Sulfonated Mesoporous Carbon or Ordered Mesoporous Carbon
(OMCs)
These catalyst supports possessing high surface, narrow pore size distribution, large
pore volume, high densities of functional groups and good accessibility to active sites
facilitate the bulky molecular reactions. Lee et al., 60
Ryoo et al., 61
combindely
discovered the OMCs consisting of three-dimensional regular arrays of uniform
mesopores where they have employed ordered mesoporous silica MCM-48 as the
template. This process includes three steps of sythesis 1) polymerization of carbon
source in the pores of the templates, 2) carbonization at high temperature under
nitrogen atmospheres and 3) subsequent removal of the templates. There after various
researchers employed different mesoporous silica as a template to prepare various
OMCs62
. Wang et al.63
functionalized OMCs by covalent attachment of sulfonic acid-
containing aryl radicals. Wang et al.64
Compared CMK-5 with CMK-5-SO3H which
can be viewed as a material with a hydrophobic substrate and hydrophilic functional
groups. Such amphiphilic properties would allow CMK-5-SO3H to be an efficient
solid catalyst in both hydrophobic and hydrophilic environments. The CMK-5-SO3H
exhibits high activity for esterification reaction of acetic acid with methanol and good
recyclability, due to strong attachment of aryl sulfonic acid group on the substrate
through the stable C-C bond. CMK-5-SO3H also shows high catalytic activity for the
production of biodiesel involving long chain molecular structure because of larger
pores and higher surface area. Introducing the -SO3H groups onto OMCs can also be
Chapter 1. Introduction
Ph. D. Thesis of Mr. Devaki Nandan Page 13 CSIR-IIP
allowed through sulfonation reaction using concentrated sulphuric acid (98%) under
high temperature (150 ºC to obtain the carbon based sulfonic acid catalysts.64
1.3.1.3 Sulfonic Acid-modified Carbon Nano-tubes
The CNT was first sulfonated by Peng and co-worker 65
using concentrated sulphuric
acid under high temperature (250 ºC). The resultant sulfonated CNT exhibiting high
acid density and thermal stability was observed to be suitable for high catalytic
activity through the esterification reaction of methanol with acetic acid. Later on Yu
et al.,66
have chosen Single-walled carbon nano-tubes (SWCNTs) as the support for
the high temperature sulfonation reaction. The high catalytic activity for sulfonated
SWCNTs can be explained by the strong acidity of sulfonic group and the ability of
SWCNTs to support functional groups.
1.3.1.4 Sulfonic Acid-modified Resins
Amberlyst is a polymer based catalysts having the sulfonic acid type groups. These
types of catalysts are adding advantage to catalysis as have both economic and
environmental drivers to improve organic transformations. Hart and co-workers67
prepared series of macroporous sulfonated poly(styrene-co-divinylbenzene) ion-
exchange resins with varying levels of sulfonation. They have used the catalyst for
the dehydration of 1-hexanol under flow conditions and for the hydration of propene.
These persulfonated resins, which were sulfonated at levels above one sulfonic acid
group per aromatic ring, also showed higher thermal stabilities than conventional
resins, which were sulfonated at just below one acid group per aromatic ring. Both the
increase in acid concentration in the internal solution and in the level of di-
sulfonation contributes to an increase in acid strength.
Chapter 1. Introduction
Ph. D. Thesis of Mr. Devaki Nandan Page 14 CSIR-IIP
1.3.2 Synthesis Methods for Acid Functionalized Carbon-silica Composite
Materials
There are several methods reported for the synthesis of carbon silica composite
materials among these the following three methods are widely used given in scheme
1.2.
Scheme 1.2 Common synthetic methodologies employed for acid functionalized
carbon-silica composite materials in literature.
1.3.2.1 Post Oxidation Method
The introduced thiol groups could be oxidized into sulfonic acid groups by using
large excess of oxidant such as hydrogen peroxide as shown in scheme 1.3. Post
oxidative synthesis method for the preparation of silica based sulfonic acid catalysts
based on the covalent attachment of Periodic mesoporous organosilicas (PMO)
composed of hybrid inorganic-organic frameworks with ordered mesopores were first
Chapter 1. Introduction
Ph. D. Thesis of Mr. Devaki Nandan Page 15 CSIR-IIP
synthesized in the late 1990s (Inagaki et al.,68
Melde et al.,69
). The synthesis strategy
of PMO is based on the condensation of organosilanes such as in the presence of the
corresponding surfactant, in which the organic moiety is covalently attached to two
trialkoxysilyl groups. PMO exhibited a homogeneous distribution of organic
fragments and inorganic oxide within the framework accompanied by highly ordered
structures and uniform pore size distributions, which is highly desired in the
applications of catalysis. The combination of acidic groups and hydrophobic
framework may result in interesting surface properties enhancing diffusion of
reactants and products in acid-catalyzed reactions. Inagaki et al.68
reported the
synthesis of PMO with crystal-like pore walls having a surface structure with
alternating hydrophilic and hydrophobic layers, composed of silica and benzene with
a periodicity of 7.6 Å. Through the direct sulfonation reaction using fumed sulfuric
Scheme 1.3 Synthesis scheme for -SO3H functionalized carbon-silica composite
materials by post oxidative method.
acid, -SO3H groups were attached onto the pheneylene group located within
hydrophobic benzene layers. Yang et al.,70
symthesized a material by co-condensation
of 1,4-bis(triethoxysilyl)benzene and 3- mercaptopropyltrimethoxysilane using a
surfactant template in basic conditions the thiol-functionalized benzene-silicas
possessing mercaptopropyl (-C3H6SH) groups which upon postoxidation gave novel -
Chapter 1. Introduction
Ph. D. Thesis of Mr. Devaki Nandan Page 16 CSIR-IIP
SO3H functionalized mesoporous benzene-silica materials. Kapoor et al.71
also
reported the synthesis of bi-phenylene bridged bi-functional hybrid mesoporous
materials functionalized with sulfonic-acid functionalities by co-condensation of 4,4-
bis- (triethoxysilyl)biphenyl precursor and 3-mercaptopropyltrimethoxysilane in a
basic medium and cationic surfactant followed by an oxidation treatment. The authors
claimed that due to the equimolar ratio of phenylene to silica, which provides the
possibility to exert an enhanced hydrophobic character in the resulted PMO material.
The attachment of alkyl sulfonic acid groups to the surface of MCM and HMS type
materials were also done. Van Rhijn et al., first functionalized calcined MCM and
HMS samples with propane-thiol groups by reaction of the surface silanols with 3-
mercaptopropyltrimethoxysilane (MPTMS)72
. Both grafting and direct reaction
methods were adopted in this work. In grafting processes the surface concentration of
organic groups is constrained by the number of reactive surface silanol groups present
and by diffusion limitations. These restrictions may be overcome by direct synthesis
reported by Van Rhijn et al.,73
in which they employed MPTMS and TEOS
(Si(OEt)4), which were hydrolyzed together in the presence of an ionic or a non-ionic
surfactant (viz. C16NMe3Br and nC12-amine), leading to MCM or HMS type
materials, respectively. Following these pioneering works, the post oxidative
synthesis strategy has been expanded to the use of other different surfactants and
synthesis conditions. Thiol containing mesoporous silica material was also
synthesized by Margolese et al.,23
adopting co-condensation of TEOS, MPTMS and
employing a triblock copolymer (poly(ethyleneoxide)-poly-(propyleneoxide)-
poly(ethyleneoxide), Pluronic 123, EO20-PO70EO20) as template under acidic
conditions. Organosulfonic-modified porous silica materials prepared in
postoxidation method have yielded the material with lower scattering intensities in
Chapter 1. Introduction
Ph. D. Thesis of Mr. Devaki Nandan Page 17 CSIR-IIP
XRD that indicated relatively poor long-range ordering in comparison to the starting
material containing the thiol groups22
, following a decrease in the surface area and
pore volume after oxidation of thiol groups incorporated and reduces the potential
application of these catalysts.24
The post oxidation method not only needs a large
excess of oxidant used in the process but also does not allow quantitative reaction of
thiol groups, and in some cases, leaching of sulphur species is clearly evidenced. The
presence of un-oxidized sulphur species might have a negative effect on the catalytic
performance of these materials.
1.3.2.2 In-situ Oxidation Method
Margolese et al.,23
used the in-situ oxidation method to create periodic ordered
propylsulfonic-modified mesoporous silica with pore sizes up to 70 Å through
cocondensation of TEOS and MPTMS, which employed Pluronic 123
(EO20/PO70/EO20) as the templating surfactant in acid medium.23
The in-situ
oxidation method as shown in scheme 1.4 profoundly influences the physical and
chemical properties of the propylsulfonic-modified mesoporous material relative
Scheme 1.4 Synthesis scheme for -SO3H functionalized carbon-silica composite
materials by in-situ oxidation method.
Chapter 1. Introduction
Ph. D. Thesis of Mr. Devaki Nandan Page 18 CSIR-IIP
to that made by post oxidation technique. The in-situ oxidation method produces
SBA-15 modified materials with greater oxidation efficiency (100% vs 25-77%), with
larger more uniform pores, higher surface areas and good long-range order in contrast
to post oxidative method. The resultant sulfonic mesoporous silica with acid
capacities several times greater than those achieved with post oxidative method and
with thermal stabilities to 450 ºC in air. Van Grieken et al.74
employed non ionic
surfactants other than Pluronic 123 (EO20/PO70/EO20), through the in-situ oxidation
procedure to prepare propyl sulfonic modified hexagonally meso-structured materials.
They tailored the pore size of these sulfonic mesoporous materials from 30Å to 110Å
conveniently modifying the synthesis conditions using Pluronic 123 as template and
acid conditions. Popylsulfonic-modified SBA-15 synthesized through the in-situ
oxidation demonstrated significant activity toward biodiesel production under
relatively mild conditions with refined and crude vegetable oils as feedstock.74
The
large surface area and pore diameter of the mesoporous support as well as the
moderate acid strength of acid sites are helpful for the remarkable catalytic
performance, which are necessary to improve internal diffusion of bulky oil species
and to minimize possible deactivation of catalytic sites by strong adsorption of polar
by products such as water and glycerol.
1.3.2.3 Carbonisation and Sulfonation Method
The third method involves two step process of carbonization of the silica-carbon
composite material followed by its sulfonation as shown in Scheme 1.5.75-78
S. V.
Vyver, et al.75
synthesized the silica carbon composite by applying a method in which
they used sucrose as carbon precursor, Pluronic F127 triblock copolymer
(EO106PO70EO106, Mw = 12600) F127 as structure-directing amphiphilic
Chapter 1. Introduction
Ph. D. Thesis of Mr. Devaki Nandan Page 19 CSIR-IIP
surfactant and tetra-ethyl orthosilicate (TEOS) as a silica source. In first step they
take F127 ethanol then added HCl to form a clear solution followed by addition of
TEOS and sucrose. The mixture was then left for 20 h at 40 ºC to evaporate ethanol
and for 24 h at 150 ºC to thermo polymerise. The obtained material then carbonised at
different temperature under nitrogen for 15 h. In second step the obtained material
was treated with concentrated sulphuric acid at 140 ºC for 15 h in Teflon-lined
autoclave and got sulfonated silica/carbon nano-composites. Later on Gupta et al.76
prepared a similar type of material by using natural organic compounds (glucose,
maltose, cellulose, chitosan and starch) and silica. In their synthetic procedure they
partially carbonise the precursors followed by its sulfonation to synthesize the final
material.
Scheme 1.5 Synthesis scheme for -SO3H functionalized carbon-silica composite
materials by carbonization and sulfonation method.
1.3.3 Synthesis Methods for Porous Carbon Embedded Metal Nano-
particles
According to the research findings on the synthesis steps of carbon based materials,
the carbon source first polymerizes to form small spheres or agglomerated particles
which begin to carbonize to form multi-aromatic carbon sheets that eventually lead to
the formation of a well condensed inner dense carbon matrix with an outer layer of a
Chapter 1. Introduction
Ph. D. Thesis of Mr. Devaki Nandan Page 20 CSIR-IIP
multi aromatic ring during the process of hydrothermal synthesis and heat
treatments.79-83
The high temperature carbonization treatments applied during the
process give the material thermal and chemical stabilities to efficiently protect the
metal spheres from being dissolved in a protic environment. Moreover, the outer
multi-carbon layer of the material can have many functional groups, such as
carboxylic, aldehyde and hydroxyl groups on their surface, suitable for establishing a
chemical interaction with the desired compounds such as noble metal nanoparticles
(NPs) to obtain metal functionalized catalysts.84,85
Based on the above advantages,
many researchers have tried to attach metal spheres or metal nanoparticles onto the
carbon support.86–88
Wang et al.,89
used oleic-acid-decorated Fe3O4 NPs as the core of
Fe3O4/ carbon spheres. Zhang et al.90
reported the fabrication of functional 1D
magnetic NP chains with thin carbon coatings using urea as the surfactant.
1.3.4 Synthesis Methods for Zeolites (Porous Crystalline Aluminosilicate)
1.3.4.1 Non-Tempalating Method
This method is widely used in industry to introduce hierarchical porosity to the
material. It involves post synthesis demetalation of the material. In dematalation of
the material is carried out through various approaches such as steam treatment34
, acid
leaching37
, and desilication31
. The most well studied demetalation methods for
introducing intracrystalline pores in zeolites are dealumination and desilication.
Dealumination involves preferential extraction of framework aluminium by acid
leaching using nitric or hydrochloric acid solutions at temperatures ranging from
323 to 373ºC, or by steam treatment at relatively high temperatures between 500–
600°C. However, the resultant meso-structured zeolites obtained from
dealumination contain less crystallinity compared to its parent zeolite materials.
Chapter 1. Introduction
Ph. D. Thesis of Mr. Devaki Nandan Page 21 CSIR-IIP
On the other hand, desilication, the preferential extraction of Si from the zeolite
framework by treatment in aqueous alkaline solution has proven to be more effective
way for creating meso-porosity in the zeolites crystals compared to the dealumination
method.
1.3.4.2 Templating Method
Templating method is one of the most widely used methods for the synthesis
of hierarchical structured zeolite materials with different morphologies and
characteristics. Generally, it is categorized into three categories: solid templating,
supramolecular templating, and indirect templating. In solid and supramolecular
templating, the zeolites crystal is in intimate contact with either a solid material or a
supramolecular assembly of used surfactant molecules that are subsequently removed
to generate the meso-porosity. Depending on method of synthesis various type of
porous structure can be prepared (Table 1.2)
1.3.4.2.1 Solid Templating
A large variety of solid templates (such as polymers, resins, carbon, organic aerogels,
materials with different structures, inorganic compounds, and biological templates
etc.) have been used for the synthesis of hierarchical mesoporous zeolites
materials with different morphology and characteristics. 91-95
In spite of these
different variety of solid templates, the use of different types of porous carbon
as a solid templates seems to be the most effective and versatile approach.
Porous carbon can be used to produce nano-meter sized supported zeolite crystals and
hierarchically arranged zeolites crystals. Jacobsen et al.91
reported the first example of
the creation of meso-structured zeolites by a solid templating method. They
Chapter 1. Introduction
Ph. D. Thesis of Mr. Devaki Nandan Page 22 CSIR-IIP
have used nano carbon particles, pre-treated with acidic/alkaline solution as
mesoporous templates. These nano carbon particles were encapsulated by growing
Table 1.2 Hierarchy in zeolitic crystals-some examples classified with respect to their
synthesis methods
Method
Type of template Type of zeolite Type of porosity Reference
1. Templating
A. Solid
templating
Carbon blacks,
carbon
nanofibers,
carbon
nanotubes
MFI,Si-1,
ZMM-12
Micro/Meso/Macr 91
colloidal silica,
carbon
mesoporous,
molecular sieves
MFI,
Mesoporous
aluminosilicate
molecular
sieves
Micro/Meso 92
Aerogels,
polymer, resin,
BEA, MFI, Y Micro/Meso 93
Inorganic
compound
Silicate-1 Micro/Meso 94
Organosilane MFI,LTA,TS-1 Micro/Meso 95
B. Supramolecular
templating
Microemulsion,
reverse micelles
Silicalite-1 96
Surfactant
mediated oating
of zeolite
MCM-
41/FAU,
MOR/MCM-
41, MCM-
41/BEA
Micro/Meso 97
Delamination ITQ-2, ITQ-6,
MFI
Micro/Meso 98
C. Indirect
Templating
Crystallization
of zeolites seed
on mesoporous
materials
MFI, Y Micro/Meso 99
2 Non-Templating (Demetalation)
Dealumination MOR, MFI,
FER
Micro/Meso 100
Desilication MFI, BEA,
ZSM-12,
MOR, FER,
MCM-22,
ITQ-4,
Silicalite-1
Micro/Meso 101
Chapter 1. Introduction
Ph. D. Thesis of Mr. Devaki Nandan Page 23 CSIR-IIP
zeolites crystals during synthesis, resulting in zeolites crystals embedded with carbon
after zeolites crystallization. Removal of the embedded carbon matrix after synthesis,
results in ZSM-5 zeolite crystals with case like meso-porosity. However, for the
processing of bulky molecules, the cave-like meso-porosity in the ZSM-5 zeolite
creates accessibility and mass transfer problems. To overcome this problem, meso-
structured long carbon nano-tube or nano-fiber templates have been used for the
synthesis of zeolites crystals with uniform and straight mesoporous channels of
diameter from 12-30 nm. Recently, a novel and facile method has been employed to
synthesize zeolites with mesopores using meso-structured carbon nano-tubes as
templates.91
1.3.4.2.2 Supramolecular Templating
In this method, an organized assembly of surfactant molecules is used as the
template for creating intercrystalline or intracrystalline meso-porosity within
zeolites. In all successful synthesis of mesoporous zeolites by using the
supramolecular templating method, the silica based species in the synthesis of
zeolites were in direct contact with the supramolecular template during the
crystallization process.96-98
Due to the presence of various factors (e.g. interaction
with silica-based species, stability, and morphology) during the zeolite
crystallization process, the selection of appropriate supramolecular template is of
vital importance in creating the mesoporous structure. Using soft-templates that
have strong interactions with silica-based species has the more chance of fabricating
mesoporous zeolites. Over the past few years, numerous successful examples of the
use of soft-templates to create mesoporous zeolites have been reported.,96-98
Ryoo
et al.95a
first time developed a direct synthesis route to mesoporous MFI
Chapter 1. Introduction
Ph. D. Thesis of Mr. Devaki Nandan Page 24 CSIR-IIP
zeolites with easily tunable, uniform mesopores using amphiphilic organosilanes
([(CH3O)3SiC3H6N(CH3)2CnH2n+1]Cl), as supramolecular template.
1.3.4.2.3. Indirect Templating
Indirect templating method deals with the formation of hierarchical material in the
absence of a distinct mesopores or micropores template. In this method materials are
formed either from material or by controlled deposition of zeolites crystals onto
a mesoporous supporting material.99
In both strategies, the overall morphology of
the hierarchical mesoporous zeolites material is more or less retained during the
zeolites crystallization or deposition step. There are only a few different preparative
approaches belonging to this category, the majority of which related to partial zeolite
crystallization in ordered mesoporous materials. Using this methodology, zeolites
materials with hierarchical porosity can be produced by crystallization of mesoporous
materials such as SBA-15 in the presence of appropriate molecular zeolite structure
directing agents. This method include the following two steps: (i) assembly of an
mesoporous phase by templating; (ii) partial crystallization of the mesophase to
a zeolites phase.
1.3.5 Application of Porous Materials in catalysis
The fascinating characteristics of porous materials have made these materials
highly desirable candidate for many applications, particularly in catalytic
application as catalysts and catalyst supports. The development of different
class of porous materials like porous carbon, porous composites, porous
magnetically separable carbon composites, porous mesoporous zeolites and
hierarchical mesoporous zeolites has led to a revolution in the field of
Chapter 1. Introduction
Ph. D. Thesis of Mr. Devaki Nandan Page 25 CSIR-IIP
heterogeneous catalysis. These materials have been extensively used in various
catalytic applications depending upon their unique properties. Zeolites and related
microporous molecular sieves have been implemented successfully in various
industrial applications such as petroleum refining, petro chemistry, and fine
chemical synthesis, due to their remarkable stability (mechanical, hydrothermal,
thermal and chemical), acidic nature, and high catalytic activity. However, despite
these distinguished properties, the different pore window sizes of zeolites ranging
from 5 Å to 12 Å cause a mass transfer problem in processing of large molecules
and viscous fluids. Other drawback of these zeolites is that they are not stable in
aqueous environment. Therefore, to meet these demands, numerous synthetic
strategies to create zeo-type materials with pore diameter larger than those of
the traditional zeolites and porous carbon composite having acidity were developed.
These porous materials with pore diameter in the range of mesopores provide
improved diffusion and accessibility for larger molecules and viscous fluids. Owing
to the extremely high surface area and large pore size, ordered porous materials
can be employed as effective heterogeneous catalysts for performing several
catalytic reactions. Ordered porous materials have frequently been used as supports
for catalysts rather than as catalysts as such. Acidic and redox functionalities were
generated in the materials by the incorporation of active sites in the silica walls or by
the encapsulation of well-defined homogeneous complexes inside the pores. Hence,
the catalytic activities of all the porous materials are basically dependent on the acid,
base and redox properties of the materials, which have been summarized in the
subsequent section.
Chapter 1. Introduction
Ph. D. Thesis of Mr. Devaki Nandan Page 26 CSIR-IIP
1.3.5.1 Acid Catalysed Reactions
Propylsulfonic-modified FSM-16 mesoporous silica was investigated in the
acetalization of carbonyl compounds with ethylene glycol, which showed a higher
rate and 1,3-dioxolane yield than conventional heterogeneous solid acids such as
zeolites, montmorillonite K10 clay, silica-alumina, and the sulfonic resin (Amberlyst-
15)27b
. Propylsulfonic-modified FSM exhibits stable recycle catalytic activity with no
leaching of sulfonic acid groups. Inorganic solid acid materials have been found
to be a strong candidates in various acid catalyzed chemical reactions such as
etherification,102
esterification,103
alkylation,104
Acetalation,105
cracking,106
,
dehydration,107
oligomerization,108
isomerization109
etc. These inorganic solid acid
materials provide an environmentally friendly alternative replacement of
corrosive liquid acid catalysts such as H2SO4, HF, and H3PO4 for acid–
catalyzed processes. In the last two decades, mesoporous zeolites and porous
carbon composite materials have attracted a great attention as solid acid catalysts and
used in various industrial processes and fine chemical synthesis. One of the most
important examples is the catalytic alkylation of aromatic hydrocarbons carried
out in the presence of various mesoporous materials. J. Shinae et al.104j
reported
the alkylation of benzene using benzyl alcohol as alkylating agent over Al-
MCM-41 solid acid catalyst. The selective formation of cumene as the main product
in the isopropylation of benzene by isopropanol was reported by Valtierraet al.104k
Further, the large pore of MCM-41 combined with acidity on the walls was
specially conceived to carry out catalytic cracking of large molecules. The acidity
of mesoporous materials like Al-MCM-41 is much weaker than that of
microporous zeolites. In order to overcome this drawback, hybrid inorganic organic
mesoporous materials with alkyl sulfonic acid groups have been synthesized and
Chapter 1. Introduction
Ph. D. Thesis of Mr. Devaki Nandan Page 27 CSIR-IIP
studied for their applicability in various reactions.110
Das et al.,111
reported that
mesoporous MCM-41 and MCM-48 silicas anchored with sulfonic acid (–
SO3H) groups via post synthesis modification are very effective for the synthesis
of Bisphenol-A by liquid-phase condensation of phenol with acetone. Exceptionally
high yield of the acetylated products in the acetylation of anisole was observed by
Kwon et al.,112
in the presence of sulfonic acid-modified MCM-41 mesoporous
materials that was prepared using a silane containing tetrasulfide linkages.
Recently, Melero et al.,113
have shown that SBA-15-PrSO3H is a promising and
recyclable catalyst for transesterification of various vegetable oils. More
recently, periodic mesoporous silica (PMO) functionalized materials have been used
in biodiesel production. Karimi et al., 114
reported biodiesel production via direct
transesterification of a variety of vegetable oils in the presence of sulfonic acid based
PMO materials.
1.3.5.2 Base Catalysed Reactions
Porous materials with basic properties have shown considerable potential for a
number of industrially important reaction.115
Ion-exchanged or ion impregnated
microporous zeolite materials were used as base catalyst from the beginning of the
1990s. However, the low basic strength of the ion-exchanged zeolites, limits
their use in organic synthesis. In order to increase the basicity or base sites, various
alkali salts have been impregnated in to the cavities of zeolites.115
Kloetstra et
al.115b
reported that Cs+ ion exchanged MCM-41 showed high activity in
Knoevenagel condensation reaction as compared to the Na+ ion exchanged MCM-
41 due to the high basicity of the Cs-MCM-41. The catalytic activity of the
alkali metal ion exchanged zeolite materials is strongly dependent on the type of
Chapter 1. Introduction
Ph. D. Thesis of Mr. Devaki Nandan Page 28 CSIR-IIP
alkali cation present, the order being K > Rb > CS > Na > Li. A new synthesis
strategy has been adopted for the development of porous basic catalysts. This
strategy involves high temperature (700-1000 °C) treatment of amorphous
aluminium orthophosphate, zircononium phosphate and vanadophosphates materials
with ammonia. In this strategy oxygen atom is replaced by nitrogen that provides
basic sites. The amorphous oxynitrides are considered to be more strongly basic
catalysts than alkali ion-exchanged zeolites and comparable to hydrotalcites or MgO
base catalyst. Similarly, various organic bases could be bound to the surface of
porous silica materials by using the reaction of silanol groups of silica based
materials with 3-chloropropyltriethoxysilane and different organic base such as
piperidine, pyrrolidine, pyrimidine in subsequent steps. These materials were
reported to be effective base catalysts for various reactions such as Claisen–Schmidt
condensation,116
Knoevenagel condensations117
etc.
1.3.5.3 Hydrogenation Reactions
The selective hydrogenation of organic molecules is one of the most important
chemical reactions for the synthesis of new compounds and the synthesis of effective
catalysts that can catalyze hydrogenation of arenes under milder conditions remains a
significant challenge.118
The reaction can be catalyzed homogeneously or
heterogeneously, but it is well recognized that the heterogeneous version is by far
more interesting from an industrial point of view,119
offering well-known benefits in
terms of waste reduction, easy separation of the catalysts and its recyclability.120
With
the aim of improving efficiencies, new catalysts and supports are being developed
continuously. Transition metals, such as Pd, Pt, Ru, Rh or Ni, both homogenous and
heterogeneous, are catalysts of choice for this reaction. However, in an effort to
Chapter 1. Introduction
Ph. D. Thesis of Mr. Devaki Nandan Page 29 CSIR-IIP
develop a more sustainable approach, their cost, toxicity and potential depletion has
fuelled the development of alternative hydrogenation catalysts. Iron, Cobalt and
Nickel complexes were shown to be active catalysts121
for the hydrogenation of
olefins,122
and the selective hydrogenation of alkynes to alkenes. Recent
developments in nano materials provided efficient methods for catalyst development
and the use of iron in the form of suspendable nano particles for its applications in
catalysis is interesting as it also provides magnetic properties suitable for easy
separation of the catalyst from the reaction mixture. One of the challenging tasks in
this regard is the achieving stability of metal nano particles on the catalyst support.
Stein et.al,123
have overcame this limitation by stabilizing Fe NPs made by
decomposition of Fe(CO)5 onto graphene sheets. Although the resulting particles
were active hydrogenation catalysts, they were prone to oxidation in the presence of
either oxygen or water atmosphere prevail during the reaction.
1.4 Objectives and Outlook of the Present Work
Based on the above discussion, the materials to possess good catalytic activity should
have properties such as porosity with inter connectivity of pores, crystallinity, high
surface area, thermal stability, acid bearing capacity or acid site density and strength
of acid sites. Zeolites, by virtue of most of above mentioned properties, have been
emerged as industrial catalyst in petrochemical refineries, may also extend to specific
application in fine chemicals. However the presence of smaller micropores that
cannot accommodate larger molecules make the application limited and demands
novel synthesized materials for having large dimension porosity such as meso, or
combination of micro-meso and micro-meso-macro (hierarchical pores). To solve
these problems porous carbon composites and metal oxides with infinite network
Chapter 1. Introduction
Ph. D. Thesis of Mr. Devaki Nandan Page 30 CSIR-IIP
materials can be functionalized by acid or metal ions or ion–clusters are emerging as
tremendous scope in chemical and material research field. Thus Precise designing
strategies for acid functionalized porous carbon composite, metal supported nano-
particles and hierarchical zeolitic metal oxides by using low cost carbon source (such
as petroleum waste, glucose, levulinic acid and phloroglucinol) or structure directing
agent are the key factors for development of cost effective synthetic protocols are the
contemporary challenges of this field which need to be addressed.
The present work is focused on the development of new 1) porous carbon
composites, with acidity and magnetic properties 2) hierarchical porous zeolites
having diverse structural features enriching the priori information useful towards the
‘designing’ of novel materials. In view of the importance of porous materials the
present work aimed to develop new porous material which is stable in liquid phase
reactions or gas phase reactions where polar compounds are the side products. These
reactions are alkylation of phenol, glycerol value addition, hydrogenation in protic
environment and bio-oil up gradation. Notable emphasis on the preparation of acid
functionalized porous carbon, magnetically separable carbon composite and
hierarchical metal oxide has been given by applying the following novel concepts.
The simultaneous carbonization and sulfonation of low cost carbon precursors
(coal tar or glucose) has been adopted to synthesize thermally stable acid
functionalized nanoporous carbon, acid functionalized carbon silica composite
material having high acidity, high surface area useful for bulky molecular
transformations. The acid functionalized carbon silica composite also can be
used for the synthesis of mesoporous silica by simple calcination and the
Chapter 1. Introduction
Ph. D. Thesis of Mr. Devaki Nandan Page 31 CSIR-IIP
resultant mesoporous silica has wide application depends on metal
functionalization.
Various acid functionalized carbon silica composite samples has been
synthesized by varying the glucose concentration adopting thermal and
hydrothermal method.
A novel concept of using levulinic acid for the synthesis of carbon
supported metal nano-particle has been adopted having the carboxylic for
interaction with M2+
and Fe 3+ and carbonyl groups for interaction with
phloroglucinol. The levulinic acid also establishes effective metal-support
interaction in which interaction of levulinic acid restricts the agglomeration of
metal nano-particle so that their size remains smaller. The Simultaneous
polymerization then carbonization at higher temperature gives stable carbon
supported nano-particle (no leaching and oxidation in protic solvent viz.
ethanol). The advantage of the present study is that both the chemicals
levulinic acid and phloroglucinol used are cheaper, renewable, non-hazardous
which can avoid use of high cost surfactant for stabilizing
nanoparticles. The synthesized materials have been applied for the selective
side chain hydrogenation reaction.
A novel concept of using low cost glucose as a templating precursor
has been adopted to get hierarchical ZSM-5. In the present study cheaper,
renewable, non-hazardous compound glucose was used as carbon source that
avoids use of high cost surfactant and organosilane. Further , aqueous
ammonia instead of NaOH was used as alkali source during crystallization
for the direct production of protonic zeolite that avoids the otherwise
required additional steps of ion-exchange with ammonia and calcination of
Chapter 1. Introduction
Ph. D. Thesis of Mr. Devaki Nandan Page 32 CSIR-IIP
the final material. The other important advantage of the present method lies in
obtains desired porosity by simple method of varying glucose concentration
for fine tuning the pore size. The materials are applied for bulky molecular
transformation of t-butylation of phenol also an industrially important
reaction.
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110, 11924. (h) K. Bachari, R. M. Guerroudj, M. Lamouchi, Reac. Kinet.
Mech. Cat., 2011, 102, 219. (i) K. Song, J. Guan, S. Wu, Y. Yang, B. Liu and
Q. Kan, Catal. Lett., 2008, 126, 333. (j) J. Shinae, R. Ryoo; J. Catal., 2000.
195, 237. (k) J. M. Valtierra, O. Zaldivar, M. A. Sanchez, J. A. Montoya, J.
Navarrete, J.A. de Los Reyes, Applied Catal. A, 1998, 166, 387.
105. (a) E. García, M. Laca, E. Pérez, Á. Garrido and J. Peinado, Energy Fuels,
2008, 22, 4274. (b) C. X. Da Silva, V. L. Gonҫalves and C. J. Mota, Green
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Chem., 2009, 11, 38. (c) G. Vicente, J. A. Melero, G. Morales, M. Paniagua
and E. Martín, Green Chem., 2010, 12, 899.
106. W. H. Chen, Q. Zhao, H.-P. Lin, Y.-S. Yang, C.-Y. Mou, S. B. Liu,
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107. (a) E. D’Hondt, S. Van de Vyver, B. F. Sels and P. A. Jacobs, Chem.
Commun., 2008, 6011. (b) M. Dasari, P. Kiatsimkul, W. Sutterlin, G. J.
Suppes, Appl. Catal. A, 2005, 281, 225. (c) A. Alhanash, E. F.
Kozhevnikova and I. V. Kozhevnikov, Appl. Catal. A:Gen., 2010, 378, 11.
108. (a) B. Chiche, E. Sauvage, F. Di Renzo, I.I. Ivanova, F. Fajula, J. Mol. Catal.
A: Chem. 1998, 134, 998, 145. (b) X. Hu, M.L. Foo, G. K. Chuah, S.
Jaenicke, J. Catal., 2000, 195, 412.
109. D. Farrusseng, K. Schlichte, B. Spliethoff, A. Wingen, S. Kaskel, J. S.
Bradley, F. Schuth, Angew. Chem. Int. Ed., 2001, 40, 4204.
110. (a) W. M. Van Rhijn, D. E. De Vos, W. D. Bossaert, J. Bullen, B.
Wouters, P. Grobet, P. A. Jacobs, Stud. Surf. Sci. Catal., 1998, 117, 183. (b)
W. M. Van Rhijn, D. E. De Vos, B. F. Sels, W. D. Bossaert, P. A. Jacobs,
Chem. Commun. 1998, 317. (c) W. D. Bossaert, D. E. De Vos, W. M.
Van Rhijn, J. Bullen, P. J. Grobet, P. A. Jacobs, J. Catal., 1999, 182,
156. (d) I. Diaz, C. Marquez-Alvarez, F. Mohino, J. Perez-Pariente, E.
Sastre, J. Catal., 2000, 193, 295.
111. D. Das, Jyh-Fu Lee, S. Cheng., J. Catal, 2004, 223, 152.
112. O. Kwon, S. Park, G. Seo., Chem. Commun., 2007, 4113.
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113. J. A. Melero, L. F. Bautista, G. Morales, J. Iglesias, D. Briones, Energy Fuels,
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Sobczak, M. Ziolek, Catal. Today, 2009, 142, 278. (b) K. R. Kloestra, H.
Van Bekkum, Stud. Surf. Sci. Catal., 1997, 105, 431.
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Chapter 1. Introduction
Ph. D. Thesis of Mr. Devaki Nandan Page 46 CSIR-IIP
Chapter 2. Techniques Used for Characterization of Lab Synthesized Materials
Chapter 2: Techniques Used for Characterization of Lab
Synthesized Materials
Characterization defines the catalyst
Ph. D. Thesis of Mr. Devaki Nandan CSIR-IIP
Chapter 2. Techniques Used for Characterization of Lab Synthesized Materials
Ph. D. Thesis of Mr. Devaki Nandan Page 47 CSIR-IIP
Chapter 2: Techniques Used for Characterization of Lab
Synthesized Materials
2.1 Introduction
Porous materials with nanometer scale exponentially gaining interest in different
scientific disciplines such as physics, chemistry and biology having their fascinating
characteristics like the nature of their framework such as crystallinity, well
defined physical and chemical properties and the tailorable porosity (high
surface area and hierarchical pore size distribution). These characteristics
fascinated their use in several application such as heterogeneous catalysis, sensor
devices, adsorption, ion-exchange, medical therapy, modification of polymers and
hosts in numerous of technical processes.1 The increasing demand of porous
materials in various fields has become possible due to the knowledge of their new
characteristics with the help of the sophisticated tools and characterization
techniques. To explore the reason behind the reactivity of catalytic sites one should
know the structure and chemical nature of the active component and its change due
to nature and structure of support or due to additives or due to preparation
variables and post preparation modification. The rapid development of the
advanced sophisticated tools and characterization techniques over the last decades
has come up to the understanding of porous material structures. These
characterization methods are Porosimetry, Temperature Programmed Desorption, X-
ray Diffraction, Scanning Electron Microscopy, Transmission Electron
microscopy, Energy Dispersive X-Ray Spectroscopy, Inductively coupled plasma
atomic emission spectroscopy, and Fourier transform infrared spectroscopy.
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Ph. D. Thesis of Mr. Devaki Nandan Page 48 CSIR-IIP
In this context, a comprehensive discussion regarding the detailed
characterization techniques used for the characterization of all the porous supports
and catalysts, synthesized throughout the research period, have been presented.
2.2 Characterization Techniques
2.2.1 Powder X-Ray Diffraction Analysis
Powder X-ray diffraction is a non destructive technique that is one of most
preliminary and powerful instrumental technique required for the characterization
of nano-porous and nano-structured materials to know about their crystalline and
porous nature. The diffraction of X-Ray arises when it interacted with a periodic
structure of crystalline material.2 In X-ray diffraction technique, a fixed wave length
(λ), is chosen for the incident radiation and Bragg Peaks are measured by observing
the intensity of the scattered radiation as a function of scattering angle 2θ. By
scanning the sample through a range of 2θ angles, all possible diffraction patterns of
the lattice should be attained due to the random orientation of the powdered material.
Conversion of the diffraction peaks to d-spacing allows identification of the
material because each material has a set of unique d-spacing. Typically, this is
achieved by comparison of d-spacing with standard reference patterns. The d spacing
is calculated from the values of the peaks observed from the Bragg's equation
(equation i). The position of the diffraction peaks gives information about the
structure of the material.
nλ = 2d sin θ ---------- i
Where, n is the order of reflection and the values are 1, 2, 3,..., λ is the
wave length of the X-ray radiation, d is the interplanar spacing between two
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successive planes and θ is the angle between the incident ray and the scattering
planes. Knowing θ, n and λ, the lattice spacing d can be easily calculated.
X-ray diffractometer consists of a circular table with a stationary X
-ray source and a moving detector, usually a proportional counter, which
records the intensity of the reflected beam as a function of the reflected angle. This
technique provides a wealth of useful information about the geometry of the crystal
lattice, specific atoms and their arrangement in the unit cell of the crystal structure,
degree of crystallinity of the sample, and allows qualitative identification of the
crystalline phase. The position and relative intensity of the lines in the X-ray
diffraction pattern serve as a finger print for a given type of crystalline
material. By comparing an X-ray diffraction pattern against the patterns
collected for known crystalline compounds, the crystallinity and porous nature
material can be determined.
X-ray line broadening of the peak shape of one or more diffraction lines
can be used to estimate the crystal size in powder materials.3 As the particle
size decreases, the reflections in the XRD pattern will be broadened. This correlation
is used in Scherrer's equation (ii) to calculate the particle size.
K cos
= iiDB
Where DB = mean crystallite diameter
K = Scherrer's constant
λ = X-ray wave length (1.5418 Å for Cu Kα radiation)
β = full width at half maximum
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θ = Bragg's angle
In addition to crystallite size of the materials, X-ray line broadening
gives information about dispersion and the degree of metal oxide present at the
surface of the support. The minimum detection limit for crystallite size is 4 nm and
the two-dimensional metal oxide over layers cannot be detected by XRD. In the
present course of work, XRD pattern of the support and catalysts were obtained on a
Bruker D8 diffractometer, with nickel filtered Cu Kα radiation (λ=1.5418 Å) with an
applied voltage and current of 40 kV and 20 mA respectively. Bruker D8
diffractometer has two detectors viz. Scintillation counter detector and lynx eye
super speed detector. Scintillation counter detector has been used for the
analysis of samples in which 2 value start below 1° known as low angle XRD
pattern. On the other hand, lynx eye super speed detector has been used to acquiring
the wide angle XRD pattern.
2.2.2 Porosimetry
N2-adsorption desorption measurement is one of the commonly used characterization
tools to determine the specific surface area, nature of pores, pore size distribution, and
to probe surface properties of porous materials.4
The amount of adsorbed/desorbed
nitrogen is measured as a function of the applied pressure, giving rise to the
adsorption/desorption isotherm. The shape of the physisorption isotherm depends
on the porous texture of the measured solid and the operational temperature.
Linearity of the isotherms is generally observed at very low surface coverage and
therefore cannot be easily detected at the higher temperatures so this techniques
normally used for studying the complete range of relative pressure P/P0 at
temperature -196 οC for nitrogen adsorption. The deviation from linearity may be
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either towards or away from the pressure axis, depending on the scale of
surface heterogeneity and the magnitude of the adsorbate-adsorbate interactions.
Figure 2.1 IUPAC classifications of different types of sorption isotherms
According to the IUPAC classification, six types of isotherms can be
distinguished as shown in Figure 2.1. Reversible Type I isotherms are given by
the microporous materials such as zeolites molecular sieves and many activated
carbons having relatively small external surface area. Type II & III isotherm is
the normal form obtained with a non-porous or macroporous adsorbents. The type II
isotherm represents unrestricted monolayer-multilayer adsorption. The type IV
isotherms are given by mesoporous adsorbents. In this case, the initial monolayer-
multilayer adsorption on the mesopores walls is followed by capillary condensation.
A characteristic feature of most Type IV and V isotherms is the appearance of
hysteresis loops (Figure 2.2). Hysteresis gives information regarding pore shapes5can
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be seen in figure 2.3. A characteristic feature of most Type IV isotherms is the
appearance of H1 or H2 hysteresis loops. The H1 loop is indicative of a
narrow range of uniform mesopores, whereas the more common H2 loop can
usually be attributed to percolation effects in a complex pore network with ink-bottle
type pores.
Figure 2.2 Hysteresis loop seen from type IV isotherm
Figure 2.3 Shape of the pore according to hysteresis loop
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2.2.2.1 BET Surface Area
BET theory was first introduced by Brunner, Emmett, and Teller in 1938.6 It is the
most widely used technique in determining surface areas by physical adsorption
of gases at their boiling temperatures. The significance of the BET theory lies in its
ability to determine the number of molecules required to form a monolayer of
adsorbed gas on a solid surface. The basic equation for finding out the surface area
by BET method is given below in eqn. (iii)
P
Va(Po - P)1
Vm C
C -1
Vm C
P
Po+= x iii
Where P is Adsorption equilibrium pressure
PO is Saturated vapour pressure of adsorbate
Va is Volume of adsorbate corresponding to pressure P
Vm is Volume of adsorbate required for monolayer coverage
And C is A constant relating to the heat of adsorption.
According to the BET method, a plot of P/Va(PO-P) against P/PO
yields a straight line when P/PO < 0.3. From the slope and intercept of the straight
line, volume of monolayer (Vm)7
can be calculated which in turn is used in
calculating the specific surface area of the catalyst:
SBET(m2/g)Vm x N
22,414 x W= x ivAm
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Where
Vm is Monolayer volume in ml @ STP
N is The Avogadro number (6.0231023)
W is Weight of the sample (g)
Am is Cross sectional area of the adsorbate molecule (0.162 nm2
for N2)
2.2.2.2 Pore Volume and Pore Size Distribution Analysis
Micropore volume and micropore size distribution of microporous zeolites materials
were usually determined by using the t-plots8 and Harvath-Kawazoe method.
9 The t-
plot method consists of a comparison of the amount adsorbed with the statistical
thickness of the adsorbed layer of a known reference isotherm at the same
relative pressure. According to Lippins, Linsen and de Boer8
the thickness t, of
nitrogen monolayer at any point of isotherm is calculated by using the equation (v).
Va
Vm= vt 3.54 Å
Where Va is the volume adsorption at pressure P, and Vm is the volume
of monolayer. A plot of Va verses t is known as the t-plot. Extrapolation of the linear
portion to the ordinate axis gives a positive intercept equivalent to the micropore
volume.
The total pore volume is calculated by measuring the volume of nitrogen
adsorbed at P/P0 near unity. At this relative pressure, adsorbate is assumed to be
condensed inside the pores of the zeolite. The measured total pore volume of zeolite
is larger than the micropore volume due to condensation of adsorbate in the
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intercrystalline voids between zeolite crystals, or, in the case of hierarchical zeolite,
in the mesopores. Thus the total pore volume is often assumed to be the sum of
micropore and mesopore volumes in the case of hierarchical zeolite materials.
The pore size distribution of mesoporous materials is based on the
capillary condensation phenomenon and its quantitative expression is given by
Kelvin's equation (eqn. vi)10
relating the adsorbate condensation pressure (Pc) to
the radius of the pore rp. The calculation method is described by Barrett, Joyner
and Halenda, hence called the BJH method.11
Pc
Po
cos
RTrm= viln
Where; γ is the surface tension of the adsorbate at the temperature T, rm
is the mean radius of curvature of the liquid meniscus (Kelvin radius), R is the perfect
gas constant, θ is the angle of contact, V is the molar volume of the liquid
(condensate), rp is the radius of the pore, t is the adsorbed layer thickness. As the
angle θ is generally assumed to be equal to zero because the nitrogen condensate
completely wets the pores, the radius of the pore (rp) and Kelvin‟s radius (rm) only
differ from each other by the thickness (t) of the adsorbed film. The equation
is enlightening with regard to hysteresis. In a straight capillary open at both ends, the
mean radius is related to the two primary radii r1 and r2.
vii1/rm = 1/2 [1/r1 + 1/r2]
only the radius r1 is operative when pores are filling (since r2 = ∞) hence rm in the
equation (eqn. vii) equals 2r1 during filling. However, when pores are emptying
rm = r1= r2. No pore, whether filling or emptying of condensate, is without
adsorptive because of the film of thickness t on the pore walls. The value of t is
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derived from an equation or from a reference isotherm. Thus when all pores are
indeed open-ended and cylindrical, eq.vi can be rewritten as follows
Ln [P/Po] = - [ V/RT(r-t )] (for the adsorption branch)
Ln [P/Po] = - [2 V/RT(r-t )] (for the desorption branch)
N2 adsorption/desorption measurements of the all samples during the
course of this research program were carried out by using BELSORB MAX, Japan
instrument and ASAP-2010 unit from Micromeritics (USA) in the relative pressure
range P/P0 from 1 x 10-6
to 1 at liquid nitrogen temperature (-196 οC).
2.2.3 Scanning Electron Microscopy (SEM)
Scanning electron microscopy technique is another powerful tool for studying the
morphological and structural features of the porous materials.12
It produces
images of the sample by scanning it in a raster pattern on the specimen
surface with a focused beam of electrons. The interaction between the electron
beam and the specimen surface produces various types of energetic emissions,
including back scattered electrons, secondary electrons, Auger electrons,
continuous X-rays, and characteristics X-rays. The electrons interact with atoms in
the sample, producing various signals that can be detected and that contain
information about the samples surface topography and composition. The image
displayed on the cathode ray tube comes from the secondary and backscattered
electrons. The secondary electrons are the excited electrons emitted from the
specimen due to bombardment of the electron beam. Scanning electron
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microscopy has a large depth of field, which allows a large amount of the sample to
be in focus at one time. The SEM also produces images of high resolution, which
means that closely spaced features can be examined at a high magnification.
Preparation of the samples is relatively easy since most SEM only require the
sample to be conductive. The combination of higher magnification, larger depth
of focus, greater resolution, and ease of sample observation makes the SEM one of
the most important tool used in research areas today. A representative SEM
image of CoFe2O4@C material has been shown in figure 2.4. A simple schematic
diagram of the SEM can be seen in Figure 2.5.
Figure 2.4 SEM image of carbon embedded CoFe2O4 nano-particles.
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Figure 2.5 A schematic diagram of the scanning electron microscope (reproduced
from http://www.purdue.edu/ehps/rem/rs/sem.htm).
In order to reveal the surface morphologies of the samples under
investigation in this study, scanning electron micrographs were obtained using a
Quanta-200F field-emission scanning electron microscope (FE-SEM) operated at
1-20 kV with an energy dispersive spectrometer (EDS) attachment. Because the
SEM utilizes vacuum conditions and uses electrons to form an image, special
preparations must be done to the sample. All water must be removed from the
samples because the water would vaporize in the vacuum. All metals are conductive
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and require no preparation before being used. All non-metals need to be made
conductive by covering the sample with a thin layer of conductive material. Samples
for SEM were prepared by adding a very minute amount of the finely powered
samples onto a carbon tape. Then the samples was coated with a film of gold and then
mounted over the probe for scanning.
2.2.4 Transmission Electron Microscope (TEM)
Transmission electron microscopy (TEM) is a vital characterization tool frequently
used for the detailed examination of nano-structured materials. It measures the
quantitative particle or grain size, size distribution, and morphology (such as shape,
geometry, and dimensions) of the nano-structured materials.13
Further, in the
analysis of mesoporous materials, TEM techniques give a clear indication of
ordered structure with long narrow channels and ordered pore openings. The
basic principle of the TEM is same as of the light microscope, but it uses electron
instead of light. Transmission electron microscopes use electrons as light source and
their much reduced wavelength make it possible to achieve resolutions of one
thousand times better than with a light microscope. Thus, objects of the order of 10-
1nm can be resolved. The typical TEM image of CoFe2O4@C is given in figure 2.6.
The schematic diagram of a transmission electron microscope is shown in Figure 2.7.
In this technique, a beam of electrons is transmitted through a sample containing
specimen and images are formed from the interaction of the electrons. Then, the
image is magnified and focused onto a fluorescent screen with the help of
electromagnetic lenses or detected by sensor such as a charge couple device
(CCD) camera. In terms of magnification and resolution, TEM has an
advantage compared to SEM. TEM has up to a 50 million magnification level
while SEM only offers 2 million as a maximum level of magnification. The
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Figure 2.6 TEM image of carbon embedded CoFe2O4 nano-particles.
Figure 2.7 A schematic diagram of the scanning electron microscope (reproduced
from http://www.britannica.com/EBchecked/topic/602949/transmission-electron-
microscope-TEM).
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resolution of TEM is 0.5 angstroms while SEM has 0.4 nanometers. However,
SEM images have a better depth of field compared to TEM produced images.
Another point of difference is the sample thickness, “staining,” and preparations.
The sample in TEM is cut thinner in contrast to a SEM sample. In addition,
SEM sample is “stained” by an element that captures the scattered electrons.
2.2.5 Energy Dispersive X-Ray Spectroscopy
Energy-dispersive X-ray spectroscopy is a qualitative and quantitative X-ray
micro analytical technique that can be used for the identification of elements and
their relative proportion in terms of atomic percentage present within the materials.
It can be combined with other imaging tools such as scanning electron microscopy
(SEM), transmission electron microscopy (TEM), and scanning transmission
electron microscopy (STEM) for the identification of the elements present on areas
as small as nanometers in diameter. As a type of spectroscopy, it relies on the
investigation of a sample through interactions between electromagnetic radiation
and matter, analyzing x-rays emitted by the matter in response to being hit
with the electromagnetic radiation. Its characterization capabilities are due in large
part to the fundamental principle that each element has a unique atomic structure
allowing x-rays that are characteristic of an element's atomic structure to be identified
uniquely from each other.
In this technique, a beam of electrons was focused on the sample
in either a scanning microscope or a transmission electron microscope. The
electrons from the primary beam penetrate the sample and interact with the
atoms as a result of which two types of X-rays "Bremsstrahlung X-rays" and
"Characteristic X-rays" were generated. The X-rays are detected by an Energy
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Dispersive Detector, which displays the signal as a spectrum, or histogram, of
intensity versus Energy. The energies of the characteristic X-rays allow the
elements making up the sample to be identified, while the intensities of the
characteristic X-ray allow the concentrations of the elements to be quantified.
2.2.6 Thermo Gravimetric Analysis (TGA)
It provides a quantitative measurement of any weight change associated with a
transition. This also provides temperature at which dehydration or
decomposition takes place. Changes in weight are a result of the rupture and/or
formation of various physical and chemical bonds at elevated temperatures that lead
to the evolution of volatile products or the formation of heavier reaction products.
From such curves, data are obtained concerning the thermodynamics and kinetics
of the various chemical reactions, reaction mechanisms and the intermediate and final
reaction products.14
. TGA is a technique by which the mass of the sample is
monitored as a function of temperature or time, while the sample is subjected to a
controlled temperature program. Thermo gravimetric analysis is mainly directed in
establishing optimum temperature ranges for drying or igniting precipitates.
However, it has a much wider potential in estimating the composition of
moisture content, solvent content, additives, polymer content and filler content. 14
DTA (Differential Thermal Analysis) analysis gives information about the
changes in phase during heating. In differential thermal analysis, the temperature
of a sample and thermally inert reference material is measured as a function of
temperature.15
Any transition that the sample undergoes will result in the liberation or
absorption of energy by the sample with a corresponding deviation of its
temperature from that of the reference. This differential temperature versus the
programmed temperature at which the whole system is being changed shows the
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transition temperature whether the transition is exothermic or endothermic. TGA
technique is employed in the present study in order to determine the thermal
stability of the zeolite framework, weight loss occur due to water removal from
zeolite lattice and the weight loss occur during the decomposition of the
organic templating agents that are used at the time of synthesis. The Diamond
Thermogravimetric/Differential Thermal Analyzer (TG/DTA) of Perkin Elmer
combines the high flexibility of the differential temperature analysis (DTA)
feature with proven capabilities of the Thermogravimetry (TG) measurement
technology. The combination not only ensures that the sample is exposed to identical
thermal treatment and environment but allows one to determine whether an
endothermic or exothermic transition is associated with weight loss in contrast to a
melting or crystallization process. Thermo-gravimetric analyzer. The thermograms
of the samples are recorded between 25-800 οC with a heating rate of 10
οC/min at atmospheric pressure. In present study the thermogravimetric analysis
was carried out by using Perkin Elmer-Pyris Diamond TG/DTA instrument.
2.2.7 Temperature Programmed Desorption (TPD)
Temperature programmed desorption (TPD) is based on the basis that stronger acid
sites require more energy to desorbs the ammonia than that of weaker acidic sites.
The acidity of the catalyst is measured by temperature programmed desorption of
NH3 (NH3-TPD) using a Micromeritics chemisorbs 2750 pulse chemisorption system
where 0.1 g sample is used for each TPD experiment. It is carried out after of the
catalyst sample is dehydrated at 300 οC in helium gas (30 cm
3min
−1) for 1 h. The
temperature is decreased to room temperature (30 οC) and NH3 is adsorbed by
exposing sample treated in this manner to a stream containing 10% NH3 in helium for
1 h at 30 οC. It is then flushed with helium for another 1 h to remove physicosorbed
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NH3. The desorption of NH3 is carried out in helium gas flow (30 cm3min
−1) by
increasing the temperature up to desired temperature 10 οC /min heating rate, to
measure NH3 desorption using TCD detector.
2.2.8 Fourier Transform Infrared Spectroscopy (FT-IR)
Fourier transform infrared spectroscopy techniques have been extensively used in
heterogeneous catalysis for the identification of various properties of the catalysts
and catalyst support, which are categorized into the following groups.16
Functional groups at the catalyst surface
Active transient species and reaction intermediates
Framework structure of the materials
Species responsible for surface modification such as catalytic poisoning
Surface acidity of the catalysts
The basic principle of this technique implies that a molecule can
exist in a variety of vibrational energy levels and can move from one level to
another by absorption/release of energy, which is equivalent to the difference in
energy of the two involved levels. The absorption/emission of an electromagnetic
radiation accomplishes these transitions and this forms a basis of vibrational
spectroscopy. A particular given transition between the two energy states usually
ground state (E0) and the first excited state (E1) can be correlated by the following
equations. From the fundamentals of IR spectroscopy the equation relating the force
constant, the reduced mass and the frequency of absorption is:
ῡ = (1/2+V) 1/2πc)√(k/µ) ----------(i)
So E = hν E = E1– E0 = hc/λ = hῡ
Chapter 2. Techniques Used for Characterization of Lab Synthesized Materials
Ph. D. Thesis of Mr. Devaki Nandan Page 65 CSIR-IIP
As chemical bond is assumed to be harmonic oscillator so from that
concept V is the vibrational quantum number may be 0, 1, 2, 3……etc. So for
fundamental IR bands E=hῡ where E is the energy difference between two
energy levels, h is Planck's c is the velocity of light and ῡ in the wave number.
The most commonly used range of infrared spectrum is between 4000 cm-
1at high frequency end and 400 cm
-1at lower frequency end. The range from
4000 to 1500 cm-1
is generally considered as the functional group region and all
frequencies below 1500 cm-1
are considered characteristic of the fingerprint region.
In the case of porous materials, this technique has been extensively used for
identifying the framework structure of the materials, as well as for identifying the
various functional groups of the support. In addition, it is also used for identifying the
various functional groups of the active component, and to measure the surface acidity
of the catalysts.16
In present study the infrared induced vibrations of the samples under
investigation were recorded using Perkin Elmer FT-IR X 1760 instrument by means
of KBr pellet procedure. In this procedure, a small amount of the sample was
mixed with KBr and finely ground to get a homogeneous mixture. This mixture
was then taken in a die and pressed under high pressure into a transparent pellet
before recording the spectra. Spectra were taken in the transmission mode and the
samples were evacuated before making the pellet and the spectra were taken under
atmospheric pressure and at temperature of 20 οC. Changes in the absorption bands
were investigated in the 400-4000 cm-1
region.
Chapter 2. Techniques Used for Characterization of Lab Synthesized Materials
Ph. D. Thesis of Mr. Devaki Nandan Page 66 CSIR-IIP
2.2.9 Inductively Coupled Plasma -Atomic Emission Spectrometry (ICP-AES)
ICP- AES is an emission spectrophotometric technique, the principle of ICP-AES is
that excited electrons emit energy at a given wavelength as they return to ground state
after excitation by high temperature Argon Plasma. The fundamental characteristic of
this process is that each element emits energy at specific wavelengths peculiar to its
atomic character. The energy transfer for electrons when they fall back to ground
state is unique to each element as it depends upon the electronic configuration of the
orbital. The energy transfer is inversely proportional to the wavelength of
electromagnetic radiation, Although each element emits energy at multiple
wavelengths, in the ICP-AES technique it is most common to select a single
wavelength (or a very few) for a given element. The intensity of the energy emitted at
the chosen wavelength is proportional to the concentration of that element in the
sample being analyzed. Thus, by determining which wavelengths are emitted by a
sample and by determining their intensities, the analyst can qualitatively and
quantitatively find the elements from the given sample relative to a reference
standard. The wavelengths used in AES ranges from the upper part of the vacuum
ultraviolet (160 nm) to the limit of visible light (800 nm). As borosilicate glass
absorbs light below 310 nm and oxygen in air absorbs light below 200 nm, optical
lenses and prisms are generally fabricated from quartz glass and optical paths are
evacuated or filled by a non absorbing gas such as Argon.
In present study Inductively Aoupled Plasma Atomic Emission
Spectroscopic (ICP-AES) analysis (model: PS 3000 uv, (DRE), Leeman Labs, Inc.,
USA) was carried out for analyzing the presence of metals in catalyst.
Chapter 2. Techniques Used for Characterization of Lab Synthesized Materials
Ph. D. Thesis of Mr. Devaki Nandan Page 67 CSIR-IIP
2.2.10 Titration Method
Standard acid base titration method was used for existence of total acidity on acid
functionalised carbon silica composite and acid functionalized nonporous carbon. In a typical
method certain amount of catalyst sample was taken and treated with concentrated NaCl
solution by which all the acidic H ions on the acidic groups was replaced by Na ions. The
filtrate (having H ions ) was titrated by NaOH solution to get the total acidity.
2.3 References
1. (a) N. K. Mal, A. Bhaumik, R. Kumar, A. V. Ramaswamy, Catal. Lett.,
1995, 33, 387. (b) C. H. Bartholomew, R. J. Farrauto., Fundamentals of
industrial catalytic processes, 2nd ed.; John Wiley & Sons:
Hoboken, N. J., 2006. (c) A. Dyer, An introduction to zeolite molecular
sieves; John Wiley & Sons: Chichester, N. Y., 1988. (d) L. Pasqua, S.
Cundari, C. Ceresa, G. Cavaletti, Curr. Med. Chem., 2009, 16, 3054. (e)
M. Hartmann, Chem. Mater., 2005, 17, 4577. (e) S. J. Kulkarni, Stud.
Surf. Sci. Catal., 1998, 113, 151. (f) M. Vallet-Regi, Chem. Eur. J., 2006,
12, 5934. (g) T. Kang, Y. Park, K. Choi, J. S. Lee, J. J. Yi, Mater. Chem.,
2004, 14, 1043.
2. H. Lip son, H. Steeple, Interpretation of X-ray Powder Diffraction
Patterns, Macmillan, London 1970, 261.
3. Patterson, A. L. Physical Reviews, 1939, 56, 978.
4. (a) Y. Sakamoto, M. Kaneda, O. Terasaki, D. Zhao, J.M. Kim, G. Stucky,
H. J. Shin, R. ryoo, Nature, 2000, 408, 449. (b) O. Franke, Günter
Schulz-Ekloff, Jiří Rathouský, Jindřich Stárek and Arnošt Zukal J.
Chem. Soc., Chem. Commun., 1993, 724. 10.
Chapter 2. Techniques Used for Characterization of Lab Synthesized Materials
Ph. D. Thesis of Mr. Devaki Nandan Page 68 CSIR-IIP
5. S. Lowell and J. E. Shields, Powder Surface Area and Porosity, 3rd Ed.
Chapman and Hall, New York, 1991.
6. S. Brunauer, P. H. Emmitt, E. Teller, J. Am. Chem. Soc., 1938, 60, 309.
7. F. rouquerol, J. Rouquerol, K. S. W. Sing, Adsorption by powders
and porous solids, Acedemic Press, London, 1999.
8. B.C. Lippens, B.G. Linsen, J.H. de Boer, J. Catal., 1964, 3, 32.
9. (a) G. Horvath, K. Kawazoe, J. Chem. Eng. Japan, 1983, 16, 470. (b) W.
D. Harkins, G. Jura, J. Am. Chem. Soc., 1944, 66, 1366.
10. S. J. Gregg, K. S. W. Sing, Adsorption, Surface Area and Porosity, 2nd
Ed., New York 1982.
11. E.P. Barrett, L.G. Joyner, P.P. Halenda, J. Am. Chem. Soc., 1951, 73,
373.
12. (a) S. Che, K. Lund, T. Tatsumi, S. Iijima, S.H. Joo, R. Ryoo, O.
Terasaki, Angew. Chem. Int. Ed. 42, 2003, 2182. (b) H. Miyata, K.
Kuroda, Adv. Mater., 1999, 11, 857.
13. (a) A. Firouzi, D. Kumar, L. M. Bull, T. Besier, P. Sieger, Q. Huo,
S. A. Walker, J. A. Zasadzinski, C. Glinka, J. Nicol, D. Margolese, G.
D. Stucky, B. F. Chmelka, Science 1995, 267, 1138. (b) A. Firouzi, F.
Atef, A. G. Oertli, G. D. Stucky, B. F. Chmelka, J. Am. Chem. Soc. 119,
1997, 3596. (c) Q. Huo, D. I. Margolese, G. D. Stucky, Chem. Mater.,
1996, 8, 1147. (d) Q. Huo, D. I. Margolese, P. Feng, T.E. Gier, P. Sieger,
R. Leon, P. M. Petroff, F. Schuth, F., G. D. Stucky, Nature, 1994, 368,
Chapter 2. Techniques Used for Characterization of Lab Synthesized Materials
Ph. D. Thesis of Mr. Devaki Nandan Page 69 CSIR-IIP
317. (e) L. Mercier, T. J. Pinnavaia, Adv. Mater., 1997, 9, 500. (f) P. V.
Braun, P. Osenar, S. I. Stupp, Nature, 1996, 380, 325.
14. C. Ying, L. V. C. Rees, Thermogravimetric studies of faujasites with
different Si/Al ratios. Zeolite, 1996, 6, 217.
15. J. Lynch, Physico-chemical Analysis of Industrial Catalysts: A Practical
Guide to Characterization. Book Technip Press, 2003, 1.
16. (a) G. Ricchiardi, A. Damin, S. Bordiga, C. Lamberti, G. Spano„,
F. Rivetti, A. Zecchina, J. Am. Chem. Soc., 2001, 123, 11409. (b) G.
Coudurier, C. Naccache, J.C. Vedrine, J. Chem. Soc., Chem. Commun.
1982, 24, 462. (c) R. K. Zeidan, V. Dufaud and M. E. Davis, J.
Catal., 2006, 239, 299. (d) A. Katz, M. E. Davis, Nature, 2000, 403, 286.
Chapter 2. Techniques Used for Characterization of Lab Synthesized Materials
Ph. D. Thesis of Mr. Devaki Nandan Page 70 CSIR-IIP
Chapter 3. Facile Synthesis of Sulfonated Nano-porous …………….Composite and Mesoporous Silica
Chapter 3: Facile Synthesis of Sulfonated Nano-porous
Carbon, Sulfonated Carbon-silica-meso Composite and
Mesoporous Silica
Renewable sources and waste materials produce cheaper materials
Ph. D. Thesis of Mr. Devaki Nandan CSIR-IIP
Chapter 3. Facile Synthesis of Sulfonated Nano-porous …………….Composite and Mesoporous Silica
Ph. D. Thesis of Mr. Devaki Nandan Page 71 CSIR-IIP
Chapter 3: Facile Synthesis of Sulfonated Nano-porous
Carbon, Sulfonated Carbon-silica-meso Composite and
Mesoporous Silica
3.1 Introduction
The concentration and pKa values of catalyst play vital role in organic
transformations, where a high density of accessible strong BrØnsted acid sites
possessing stability in aqueous environment is desired for catalyst development.1 The
use of liquid acids such as sulfuric acid for example suffers from energy inefficiency
and requires separation and recycling steps of acid waste residue. The usability of
recyclable solid materials as replacement to homogeneous acid catalysts is usually
limited due to the low density and strength of the acid sites on the solid surface.2 The
method of immobilization of homogeneous catalyst on to solid supports such as
sulfonation of activated carbon resin and metallic oxide has come up to solve the
problem of acid density, but the procedure is time consuming and involves several
preparation steps.3,4
Moreover, the immobilization of acidic functional group is
difficult and also yields low acid density.
To produce cheaper material the utilisation of low cost chemicals and waste
materials are the great choice of selection as catalyst support or template. These
sources are renewable or waste materials. The one cheaper material available is
petroleum waste coal tar which is easily available for further functionalization by acid
while other sources are the various saccharides. Using of these low cost fossil source
and saccharides leads to environment friendly concept. Further the usability of
recyclable solid materials as replacement to homogeneous acid catalysts is usually
Chapter 3. Facile Synthesis of Sulfonated Nano-porous …………….Composite and Mesoporous Silica
Ph. D. Thesis of Mr. Devaki Nandan Page 72 CSIR-IIP
limited due to the low density and strength of the acid sites on the solid surface. In the
preparation of an efficient alternative solid acid catalyst for acid attributed reactions,
in present study a simple one-step method is developed for the synthesis of a new
class of sulfonated nanoporous carbon (SNC) material containing hydrophobic carbon
moiety with hydrophilic -SO3H, -OH and -COOH groups with its high acidic
properties in one hand and sulfonated carbon silica composite (SCS) material
containing hydrophobic carbon moiety with hydrophilic -SO3H, -OH and -COOH
groups surrounded by outer silica shell in other hand. These materials are not only
suitable for further functionalization with acid or metal ions but also provide good
mechanical and thermal stability for catalytic applications.
In present study, petroleum waste coal tar was used as a cheaper and green
carbon precursor for the preparation of nano-porous carbon while glucose was used as
carbon source and structure directing precursor for the preparation of acid
functionalized carbon-silica composite material. The use of these low cost sources are
the alternative to the commonly used high cost resins, ionic surfactants and P123
block co-polymers.5
In order to prepare an efficient alternative solid acid catalyst for acid
attributed reactions, facile and simple one step synthesis of a new class of nano-
porous acid functionalized carbon, sulfonated-carbon-silica composite catalyst have
been carried out and detailed characterization and properties of materials also
investigated.
Tert-Butylation of phenol is an industrially important reaction, and its
products like 4-tert-butyl phenol (4-TBP) and 2,4-ditert-butyl phenol (2,4-DTBP) are
widely used as intermediates. Habitually 4-TBP is used to manufacture various
Chapter 3. Facile Synthesis of Sulfonated Nano-porous …………….Composite and Mesoporous Silica
Ph. D. Thesis of Mr. Devaki Nandan Page 73 CSIR-IIP
antioxidants, varnish and lacquer resins, fragrances and protecting agents for plastics.
2,4-DTBP is largely used to produce substituted triaryl phosphates6,7
. The tertiary
butylation of phenol reaction is a typical Friedel–Crafts alkylation reaction, and can
be catalyzed by a variety of acid catalysts like homogeneous Lewis acids. The
product 2,4-DTBP is highly commercially interesting because of the important
application in the production of stabilizers for PVC or UV absorbers in polyolefins.8
In general, the tertiary butylation of phenol is conventionally carried out in vapour
phase reaction at higher reaction temperatures (above 140 ºC) (Table 3.1). However,
the recent developments in novel materials giving opportunity for low temperature
liquid phase catalytic reactions.9,10
The tert-butylation reaction of phenol requires a
large space (for the interaction of bulky reactant molecules , bulky intermediates and
Table 3.1 Tertiary butylation of phenol by different catalyst in literature.
Catalyst Reaction temperature ºC Phenol conversion%
HZOP-31 70 25.1211
H-AlMCM-48 175 59.112
Sulfated titania 200 32.2013
Mesoporous Galosilicate 175 37.014
H-Y(5.2) 130 10015
HPW/MCM-41 130 9915
H-beta 130 7215
FeSBA-1 200 78.516
Ga-FSM-16 160 80.317
MCM-22 145 9418
Chapter 3. Facile Synthesis of Sulfonated Nano-porous …………….Composite and Mesoporous Silica
Ph. D. Thesis of Mr. Devaki Nandan Page 74 CSIR-IIP
the products) along with strong acid sites. It is therefore the material synthesized in
this study has been explored whether the composite catalyst possesses both of these
properties for the tert-butylation reaction of phenol.
3.2 Experimental Details
3.2.1 Reagents and Chemicals
Tetraethyl-orthosilicate (TEOS) was purchased from Merck, Germany. Sulphuric acid
was purchased from RFCL India private limited. Phenol and tertiary butanol were
purched from Merck India Ltd. while glucose was purchased from Rankem India Ltd.
Coal tar was used from petroleum waste at IIP. All chemicals were used as received.
3.2.2 Synthesis of Sulfonated Carbon
The synthesis procedure is very simple that involves drop by drop addition of
sulphuric acid (55 gm) to 10 gm of coal tar obtained from petroleum waste followed
by treatment at 100 ºC for 24 h and then carbonization of the resultant mixture in
nitrogen atmosphere at 300 ºC to facilitate the decomposition and transformation of
the petroleum waste to hydrophobic carbon residue bearing sulfonyl groups. The
catalyst material was left for 4 hours in boiling water followed by washing with cold
water to remove the weakly bound acid sites and carbon before using as a catalyst.
3.2.3 Synthesis of Sulfonated Carbon-silica Composite and Mesoporous Silica
Sulfonated carbon silica composite and mesoporous silica were synthesized by the
evaporation–induced di-constituent co-assembly method. Wherein glucose was used
as carbon source as well as templating precursor and tetra-ethyl ortho-silicate (TEOS)
as silica precursor. In a typical preparation 20 gm of glucose was dissolve in 20 ml of
deionized water then 60 gm of TEOS solution was added drop wise under stirring for
Chapter 3. Facile Synthesis of Sulfonated Nano-porous …………….Composite and Mesoporous Silica
Ph. D. Thesis of Mr. Devaki Nandan Page 75 CSIR-IIP
three hours to form a miscible gel, after complete mixing 25 gm of H2SO4 drop wise
added to this solution, after two hours the mixture was solidified and turns black due
to hydrolysis of glucose and TEOS. The final precursors have molar composition of
TEOS : 0.385 glucose : 4.8 H2O : 0.88 H2SO4, was left overnight at 100 ºC for
incomplete carbonization and sulfonation , next day the sample was carbonize at 300
ºC for four hours to get sulfonated carbon-silica-meso composite. The resulting
material was washed with hot distilled water until no sulfate ions were detected in the
washed water by using barium carbonate solution. Finally the as synthesized
composite on calcination at 600 ºC for five hours yields mesoporous silica.
3.2.4 Catalytic Application of the Synthesized Materials towards Tertiary
Butylation of Phenol
The reaction of tertiary butanol (TBA) with phenol in presence of solid acid catalyst
mainly produces three products namely 2,4- di-tertiary butyl phenol (2,4-DTBP), 4-
tertiry butyl phenol (4-TBP) and 2-tertiary butyl phenol (2-TBP) having the
decreasing size of 2,4-DTBP>4-TBP>2-TBP, as shown in Scheme 3.1. In present
study, we have applied the liquid phase phenol butylation in two manners one is in
round bottom flask and other is inside Parr reactor.
Scheme 3.1 Structure of reactants and expected products.
Chapter 3. Facile Synthesis of Sulfonated Nano-porous …………….Composite and Mesoporous Silica
Ph. D. Thesis of Mr. Devaki Nandan Page 76 CSIR-IIP
3.2.4.1 Liquid Phase Reaction in Round Bottom Flask
Phenol butylation reaction was carried out in round bottom flask equipped with reflux
condenser joint with freezing pump for the continuous water supply reaction
condition. In a round bottom flask 0.5 g of SNC or SCS catalyst (5 wt. % of Phenol+
TBA) was taken then phenol and tertiary butyl alcohol were added to it with the
molar ratio of 1:2.5, then temperature was increases up to 120 ºC and product was
collected after nine hours and used catalyst was separated by filtration, washed with
ethanol dried at 100 ºC and reused for three times.
3.2.4.2 Liquid Phase Reaction in High Pressure Parr Reactor
We have applied the synthesized material for solvent free liquid phase reaction in
Parr reactor at 130 ºC for 5 h. In a typical reaction study, 0.5 g catalyst (5 wt. % of
Phenol+TBA) was taken and transferred into Parr reactor and reactor was pressurized
upto 1 bar then temperature increased by slow heating with PID controlled program
up to 130 οC. The Phenol to TBA molar ratio was 1 : 2.5. The product was collected
after 5 hours and used catalyst was separated by filtration washed with ethanol dried
at 100 ºC and reused for four times.
3.3 Results and Discussion
3.3.1 Properties of Acid Functionalized Nano Porous Carbon Composite
The wide angle XRD pattern (Figure 3.1) of the sample shows the ordered amorphous
nature of the material. The morphology and internal structure of the material analyzed
by SEM, TEM and HRTEM images (Figure 3.2) indicate the formation of porous
carbon matrix consists of interconnected nano particles of about 10 nm. The HRTEM
image of the material shows the nano porous structure of the carbon with uniform
Chapter 3. Facile Synthesis of Sulfonated Nano-porous …………….Composite and Mesoporous Silica
Ph. D. Thesis of Mr. Devaki Nandan Page 77 CSIR-IIP
Figure 3.1 XRD pattern of material.
Figure 3.2 A) SEM, B &C) TEM and D) HRTEM images of material.
Chapter 3. Facile Synthesis of Sulfonated Nano-porous …………….Composite and Mesoporous Silica
Ph. D. Thesis of Mr. Devaki Nandan Page 78 CSIR-IIP
Figure 3.3 A) N2 adsorption-desorption isotherms and B) The BJH pore size
distribution of the material.
pore size. The porous nature of the material is further supported by N2 adsorption
desorption isotherm (Figure 3.3A). The BJH pore size distribution of the sample
clearly shows that the major contributions of pores are between 1.7 to 2.6 nm (Figure
3.3B).
Chapter 3. Facile Synthesis of Sulfonated Nano-porous …………….Composite and Mesoporous Silica
Ph. D. Thesis of Mr. Devaki Nandan Page 79 CSIR-IIP
The FT-IR spectra of the sample (Figure 3.4A) shows broad band centered
around 3,400 cm-1
representing the OH stretching along with peaks around 2929 cm-1
and 2860 cm-1
related to C–H stretching vibrations. The other band appeared around
1715 cm-1
is due to -C=O stretching and that of 1606 cm-1
is related to -OH bending.
The peaks related to -SO3H stretching and O=S=O stretching are appeared at 1207
Figure 3.4 A) FTIR and B) EDX spectra of the material.
Chapter 3. Facile Synthesis of Sulfonated Nano-porous …………….Composite and Mesoporous Silica
Ph. D. Thesis of Mr. Devaki Nandan Page 80 CSIR-IIP
cm-1
and 1040 cm-1
respectively. Overall, the FT-IR spectra indicate the presence of -
COOH, -OH, -SO3H and -CH groups in the material. The elemental analysis and
EDX analysis of the material further confirms the presence of carbon, oxygen and
sulphur (Figure 3.4 B). The origin of phenolic -OH and -COOH groups can be
attributed to the open-air synthesis procedure adopted during the simultaneous
carbonization and sulfonation of the material.
The acidity of the functionalized material is determined by acid-base titration
method (Table 3.2,) indicates significantly high acid loading occurred on the material
(as high as 4.03 m mol/g) by the sulfonation method adopted in the present study. The
composition analysis of the material described above indicates the contribution of
three functional groups responsible for this acidity, namely, -SO3H, -COOH and -OH.
Among these, the -SO3H is observed to contribute 1.43 mmol/g of acidity
(determined by CHNS and EDX analysis). Rest of the acidity (2.6 mmol/g) can be
ascribed to the combined contribution of -COOH and -OH groups. Overall, the
presence of -SO3H, -COOH and phenolic –OH groups in the material are observed to
be responsible for the creation of significantly high acidity in the carbon material.
Further, the hydrophilic nature of these functional groups on the material is also
expected to contribute to the chemical interaction with the hydrophilic reactant
Table 3.2 Textural properties and acidity of SNC material
Sample SABET a
(m2g
-1)
Vtotb
(cm3g
-1)
C%c S%
c Acid density due to
–SO3H (mmol/g)
Total
Acidityd
SNC 7.6 0.0252 59 4.57 1.43 4.03
aBET surface area.
btotal pore volume taken from the volume of N2 adsorbed at P/P0 =
0.995. CDetermined by CHNS elemental analysis.
dDetermined by acid base titration.
Chapter 3. Facile Synthesis of Sulfonated Nano-porous …………….Composite and Mesoporous Silica
Ph. D. Thesis of Mr. Devaki Nandan Page 81 CSIR-IIP
molecules to facilitate the reaction in an effective manner.19,20
The thermal stability of the material was determined by TGA analysis (Figure
3.5) which shows the initial weight loss at three places; 1) About 7 % weight loss at
190 ºC 2) about 3 % weight loss between 190-282 ºC and the major weight loss of 30
% above 282 ºC that can be ascribed to the removal of water/moisture, weekly stable
carbon moiety and carbon material respectively. The high moisture and water content
possessed by the material can be ascribed to the presence of various hydrophilic
groups. This envisions that the material is stable up to 282 ºC and is suitable for
catalytic applications.
Figure 3.5 DT/TGA spectra of the material.
Chapter 3. Facile Synthesis of Sulfonated Nano-porous …………….Composite and Mesoporous Silica
Ph. D. Thesis of Mr. Devaki Nandan Page 82 CSIR-IIP
3.3.2 Properties of Acid Functionalized Carbon-silica-meso Composite and
Mesoporous Silica
The wide angle XRD pattern of both SCS and MS shows that both the materials are
amorphous in nature (Figure 3.6). The small-angle x-ray scattering (SAXS) patterns
of the as-synthesized (SCS) and calcined (MS) samples are shown in Figure 3.7. One
broad peak signifying the average pore-center-to-pore-center correlation length is
observed in both the samples.21
However; the peak is highly intensified in MS and
indicates the significant increase in the order of the meso-structure due to the removal
Figure 3.6 Wide angle XRD patterns of SCS and MS.
Figure 3.7 Small angle XRD patterns of SCS and MS.
Chapter 3. Facile Synthesis of Sulfonated Nano-porous …………….Composite and Mesoporous Silica
Ph. D. Thesis of Mr. Devaki Nandan Page 83 CSIR-IIP
of the sulfonated carbon moiety during calcination. This is further reflected in
nitrogen adsorption-desorption isotherms of SCS and MS (Figure 3.8A).
Figure 3.8 A: N2 adsorption-desorption isotherms of MS and SCS, B: The respective
pore size distribution using BJH method are Shown.
Chapter 3. Facile Synthesis of Sulfonated Nano-porous …………….Composite and Mesoporous Silica
Ph. D. Thesis of Mr. Devaki Nandan Page 84 CSIR-IIP
The isotherms of both the samples are of type IV, characteristic of mesoporous
materials according to IUPAC Classification, but hysteresis loop of MS sample
appears to be H2 type indicating that the MS has good pore connectivity that usually
observed for large mesopores resulting from removal of sulfonated-carbon moiety.21
The pore volumes of SCS and MS are 0.52cm3/g and 0.87cm
3/g respectively, that
confirms the removal of sulfonated-carbon moiety in SCS and is responsible for
significant increase in pore volume in MS Table 3.3. This phenomenon is further
reflected in the increase in average pore diameter of the SCS from 2.6 nm to 5.3 nm
after calcination (MS) (Figure 3.8 B).
The EDX elemental analysis of samples also supported the removal of the
carbon moiety after calcination (Figure 3.9). The SEM images of samples also
support the phenomenon of removal of carbon moiety during calcination of SCS,
where the black spots representing carbon moiety observed in SCS are disappeared in
MS (Figure 3.10).
Table 3.3: Textural properties of SCS and MS, by N2 adsorption at -196 οC.
Sample SABET
m2g
-1a
SAmi
m2g
-1b
SAmc
m2g
-1c
Vtot
cm3g
-1d
Vmi
cm3g
-1e
D
nmf
SCS 779.67 240.44 539.23 0.52 0.10 2.6
MS 656.47 0 656.47 0.87 0 5.3
aBET surface area.
bmicropore surface area calculated from t-plot.
cmesopore surface area
were calculated as SABET-SAmi. dtotal pore volume taken from the volume of N2 adsorbed
at P/P0 = 0.995. emicropore volume calculated from t-plot.
fBJH adsorption average pore
diameter.
Chapter 3. Facile Synthesis of Sulfonated Nano-porous …………….Composite and Mesoporous Silica
Ph. D. Thesis of Mr. Devaki Nandan Page 85 CSIR-IIP
Figure 3.9 EDX spectra of SCS and MS.
The porous nature of SCS can be seen in TEM images Figure 3.11. In TEM images,
we can see the uniform pores are visible supports the porosity pattern of the samples
as seen in figure 3.7a.
TPD analysis of samples reveal that SCS has high acidity than that of MS
(Figure 3.12A) as SCS contains the acid group bearing carbon moiety which
disappears during calcination and absent in the resulting MS. Moreover, the SCS
exhibited acidity similar to sulfonated zirconia.22
The IR spectra of the samples show
the interaction between sulfonated-carbon moiety and mesoporous silica in SCS
(Figure 3.12B). It is known that sulfonated carbon exhibits two characteristic bands
representing -OSO3H group at 1712 cm-1
and 1207 cm-1
.23
In our study, the SCS also
exhibited a band at 1712 cm-1
, but the second one at 1207cm-1
is not distinct as it is
merged with the band at 1090 cm-1
related to silica. The additional bands obtained at
3447 cm-1
and 803 cm-1
are due to presence of –OH and SiO2 stretching vibrations.
The TGA analysis of SCS (Figure 3.13) shows weight loss at two places; 1. about 8
% weight loss below 119 ºC and 2. About 14 % weight loss between 300 ºC and 750
ºC which can be ascribed to the removal of water/moisture and carbon moiety
Chapter 3. Facile Synthesis of Sulfonated Nano-porous …………….Composite and Mesoporous Silica
Ph. D. Thesis of Mr. Devaki Nandan Page 86 CSIR-IIP
respectively. This envisions that the catalyst is stable at the chosen reaction
temperature i.e 120 ºC under solvent free conditions.
Figure 3.10 SEM images of SCS and MS.
Chapter 3. Facile Synthesis of Sulfonated Nano-porous …………….Composite and Mesoporous Silica
Ph. D. Thesis of Mr. Devaki Nandan Page 87 CSIR-IIP
Figure 3.11 TEM images of SCS.
Figure 3.12 A) TPD spectra of SCS and MS, B) FT-IR spectra of SCS and MS.
Chapter 3. Facile Synthesis of Sulfonated Nano-porous …………….Composite and Mesoporous Silica
Ph. D. Thesis of Mr. Devaki Nandan Page 88 CSIR-IIP
Figure 3.13: TGA spectra of SCS.
3.3.2.1 Proposed Mechanism for the Formation of SCS and MS
Based on the textural properties of the materials obtained (Table 3.3), we have
proposed a schematic model for the synthesis of SCS and MS (Scheme 3.2).
Tetraethyl orthosilicate and glucose vigorously hydrolyse under the synthetic
conditions to give -SiOH groups and sulfonyl groups bearing aromatic organic
moiety. This supramolecular assembly of glucose molecule helps to form the cage-
like structure inside the SiO2 where, –SO3H group acts as hydrophilic agent that can
facilitate the interaction between hydrophobic carbon moiety and the hydrophilic
silica moiety for the successful formation of SCS composite, which upon calcinations
expels the sulfonated-carbon moiety to give MS with increased average pore diameter
and pore volume (Figure 3.8B). Aggregation or even close-packing of the SiO2 can
also result in the formation of a mesoporous structure.24
Thus, SiO2 units are self assembled, and their structure effectively sustains the
local strain caused during the carbon removal and mesopore formation. Upon
calcinations, the supramolecular assembly of sulfonated sulfonated glucose molecule
Chapter 3. Facile Synthesis of Sulfonated Nano-porous …………….Composite and Mesoporous Silica
Ph. D. Thesis of Mr. Devaki Nandan Page 89 CSIR-IIP
breaks from the SiO2 structure. Contrary to the previously reported templating
pathways using surfactants or block-co-polymers where the interaction between the
template molecules and the silica framework is through hydrogen or ionic bonding,
25,26 in present study covalent bonding is observed to exist between the carbon moiety
and SiO2 of the SCS composite as it is confirmed by the presence of two IR bands at
1712 cm-1
and 1633 cm-1
representing -OSO3H ester bond and aromatic ring
respectively. As a result, the SCS of the present study exhibits pore expansion (Figure
3.8B) rather than the pore contraction (as conventionally observed for surfactants or
block-co-polymer templated materials), up on calcination.
Scheme 3.2 The proposed templating and sulfonation pathway for the synthesis of
SCS and MS.
3.3.3 Performance of the Catalysts towards Tertiary Butylation of Phenol
3.3.3.1 Liquid Phase Reaction in Round Bottom Flask
The SNC and SCS material synthesized in the present studies indicated the promising
catalytic functionality of the SNC and SCS, where, the SNC catalyst exhibited as high
as 65% conversion based on phenol (>97% conversion based on alcohol) than that of
50% for SCS catalyst (Table 3.4). If we compare the product selectivity in case of
Chapter 3. Facile Synthesis of Sulfonated Nano-porous …………….Composite and Mesoporous Silica
Ph. D. Thesis of Mr. Devaki Nandan Page 90 CSIR-IIP
SNC catalyst it was found 40.5%, 34.5% and 25% to 2,4-ditertiary butyl phenol (2,4-
DTBP), 4-tertiry butyl phenol (4-TBP) and 2-tertiary butyl phenol (2-TBP)
respectively (Table 3.3) but in case of SCS catalyst it was 18%, 30% and 52% to 2,4-
ditertiary butyl phenol (2,4-DTBP), 4-tertiry butyl phenol (4-TBP) and 2-tertiary
butyl phenol (2-TBP) respectively. The reusability of the catalyst (SCS) synthesized
in this work was investigated by filtering the reaction solution, washing with ethanol
and drying at 120 ºC between consecutive cycles. From above discussion, it can be
seen that SNC has better conversion of phenol and better selectivity towards 2,4-
DTBP. This may be ascribed due to the nonporous nature of SNC gave higher
conversion and with higher bulky molecular selectivity. The results indicate
comparable or better performance of the SNC and SCS catalyst with the reported
results (Table 3.1).
3.3.3.2 Liquid Phase Reaction in Parr Reactor
Table 3.4 Performance of the synthesized catalyst for tertiary butylation of phenol
Catalyst Reaction
time(h)
Conversion of
phenol ( mol% )
Selectivity of product ( mol% )
2-TBP 4-TBP 2,4-DTBP
SNCa 9 65 25 34.5 40.5
SNCb 9 66 24 35.0 41
SCSa 9 50 52 30 18
SCSb 9 49 53 29 18
aFresh catalyst.
bUsed catalyst after three reaction cycle
Chapter 3. Facile Synthesis of Sulfonated Nano-porous …………….Composite and Mesoporous Silica
Ph. D. Thesis of Mr. Devaki Nandan Page 91 CSIR-IIP
To see the effect of pressure the reaction was performed in high pressure Parr reactor.
The SNC catalyst exhibited as high as 85% conversion based on phenol (>98%
conversion based on alcohol) with product selectivity of 64.5%, 14.5% and 14% to
2,4-ditertiary butyl phenol (2,4-DTBP), 4-tertiry butyl phenol (4-TBP) and 2-tertiary
butyl phenol (2-TBP) respectively (Table 3.5) while SCS catalyst gave 60%
conversion with 22%, 38% and 36% to 2,4-ditertiary butyl phenol (2,4-DTBP), 4-
tertiry butyl phenol (4-TBP) and 2-tertiary butyl phenol (2-TBP) respectively.
From above discussion, It can be seen that in Parr reactor we have more
phenol conversion as well as more 2,4-DTBP selectivity then that of round bottom
flask and SNC catalyst give better performance than that of respective SCS catalyst.
This may be ascribed to due to better contact between reactant and catalyst inside
autoclave which is not possible in round bottom flask. The higher performance of the
catalyst observed in the present study in compression of reported results having
nearly similar conditions (Table 3.6) can be ascribed to the high acid density of the
Table 3.5 Catalytic performance of the materials
Sample RT
(h)
Conversion of
phenol ( wt% )
Selectivity of product
( wt% )
2-TBP 4-TBP 2,4-DTBP Unidentified
SNCa
5 85.0 14.5 14.0 64.4 7.1
SNCb
5 83.0 15.0 14.0 65.0 6.0
SCSa
5 60.0 36 38 22 4.0
SCSb
5 59.0 35 39 23 3.0
aFresh catalyst.
bUsed catalyst after four reaction cycle
Chapter 3. Facile Synthesis of Sulfonated Nano-porous …………….Composite and Mesoporous Silica
Ph. D. Thesis of Mr. Devaki Nandan Page 92 CSIR-IIP
SNC and SCS materials obtained in the single step carbonization and
functionalization adopted during the synthesis. The present materials also exhibited
much higher catalytic activity when compared to the similar –SO3H containing
supports reported in the literature. This may be due to the co-presence of the
hydrophilic –COOH and phenolic –OH groups in the carbon moiety of both the
material that is expected to play an important role in promoting the effective
interaction between hydrophilic reactants and the active sites of the catalyst. Thus the
presence of acidic -SO3H groups along with hydrophilic groups (-COOH & -OH)
present in hydrophobic carbon of present study provides a beneficial factor for the
development of the catalytic process for alkylation reactions, and the catalyst also
exhibits constant phenol conversion up to the 4 reaction cycles (Table 3.5). The
reusability of the catalyst synthesized in this work was investigated by filtering the
reaction solution, washing the spent catalyst with ethanol and drying at 120 ºC
between consecutive reaction cycles.
Table 3.6 Tertiary butylation of phenol compression with literature
This work Sulfated Fe2O3–TiO27 Solid sulfanilic acid
8
Temperature
130 ºC 120 ºCa 120 ºC
Conversion in respect of
phenol
85% - -
Conversion in respect of
TBA
˃97% ~40%b 95%
Time hours 5 9 9
Feed ratio Phenol to TBA 2 2 2
Chapter 3. Facile Synthesis of Sulfonated Nano-porous …………….Composite and Mesoporous Silica
Ph. D. Thesis of Mr. Devaki Nandan Page 93 CSIR-IIP
3.4 Conclusions
The findings of the work demonstrated a facile and single step synthesis method for
the preparation of high quality acid functionalised nano-porous carbon (SNC) and
acid functionalized carbon-silica composite materials (SCS). The novel approach of
simultaneous carbonization and sulfonation of coal tar (petroleum waste) produced
acid functionalized nano porous carbon. While simultaneous carbonization and
sulfonation of glucose in an organic silica medium, where glucose acts as a carbon
source as well as a template precursor produced SCS. The SCS is a potential source
for the mesoporous silica preparation by simple calcination. The method is cheaper
and produces thermally stable material suitable for catalytic applications involving
bulky organic transformations. Here we have achieved as high as 4.03 mm/g acidity
in SNC material responsible for as high as 85% phenol conversion in the alkylation
reaction. The porous nature of the material also reflected in the production of high
amount of bulky 2,4-DTBP (65%) product. The phenol conversion and the selectivity
towards 2,4-DTBP on the present catalysts system are observed to be highest ever
reported on the functionalized carbon materials to the best of our knowledge.
Moreover, the active material does not suffer from leaching problems and can be
efficiently reused in consecutive catalytic cycles.
3.5 References
1. M. Toda, A. Takagaki, M. Okamura, J. N. Kondo, S. Hayashi, K. Domen and
M. Hara, Nature, 2005, 438, 178.
2. M. Kitano, D. Yamaguchi, S. Satoshi, K. Nakajima, H. Kato, S. Hayashi and
M. Hara, Langmuir, 2009, 25, 5068.
Chapter 3. Facile Synthesis of Sulfonated Nano-porous …………….Composite and Mesoporous Silica
Ph. D. Thesis of Mr. Devaki Nandan Page 94 CSIR-IIP
3. S. Suganuma, K. Nakajima, M. Kitano, D. Yamaguchi, H. Kato, S. Hayashi
and M. Hara, J. Am. Chem. Soc., 2008, 130, 12787.
4. D. Yamaguchi, M. Kitano, S. Suganuma, K. Nakajima, H. Kato and M. Hara,
J. phys. Chem. C, 2009, 113, 3181.
5. S. Van de Vyver, L. Peng, J. Geboers, H. Schepers, F. de clippel, C. J.
Gommes, B. goderis, P. A. Jacobs and B. F. Sels, Green Chem., 2010, 12,
1560.
6. A. Knop, L.A. Pilato, Phenolic Resin Chemistry, Springer, Berlin, 1985.
7. A. J. Kolka, J. P. Napolitano, G. G. Elike, J. Org. Chem., 1996, 21, 712.
8 E. Modrogan, M. H. Valkenberg and W. F. Hoelderich, J. Catal., 2009, 261,
177.
9. K. J. A. Raj, M. G. Prakash and B. Viswanathan, Catal. Sci. Technol., 2011,1,
1182.
10. F. Adam, K. M. Hello and T. H. Ali, Appl. Catal., A, 2011, 399, 42.
11. K. Ojha, N. C. Pradhan, A. N. Samanta, Chemical Engineering Journal, 2005,
112, 109.
12. S. E. Dapurkar, P. Selvam, Applied Catalysis A: General, 2003, 254, 239.
13. K. R. Sunajadevi and S. Sugunan, Catalysis Letters, 2005, 99, 3.
14. A. Sakthivel and P. Selvam, Catal. Lett., 2002, 84, 1.
15. G. Kamalakar, K. Komura, and Y. Sugi, Ind. Eng. Chem. Res. 2006, 45, 6118.
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Ph. D. Thesis of Mr. Devaki Nandan Page 95 CSIR-IIP
16. A. Vinu, T. Krithiga, V. V. Balasubramanian, A. Asthana, P. Srinivasu, T.
Mori, K. Ariga, G. Ramanath, and P. G. Ganesan, J. Phys. Chem. B, 2006,
110, 11924.
17. K. Bachari, R. M. Guerroudj, M. Lamouchi, Reac. Kinet. Mech. Cat., 2011,
102, 219.
18. K. Song, J. Guan, S. Wu, Y. Yang, B. Liu and Q. Kan, Catal. Lett., 2008, 126,
333.
19. M. Hara, Top Catal., 2010, 53, 805.
20. L. Geng, Y. Wang, G.Yu, Y. X. Zhu, Catal Comm., 2011, 13, 26.
21. A. K. Patra, S. K. Das and A. Bhaumik, J. Mater. Chem., 2011, 21, 3925.
22. W. H. Chen, H. H. Ko, A. Sakthivel, S. J. Huang, S. H. Liu, A. Y. Lo, T. C.
Tsai and S. B. Liu, Catal. Today, 2006, 116, 111.
23. M. H. Zong, Z. Q. Duan, W. Y. Lou, T. J. Smith and H. Wu, Green Chem.,
2007, 9, 434.
24. (a) D. Chen, F. Huang, Y. B. Cheng and R. A. Caruso, Adv. Mater., 2009, 21,
2206. (b) J. H. Pan, H. Dou, Z. Xiong, C. Xu, J. Ma and X. S. Zhao, J. Mater.
Chem., 2010, 20, 4512.
25. C. T. Kresge, M. E. Leonowicz, W. J. Roth, J. C. Vartuli and J. S. Beck,
Nature, 1992, 359, 710.
26. V. Meynen, P. Cool and E. F. Vansant, Microporous Mesoporous Mater.,
2009, 125, 170.
Chapter 3. Facile Synthesis of Sulfonated Nano-porous …………….Composite and Mesoporous Silica
Ph. D. Thesis of Mr. Devaki Nandan Page 96 CSIR-IIP
Chapter 4. Optimization of Acid Functionalized Carbon-Silica………..…… ……Silica preparation
Chapter 4: Optimization of Acid Functionalized Carbon-
Silica Composite Structure for its Catalytic Applications &
Mesoporous Silica Preparation
Glucose concentration and interaction with silica tailors the porosity
Ph. D. Thesis of Mr. Devaki Nandan CSIR-IIP
Chapter 4. Optimization of Acid Functionalized Carbon-Silica………..…… ……Silica preparation
Ph. D. Thesis of Mr. Devaki Nandan Page 97 CSIR-IIP
Chapter 4: Optimization of Acid Functionalized Carbon-
Silica Composite Structure for its Catalytic Applications &
Mesoporous Silica Preparation
4.1 Introduction
Acidity is an important parameter in catalyst development, where the liquid acids
such as H2SO4, HF and H3PO4 have been proven as efficient catalysts for various
industrial processes by virtue of their higher pKa values and their efficient interaction
with the reactant molecules. However, the toxicity and corrosive nature of the liquid
acids are demanding alternative sources especially those of solid acids that are having
advantage of easy separation from the product, reusability for recycle operation and
their environment friendly nature.1 But, the main limitation in using solid acids lies in
their lower density and strength of acid sites. Moreover, the accessibility of the
reactant to the active sites and their stability in the aqueous environment need to be
established. In order to take advantage of the positive aspects of liquid acids and solid
acids, the method of immobilization of liquid acids on to the solid support, viz.
sulfonation of activate carbon or metal oxides, came into practice in recent years that
provides high acid functionality bearing solid materials for catalytic applications.2
In present study, we have adopted a novel approach of simultaneous
carbonization and sulfonation of glucose in the presence of organic silica (TEOS),
where glucose act as cheaper carbon source as well as structure directing precursor
through sulfonation for the formation of the acidic sulfonated carbon-silica-meso
composite material as described in previous chapter. The previous work inspired us to
study the role of various synthesis parameters such as the concentration of glucose,
Chapter 4. Optimization of Acid Functionalized Carbon-Silica………..…… ……Silica preparation
Ph. D. Thesis of Mr. Devaki Nandan Page 98 CSIR-IIP
sulphuric acid and the method of treatment (thermal or hydrothermal) used for
facilitating interaction between carbon and silica moiety in the SCS material. In
present study various SCS materials has been prepared exhibiting wide range of
properties such as morphology, surface area, porosity and acidity that are expected to
exhibit different catalytic properties. The composite material possessing high surface
area and acidic properties is not only suitable for further functionalization with acid
or metal ions but also provides good mechanical and thermal stability for catalytic
applications.
The production of biodiesel is continuously gaining importance due to its
biodegradable, non-toxic and renewable nature, which is relevant to the present
scenario of call out for the alternative fuels to the traditional fossil fuels. The process
of biodiesel formation involves transesterification reaction between vegetable oils or
animal fats and methanol in the presence of an acid or a basic catalyst, where huge
amount (~10wt%) of glycerol is produced as unavoidable bi-product.3 The properties
of glycerol such as diesel- immiscibility make it not suitable even for fuel blending
and research is on for value addition of glycerol through its chemical conversion to
useful products and to find new applications for this cheap and off grade glycerol
obtained from biodiesel plants. Wide variety of chemicals and fuel blending stocks
were reported to produce from glycerol through the chemical reactions;4 selective
oxidation for dihydroxyacetone, glyceraldehyde, glyceric acid, glycolic acid,
hydroxypyruvic acid, mesoxalic acid, oxalic acid and tartronic acid; reduction for 1,3-
propanediol; and 1,2-propanediol; hydrogenolysis for propylene glycol; dehydration
for acrolein or 3-hydroxypropionaldehyde; halogenation for 1,3-dichloropropanol;
fermentation for 1,3-propanediol; polymerization for polyglycerols and polyglycerol
esters (Table 4.1).
Chapter 4. Optimization of Acid Functionalized Carbon-Silica………..…… ……Silica preparation
Ph. D. Thesis of Mr. Devaki Nandan Page 99 CSIR-IIP
The production of oxygenates from glycerol gains much importance due to
the excellent diesel-blending property of the oxygenates that not only improve the
quality of the fuel but also increases the overall yield of the biodiesel in helping to
meet the target for energy production from renewable sources for transport in the
energy utilization directive. Olefins such as butene or alcohols such as tertiary butyl
alcohol are commonly used as etherifying agents of glycerol, but the main drawback
involved in the use of olefin is the formation of undesired di-olefins and the
formation of huge amount of water in case of using alcohols.12
Esterification with low
molecular weight acids, transesterification with low molecular weight esters and
acetalization with aldehydes or ketones are the other promising and economically
viable alternative routes for the conversion of glycerol.13
Acetalization with ketones,
especially acetone is gaining importance due to the fact that acetone is widely
produced from biomass conversion as well as from the chemical process of cumene
Table 4.1 Value added products from glycerol conversion
Catalyst Reactant Con.% product Selectivity Ref
AC1 @ Bi/Pt (.9) Glycerol 87-97 dihydroxyacetone 50-88 5
[email protected]%Au NaOH &
Glycerol
100 glyceric acid 92 6
0.8%Ce-1.5%Bi-
0.75%Pt-3%Pd/C
Glycerol 100 tartronic acid 58 7
2.7Pt/NaY Aq Glycerol
& H2
98.7 1,2-propanediol 95.9 8
CuCr2O4 Glycerol - propylene glycol 73 9
CsPW Glycerol 100 acrolein 98 10
CeBiPt/C Glycerol polyglycerols 11
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Ph. D. Thesis of Mr. Devaki Nandan Page 100 CSIR-IIP
cracking. Hence, facilitating reaction between two biomass derived products glycerol
and acetone is advantageous as they constitute an excellent component for the
formulation of gasoline, diesel and biodiesel fuels. These oxygenated compounds,
when incorporated into standard diesel fuel, have led to a decrease in particles,
hydrocarbons, carbon monoxide and unregulated aldehyde emissions. Likewise, these
products also can act as improvers of cold flow and flash point properties of biodiesel
along with simultaneous reduction its viscosity desirable for fuel applications.13b
The main challenge involved in glycerol acetalization is the production of
water, which has to be removed in order to hinder the reversibility of the reaction.
Continuous processes for the formation of solketal employing heterogeneous
catalysts, such as the commercial macro porous acid resins of the Amberlyst family,
have been described by in the literature.13a
More recently, G. Vicente et al.13d
reported
the suitability of sulfonic meso-structured silica as a catalyst for the acetalization of
glycerol. Wider pores, large specific surface area, a relatively hydrophobic surface
and the amount of accessible acid sites were identified as the factors that positively
influence the catalytic performance in this reaction. In the present study, we would
like to explore the applicability of the SCS materials synthesized by using glucose
alone as carbon source as well as templating precursor and to understand the effect of
various synthesis parameters on the properties of catalyst materials and their role in
solketal synthesis. The concentration of glucose and method of synthesis were varied
to see the effect on the final material. In addition to the SCS materials, the study also
focus on the synthesis of hierarchical mesoporous silica (HMS) exhibiting a range of
porosity properties tuneable for the desired applications such as organic mass
transformations, adsorption of gases and immobilization of different organic moieties
Chapter 4. Optimization of Acid Functionalized Carbon-Silica………..…… ……Silica preparation
Ph. D. Thesis of Mr. Devaki Nandan Page 101 CSIR-IIP
and inorganic metals,14
by varying the glucose concentration in the initial synthetic
mixture followed by the simple calcination of the SCS composite materials.
4.2 Experimental Details
4.2.1 Reagents and Chemicals
Tetraethyl-orthosilicate (TEOS) was purchased from Merck, Germany. Glucose,
Sulphuric acid, Glycerol and Acetone was purchased from RFCL India private
limited. All chemicals were used as received.
4.2.2 Synthesis of sulfonated Carbon-silica Meso Composite and Mesoporous
Silica Materials
Two different methods have been adopted for the synthesis of various sulfonated
carbon silica composite materials (Scheme 4.1). While both the methods follow the
similar procedure and composition of the gel precursors, the main difference lies in
adopting thermal or hydrothermal treatment for controlling extent of interaction
between carbon and silicon species. In a typical synthesis procedure, a solution
obtained by dissolving 20 g of glucose in 20 g de-ionized water was added drop-wise
to the 60 g TEOS solution, followed by drop-wise addition of 23 g of concentrated
sulphuric acid (98%). The solutions were continuously under vigorous stirring
throughout the procedure and the resultant mixture was further allowed for mixing
under stirring for 3 h. The synthesis procedure is common in both the methods up to
this stage while the procedure differs in the following steps. In the thermal treatment
method, the dry gel thus obtained was heated at 120 οC for 12 h in air. On the other
hand, in the second method the gel obtained in the first step was treated inside the
Teflon-lined autoclave at 150 οC for 15 h for hydrothermal synthesis. The ramping
Chapter 4. Optimization of Acid Functionalized Carbon-Silica………..…… ……Silica preparation
Ph. D. Thesis of Mr. Devaki Nandan Page 102 CSIR-IIP
Scheme 4.1 Schematic for the synthesis of materials.
method is used to achieve the temperature (150 οC) maintained by P. I. D. Controller,
where the gradual raise in temperature was carried out with the rate 2.5 οC per minute
and the targeted temperature of 150 οC was achieved in 1h. The third step is common
in both the methods, wherein the resultant solid black mass was treated at 300 οC for
4 h under nitrogen atmosphere to obtain the solid form of sulfonated carbon-silica-
meso composite material. The materials were washed with ample amount of cold-
followed by hot deionized water until no sulphate ions appeared in filtrate solution
(by checking with barium hydroxide solution) and dried at 120 οC temperature for 12
h. The materials synthesised by first method are denoted as sulfonated carbon-silica-
meso composite (SCS) and the materials synthesised by second method are denoted
as hydrothermally treated sulfonated carbon-silica-meso composite (HSCS). Since,
glucose is the carbon source as well as structure directing agent, the concentration of
glucose is varied in both the methods to understand its role in the carbonization and
final properties of the materials. The materials thus obtained are denoted as SCS1/0.3,
SCS1/1, SCS1/2, HSCS1/0.3, HSCS1/1 and HSCS1/2, where the numeric value
Chapter 4. Optimization of Acid Functionalized Carbon-Silica………..…… ……Silica preparation
Ph. D. Thesis of Mr. Devaki Nandan Page 103 CSIR-IIP
indicates the weight ratio of TEOS/glucose taken in the synthesis mixture. Since, the
use of sulphuric acid is for the sulfonation of the carbon moiety, the molar ratio of
glucose to sulphuric acid was kept constant for the synthesis of all the materials. The
SCS and HSCS samples synthesized by the above mentioned methods are acted as
potential source for the production of hierarchical mesoporous silica (MS) materials
that are formed by simple calcination of the SCS/HSCS at 600 οC for 10 h.
4.2.3 Application of Synthesized Composite Materials for Solketal Synthesis
All the synthesized composite materials were used for acetalization of
glycerol with acetone to yield solketal (scheme 4.2). In a typical experiment, 0.25 g of
catalyst (5% of glycerol weight) was taken in a round bottom flask and 18.91 g of
acetone and 5 g of glycerol with glycerol to acetone molar ratio 1:6 was added to it
and the mixture was refluxed at 70 οC for different time duration viz. from 30 min to
4 h. After reaction was completed products were analysed by GC.
Scheme 4.2 Structure of reactants and products.
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4.3 Results and Discussion
Carbonization and sulfonation are the two important steps that influence the nature
and properties of the sulfonated carbon-silica composite materials. The rate and
extent of carbonization also influence the amount of sulfonyl bearing groups on the
carbon moiety which are related with the acidity of the final material. Due to these
reasons, the strategy adopted in the present study is related to the change in
concentration of the carbon precursor, glucose and the conditions to facilitate
effective interaction between carbon and silicon species during the simultaneous
carbonization and sulfonation synthesis. The variation in glucose concentration is also
expected to alter the material quality due to the fact of the structure directing property
of its intermediate species. To know the effect of glucose on the properties of
materials such as acidity, porosity and surface area we have varied the glucose
concentration while keeping the TEOS concentration constant. Further, to facilitate
the effective interaction between carbon and silicon species, we have adopted
additional step of hydrothermal treatment of the reaction mixture so as to improve the
simultaneous sulfonation and carbonization.
4.3.1 Effect of Synthesis Conditions on Material Properties
The influence of synthesis conditions, such as the amount of glucose and
concentration of sulphuric acid, on the morphology of SCS, HSCS are investigated.
The SEM images of the samples prepared by varying glucose concentration and
synthesis method have been given in Figure 4.1. The SCS samples synthesized by
thermal method exhibited non-uniform (hierarchical) morphology of agglomerated
spheres in the composite, while those of hydrothermally synthesised samples (HSCS)
appeared in uniform spherical morphology. Among the hydrothermally treated
Chapter 4. Optimization of Acid Functionalized Carbon-Silica………..…… ……Silica preparation
Ph. D. Thesis of Mr. Devaki Nandan Page 105 CSIR-IIP
samples, the sample HSCS 1/0.3 exhibits smoothly surfaced spherical agglomerates
that may be due to the excess amount of silica species that superfluous to generate
sufficient primary silica particles on the surface besides its interaction with carbon in
the carbon silica composite material. At higher glucose concentrations the material
(HSCS1/2) exhibited cracked sphere morphology that is attributed to the formation of
thinner outer shell prone to breakage. The above results demonstrated that the shell
morphology of composite material could be easily controlled by adjusting the ratio of
glucose to silica concentration. However, a commonality observed in both the
methods (SCS as well as HSCS) is the increase in agglomerate size with glucose
concentration. The IR spectra of the samples shows the interaction between silica and
carbon moiety in both SCS and HSCS materials (Figure 4.2 A and B). It is known
that sulfonated carbon exhibits two characteristic bands representing the –OSO3H
group at 1712 cm-1
and 1207 cm-1
.15
In our study, all the SCS and HSCS samples also
exhibited a band at 1712 cm-1
, but the second one at 1207 cm-1
is not distinct as it is
merged with the band at 1090 cm-1
related to silica. Further as the synthesis of
material was carried out in air, there is a fair chance for the oxidation of glucose in
presence of concentrated sulphuric acid to form the –COOH groups. Thus, the band at
1712 cm-1
obtained for the materials may also due to stretching vibration of (C=O) of
-COOH group. The additional bands obtained at 3447 cm-1
and 803 cm-1
are due to
presence of –OH and SiO2 stretching, vibrations. The presence of aromatic carbon is
confirmed by the presence of band at 1620 cm-1
.
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Ph. D. Thesis of Mr. Devaki Nandan Page 106 CSIR-IIP
Figure 4.1 SEM images of the materials synthesized by thermal method (A, B and C)
and hydrothermal methods (D, E and F).
Chapter 4. Optimization of Acid Functionalized Carbon-Silica………..…… ……Silica preparation
Ph. D. Thesis of Mr. Devaki Nandan Page 107 CSIR-IIP
Figure 4.2 FT-IR spectra of synthesised materials (A) SCS and (B) HSCS.
Chapter 4. Optimization of Acid Functionalized Carbon-Silica………..…… ……Silica preparation
Ph. D. Thesis of Mr. Devaki Nandan Page 108 CSIR-IIP
4.3.2 Porosity and Acidic Properties of the Synthesized Materials
Small angle X-ray diffraction patterns of the samples (Figure 4.3) reveal the presence
of larger meso-porosity in the synthesized materials.16
Textural properties of the
materials given in table 4.2 reveal that the materials synthesised by thermal method
(SCS) exhibit higher surface area and micropore surface areas compared to those
Figure 4.3 low angle XRD of various synthesized materials.
Chapter 4. Optimization of Acid Functionalized Carbon-Silica………..…… ……Silica preparation
Ph. D. Thesis of Mr. Devaki Nandan Page 109 CSIR-IIP
synthesised by hydrothermal method (HSCS). However, a common feature observed
in both SCS and HSCS materials is the increase in the micropore surface area with
the glucose concentration that is indeed expected from the formation of more
microporous carbon material with increasing carbon source, glucose in the synthesis
mixture. Accordingly, except SCS 1/1, the percentage of mesoporous surface area is
lower in SCS materials (Table 4.2). The nitrogen adsorption–desorption isotherms of
Figure 4.4 (A) and (C) N2 adsorption–desorption isotherms of the samples of SCS
and HSCS respectively (B) and (D) is the respective pore size distribution using BJH
method.
Chapter 4. Optimization of Acid Functionalized Carbon-Silica………..…… ……Silica preparation
Ph. D. Thesis of Mr. Devaki Nandan Page 110 CSIR-IIP
SCS samples (Figure 4.4A) indicate that the hysteresis loop representing mesopores
is not H1 type (observed for larger mesopores) in SCS1/0.3, but it is shifted to H1
type with increasing glucose concentration (as in case of SCS1/1 and SCS1/2). In
SCS 1/0.3 the hysteresis loop was broad with range of nitrogen adsorption volume
from 0.2–0.7 P/P0 (relative pressures) signifying the presence of small mesopores.
But in case of SCS1/1, the hysteresis loop representing the range of nitrogen
adsorption volume shifted to higher level (0.6–1.0 P/P0) signifying the presence of
meso-porosity with larger mesopores.16
However, further increase of glucose concentration as in case of SCS1/2 could
not continue this increase rather decrease in area of hysteresis loop was observed.
There seems an optimum amount of glucose required in SCS material, for its effective
interaction with silica species to form larger pores where, the concentration of
glucose used in SCS1/1 (with equal wt. ratios of glucose and TEOS) produced the
material with best porosity properties. This phenomenon is also supported by the pore
size distribution of corresponding samples (Figure 4.4B) where the average pore
diameter of SCS1/0.3 was 2.6 nm which is initially increased with glucose
concentration to 5.6 nm in SCS1/1, while further increase in glucose concentration
resulted in reversible effect of decrease in the size to 3 nm in SCS1/2 sample. Overall,
sample SCS1/1 exhibited superior properties in terms of porosity and average pore
size. Unlike this, all the three materials synthesized by hydrothermal method (HSCS)
exhibited uniform pores of type IV with H1 type hysteresis loop configuration
representing the larger mesopores (Figure 4.4C). The presence of larger mesoporosity
was evident from the sharp uptakes of nitrogen volume adsorbed at relative pressures
of 0.7–0.1.0 P/P0 as a result of capillary condensation inside the mesopores
HSCS1/0.3. Increase in the glucose concentration resulted in significant change in
Chapter 4. Optimization of Acid Functionalized Carbon-Silica………..…… ……Silica preparation
Ph. D. Thesis of Mr. Devaki Nandan Page 111 CSIR-IIP
loop configuration where the area inside the loop is decreased in both HSCS1/1 and
HSCS1/2 samples. This phenomenon is also supported by pore size distribution of the
corresponding materials (Figure 4.4D) where ordered and larger mesopores are
formed (average pore diameter (13.8 nm) at low glucose (SCSS1/0.3) concentrations.
But, increase in glucose concentration resulted in change from ordered mesopores to
hierarchical mesopores of lower pore diameter (average pore diameter of 5.7-5.9 nm),
and the hierarchy of the pores is further increased with glucose concentration
(SCSS1/2). It is interesting to see, at same glucose concentrations, the materials
synthesized by hydrothermal method exhibited larger pore diameter. For example, the
average pore diameter of the HSCS1/0.3 is 13.8 nm against 2.6 nm of the SCS1/0.3.
Table 4.2 Textural properties of the synthesized composite materials.
Sample SABET a
(m2g
-1)
SAmi b
(m2g
-1)
SAmes c
(m2g
-1)
SAmes
(%)
Vtot d
(cm3g
-1)
Vmi e
(cm3g
-1)
Df
(nm)
SCS1/0.3 779 240 539 69.19 0.52 0.10 2.6
SCS1/1 426 166 260 61.03 0.61 0.07 5.6
SCS1/2 425 274 151 35.52 0.32 0.11 3.0
HSCS1/0.3 238 21 217 91.17 0.82 0.00 13.8
HSCS1/1 176 82 94 53.40 0.25 0.03 5.9
HSCS1/2 242 119 123 50.82 0.35 0.04 5.7
aBET surface area.
bmicropore surface area calculated from t-plot.
17
cmesopore surface
area were calculated from (a-b). dtotal pore volume taken from the volume of N2 adsorbed
at P/P0 = 0.995. emicropore volume calculated from t-plot.
fBJH adsorption average pore
diameter.
Chapter 4. Optimization of Acid Functionalized Carbon-Silica………..…… ……Silica preparation
Ph. D. Thesis of Mr. Devaki Nandan Page 112 CSIR-IIP
Figure 4.5 TEM images of the materials synthesized by thermal method and
hydrothermal method.
The porous nature of SCS and HSCS samples is supported by TEM images
Figure 4.5. TEM images shows that SCS1/0.3 and SCS1/1 has uniform porosity while
SCS1/2 has hierarchical porosity in thermally prepared samples. Same trend can be
seen for hydrothermally prepared samples but size of the pores are higher in this case.
The properties of hierarchical mesoporous silica (HMS) samples obtained by
simple calcination of corresponding composite material (for removal of carbon
moiety Table 4.3) indicates that average pore diameter as well as the percentage of
meso pore surface area of the materials increased after the removal of carbon moiety.
This observation suggests that the carbon moiety is surrounded by silica moiety in the
omposite material. Further, increase of glucose concentration in the initial gel resulted
in increase in average meso pore diameter of the resultant HMS.
Chapter 4. Optimization of Acid Functionalized Carbon-Silica………..…… ……Silica preparation
Ph. D. Thesis of Mr. Devaki Nandan Page 113 CSIR-IIP
The acidity of the synthesized composite samples is measured by four
methods; elemental sulphur analysis by CHNS (Table 4.4), EDX analysis (Figure
4.6), Temperature programmed desorption of ammonia (Figure 4.7) and acid-base
titration (Table 4.4). The common trend of increase in acidity of the composite
materials with the glucose concentration was observed for all the samples, further, the
acidity related to –SO3H groups of the samples is lower than the total acidity
measured by titration method. This may be due to the contribution of other functional
groups (-COOH, phenolic – OH), which is supported by IR analysis. But, the only
difference observed between the properties of the materials synthesized by two
methods is increase in acidity is significant in the materials synthesised by
Table 4.3 Textural properties of mesoporous silica with tunable properties.
Sample SA a
(m2/g)
SAb
(m2/g)
SA c
(m2/g)
% SA
( m2/g)
Vtotd
(cm3/g)
Vmie
(cm3/g)
Vmcf
(cm3/g)
D g
(nm)
HMS1/0.3h 656 0 656 100 0.87 0.0 0.87 5.3
HMS1/1h 419 41 378 90 0.66 .01 0.65 6.6
HMS1/2h 345 11 334 96 0.67 .001 0.669 7.7
HMS1/0.3i 388 36 362 93 1.58 0.01 1.57 17.3
aBET surface area,
bmicropore surface area calculated from t-plot,
cmesopore surface area
were calculated from (a-b), dtotal pore volume taken from the volume of N2 adsorbed at
P/P0 = 0.995, emicropore volume calculated from t-plot,
fmesopore volume were calculated
as Vtot -Vmi, gBJH adsorption average pore diameter,
h and
iare the hierarchical
mesoporous silica are synthesized by thermal method and hydrothermal method
respectively.
Chapter 4. Optimization of Acid Functionalized Carbon-Silica………..…… ……Silica preparation
Ph. D. Thesis of Mr. Devaki Nandan Page 114 CSIR-IIP
Figure 4.6 The EDX spectra shows the presence of sulphur in all the synthesized materials.
hydrothermal method (HSCS) when compared to those synthesized by thermal
method (SCS).
TGA analysis of the composite materials synthesized by thermal and
hydrothermal methods (Figure 4.8) shows weight loss at two places: (1) below 100 οC
due to the removal of moisture and (2) between 300 οC and 750
οC due to the removal
of carbon material from the composite material. The above discussion envisions that
the catalysts are stable at the chosen reaction temperature i.e. 70 οC under solvent free
conditions.
Chapter 4. Optimization of Acid Functionalized Carbon-Silica………..…… ……Silica preparation
Ph. D. Thesis of Mr. Devaki Nandan Page 115 CSIR-IIP
Figure 4.7 TPD spectra of synthesised (A) SCS and (B) HSCS materials.
Chapter 4. Optimization of Acid Functionalized Carbon-Silica………..…… ……Silica preparation
Ph. D. Thesis of Mr. Devaki Nandan Page 116 CSIR-IIP
Figure 4.8 TGA spectra of synthesised (A) SCS and (B) HSCS materials.
4.3.3 Plausible Mechanism for the Formation of SCS, HSCS and HMS Materials
Based on the surface area and porosity, morphology of the materials obtained by
SEM images and acidity trends observed in TPD analysis of the composite materials
we have proposed a schematic model for the formation of SCS and HSCS materials
Table 4.4 Elemental composition and acid density of the synthesised materials
Sample Carbon % Hydrogen
%
Sulfur % Acid density due to
-SO3Ha (mmol/g)
TODb
(mmol/g)
SCS1/0.3 22.96 1.93 0.36 0.11 0.90
SCS1/1 30.59 1.79 0.45 0.14 1.20
SCS1/2 48.28 2.18 0.58 0.18 1.35
HSCS1/0.3 25.70 1.45 0.20 0.06 1.05
HSCS1/1 33.38 1.86 0.21 0.06 1.50
HSCS1/2 42.53 1.58 0.23 0.07 2.25
aCalculated from sulfur content assuming all S atoms are in the SO3H form.
bTotal acid
density determined by acid base titration.
Chapter 4. Optimization of Acid Functionalized Carbon-Silica………..…… ……Silica preparation
Ph. D. Thesis of Mr. Devaki Nandan Page 117 CSIR-IIP
obtained by thermal and hydrothermal routes (Scheme 4.3). The TEOS and Glucose
undergo hydrolysis in presence of sulphuric acid to produce the silica and carbon
species in the first step, which is common in both thermal and hydrothermal methods.
However, the direct interaction between hydrophobic carbon species and hydrophilic
silica species is not possible. Here, sulphuric acid can act as sulfonation agent and the
interaction of sulphuric acid with unsaturated cyclic carbon moiety creates the
polarity in the molecule. This supramolecular assembly of glucose molecules helps to
form the cage-like structure inside the SiO2, where otherwise difficult interaction
between hydrophobic carbon moiety and hydrophilic silica moiety is facilitated by the
presence of hydrophilic -SO3H functional groups on the hydrophobic carbon moiety
for the successful formation of the composite.18
In the present synthesis, there is no
structure directing agent is used in the initial gel mixture, but the sulfonyl carbon
Scheme 4.3 plausible mechanisms for the formation of SCS, HSCS and HMS
materials.
species formed by the sulphuric acid treatment of glucose in the initial gel itself acts
as structure directing agent and its further interaction with silica species facilitates the
formation of mesopores (carbon-silica-composite material). Hence, the high amount
of mesopores formed in the hydrothermal method gives indirect evidence to the better
Chapter 4. Optimization of Acid Functionalized Carbon-Silica………..…… ……Silica preparation
Ph. D. Thesis of Mr. Devaki Nandan Page 118 CSIR-IIP
interaction between carbon and silica moiety. The extent of carbonization of the
carbon moiety and its interaction with silica moiety is strongly influenced by the
concentration of sulfonyl group functionalized on the carbon moiety. Hence, the key
factor in the synthesis of composite material seems to be governed by the
carbonization and sulfonation reactions, where thermal and hydrothermal methods
adopted (in the second step of the synthesis) in the present study were observed to
influence the properties of the material. As shown in scheme 4.3, compared to
thermal method, the hydrothermal method adopted in step 2 of the synthesis
facilitates effective sulfonation of the carbon moiety due to the presence of the
autogenous pressure created in the autoclave that results in enhanced interaction
between carbon and silicon moieties. Third step is common in both the methods,
where the solid materials obtained in the second step are treated at high temperatures
under nitrogen atmosphere for the complete carbonization of the materials to obtain
sulfonyl functionalized thermally stable carbon-silica composite materials. As shown
in scheme 4.3, the carbonization step yields different type of materials in two
different methods, where, the effective interaction of sulfonyl groups with carbon
moiety facilitated in hydrothermal method yields homogenously distributed sulfonyl
interacted carbon-silica composite (HSCS) with larger mesopores, while the thermal
method results in the formation of heterogeneously distributed carbon having
localized carbon moieties along with silicon interacted carbon responsible for
formation of considerable micropores and smaller mesopores in SCS materials. The
fourth and final step is the production of mesoporous silica from the composite
materials by thermal treatment to remove the carbon moiety in the composite
material, where both HSCS and SCS materials produced hierarchical mesoporous
Chapter 4. Optimization of Acid Functionalized Carbon-Silica………..…… ……Silica preparation
Ph. D. Thesis of Mr. Devaki Nandan Page 119 CSIR-IIP
silica (HMS), with only difference of producing larger mesopores in hydrothermal
method and smaller mesopores in thermal method.
From above discussions, the hydrothermal method seems to be better to
synthesize the composite material (HSCS) with larger mesopores and higher acidity
required for the catalytic transformation of bulky molecules. However, the presence
of micropores and the low diameter mesopores in SCS 1/0.3 resulted in high surface
area of this material. Hence, this material also exhibits lower average pore diameter
values that further confirm the presence of carbon/carbon-silica inside the silica shell
which finds applications in catalysis due to its high surface area and hierarchical
porosity.
4.3.4 Performance of SCS and HSCS Materials towards Solketal Production
All the composite materials synthesized in this study have been tested for glycerol to
solketal reaction under similar conditions by taking reactant mixture in the round
bottomed flask attached with reflux condenser at 70 0C reaction temperature and
glycerol/acetone molar ratio of 1/6. In a typical reaction conducted on HSCS1/2
indicated the gradual increase of conversion from 30% to 82 up to the reaction time
of 30 minutes and the conversion levels are stabilized and no further change in these
values observed with reaction time (Fig. 4.9). Hence, the reaction time of 30 minutes
is considered for equilibrium attainment of the reaction and the product is collected
after this time period on all the catalysts. A blank reaction conducted in the absence
of catalyst ascertained that there is no production of solketal. Among the various
catalysts, the highest glycerol conversion of 82% along with 99 % selectivity to
solketal was obtained over the HSCS1/2 (Table 4.5). The highest conversion of
glycerol observed on HSCS1/2, despite of its lower porosity and low surface area
Chapter 4. Optimization of Acid Functionalized Carbon-Silica………..…… ……Silica preparation
Ph. D. Thesis of Mr. Devaki Nandan Page 120 CSIR-IIP
Figure 4.9 Performance of a typical composite catalyst with reaction time.
Table 4.5 Catalytic activity and product distribution with time.a
Catalyst Conversion (%) Solketal Sel. (%) TOF/hb
SCS1/0.3 76 95 39
SCS1/1 79 76 37
SCS1/2 75 90 30
HSCS1/0.3 79 98 35
HSCS1/1 80 98 32
HSCS1/2 82 99 30
Amberlyst-1531 85.1 -
a0.25 g of catalyst (5% of glycerol weight) was taken in a round bottom flask and 18.91g of
acetone and 5 g of glycerol with glycerol to acetone molar ratio 1:6 was added to it and
reflux at 70 0C for 30 min. bTOF value is based on the moles of the glycerol converted per
mole of total acid site per h.
Chapter 4. Optimization of Acid Functionalized Carbon-Silica………..…… ……Silica preparation
Ph. D. Thesis of Mr. Devaki Nandan Page 121 CSIR-IIP
indicate that the mesopores size alone is not responsible for the catalytic activity of
these composite materials. Since, the reaction under study is of acid catalyzed nature,
the catalytic activity of the materials may be related with the acidity of the samples.
The acidity patterns given in TPD spectra and total acidity measured by NaOH
titration indeed indicate the highest activity exhibiting sample HSCS1/2 also exhibits
highest acidity that supports the direct role of acidity in catalytic activity. All other
composite materials also exhibited the higher conversion values of > 75 % (lower
when compared to HSCS1/2) of glycerol. A general trend observed in catalytic
activity is that the hydrothermally treated composite materials (HSCS) outperformed
the corresponding samples prepared by thermal method (SCS) at all the glucose
concentrations. This may be due to the higher total acid density and larger mesopore
formation facilitated in the hydrothermal treatment method. However, TOF values
calculated for HSCS samples are comparable with those of the SCS samples (Table
3). Further, the performances of HSCS materials are also comparable with those
reported for sulfonic acid modified silica catalysts (82.5% for Ar-SBA-15 and 79.0%
Pr-SBA-15) (Table 4.5). However, the performances of the catalysts are not directly
correlated with the amount of sulphur estimated by elemental analysis. This may be
due to the combined contribution of -COOH and phenolic - OH groups (in addition to
-SO3H) to the total acidity. This is in accordance with the results reported for the
sulfonated carbon catalysts.19
Further, the co-presence of the hydrophilic –COOH and
phenolic –OH groups in the HSCS materials of the present study may also play an
important role in promoting the activity of the catalyst by creating strong affinity
between the hydrophilic parts of the reactants with the catalyst. Thus the presence of
acidic SO3H groups along with hydrophilic groups (-COOH & -OH) present in
Chapter 4. Optimization of Acid Functionalized Carbon-Silica………..…… ……Silica preparation
Ph. D. Thesis of Mr. Devaki Nandan Page 122 CSIR-IIP
composite material of present study provides a beneficial factor for the development
of the catalytic process for solketal production, and the catalyst also exhibits constant
glycerol conversion up to the 4 reaction cycles (Table 4.6).
4.4 Conclusions
The synthesis of sulfonated carbon-silica-meso composite materials with
tuneable acidity and porosity are adopted for first time by applying simple one step
method of simultaneous carbonization and sulfonation. The simplicity involved in the
material synthesis using low cost glucose as a carbon source as well as structure
directing precursor makes the present method novel to those relevant works reported
in the prior art. The materials exhibited excellent catalytic activity in the acetalization
of acetone with a renewable feedstock, glycerol to produce 2,2-dimethyl-1,3-
dioxolane-4-methanol (solketal) thus provides an efficient heterogenous catalyst for
the value addition of the undesired bi-product glycerol obtained in the biodiesel
synthesis. The glycerol conversion and product selectivities achieved on these
Table 4.6 Recycling experiments on the HSCS1/2 catalyst for the synthesis of solketala
Run Glycerol conversion Total acid densityb (mmol/g)
1 82 2.25
2 80 2.20
3 81 2.19
4 79 2.15
a0.25 g of catalyst (5% of glycerol weight) was taken in a round bottom flask and 18.91g
of acetone and 5 g of glycerol with glycerol to acetone molar ratio 1:6 was added to it and
reflux at 70 0C for 30 min bacidity was determined by acid base titration.
Chapter 4. Optimization of Acid Functionalized Carbon-Silica………..…… ……Silica preparation
Ph. D. Thesis of Mr. Devaki Nandan Page 123 CSIR-IIP
materials are comparable to those reported for other sulfonated materials. Moreover,
the active mesoporous materials do not suffer from leaching problems and can be
efficiently reused in consecutive catalytic cycles. The synthesized SCS materials and
the mesoporous silica (MS) obtained by carbon removal through simple calcination of
SCS exhibit different porosity and can be used as catalysts and supports for vivid
catalytic applications.
4.5 References
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Chapter 5. Synthesis of Carbon Embedded MFe2O4…. ………………………Efficient Hydrogenation Catalysts
Chapter 5: Synthesis of Carbon Embedded MFe2O4 (M =
Ni, Zn and Co) Nano-particles as Efficient Hydrogenation
Catalysts
Effective interaction between precursors produces quality materials
Ph.D. Thesis of Mr. Devaki Nandan CSIR-IIP
Chapter 5. Synthesis of Carbon Embedded MFe2O4…. ………………………Efficient Hydrogenation Catalysts
Ph.D. Thesis of Mr. Devaki Nandan Page 127 CSIR-IIP
Chapter 5: Synthesis of Carbon Embedded MFe2O4 (M =
Ni, Zn and Co) Nano-particles as Efficient Hydrogenation
Catalysts
5.1 Introduction
Recently carbon materials are gaining importance as catalyst supports because of
their energy efficient and environment friendly synthesis process facilitated by simple
hydrothermal treatment of low-cost chemicals such as glucose. 1-5
This type of
synthesis process belongs to “green chemistry” because the reactant is safe and the
preparative process causes no contamination to the environment. Moreover, the
material also possesses the properties suitable for functionalization with acidic and
metal groups required for catalytic applications. According to the research findings on
the synthesis steps of carbon based materials, the carbon source first polymerize to
form small spheres or agglomerated particles which begin to carbonize to form multi
aromatic carbon sheets that eventually lead to the formation of well condensed inner
dense carbon matrix with outer layer of multi aromatic ring during the process of
hydrothermal synthesis and heat treatments.1, 6-9
The high temperature carbonization
treatments given during the process give the material thermal and chemical stabilities
to efficiently protect the metal spheres from being dissolved in protic environment as
the dense structure of the materials inhibit the hydrogen or hydroxyl ion to get in
contact with metal. Moreover, the outer multi carbon layer of the material can have
many functional groups, such as carboxylic, aldehyde, and hydroxyl groups, on their
surface suitable for establishing chemical interaction with the desired compounds
such as noble metal nano-particles (NPs) to obtain metal functionalized catalysts.10,11
From above advantages, many researchers have tried to attach metal spheres or metal
Chapter 5. Synthesis of Carbon Embedded MFe2O4…. ………………………Efficient Hydrogenation Catalysts
Ph.D. Thesis of Mr. Devaki Nandan Page 128 CSIR-IIP
nano-particle on to the carbon support.12-14
Wang et al. used oleic-acid-decorated
Fe3O4 NPs as the core of Fe3O4/carbon spheres.15
Zhang et al. reported the fabrication
of functional 1D magnetic NPs chains with thin carbon coatings by using urea as the
surfactant.16
However, the size uniformity and the thickness of carbon layer still need
to be better controlled and its application as catalyst support needs to be investigated.
In the present work, magnetically separable carbon supported MFe2O4 nano-
particles (MFe2O4 @C) where M = Ni2+
, Zn2+
and Co2+
have been successfully
synthesized by adopting a novel route of using environment-friendly phloroglucinol
as carbon source and levulinic acid possessing both carbonyl and carboxyl functional
groups as connecting agent between metal ions and the carbon source through
hydrothermal treatment followed by carbonization, where, the interaction of carboxyl
groups with the metal ions is believed to be responsible for the formation of MFe2O4
nano particles. The synthesized materials are explored for their catalytic application
in selective hydrogenation reactions.
The selective hydrogenation of organic molecules is one of the most important
chemical reactions for the synthesis of new compounds and the synthesis of effective
catalysts that can catalyze hydrogenation of arenes under milder conditions remains a
significant challenge.17
The reaction can be catalyzed homogeneously or
heterogeneously, but it is well recognized that the heterogeneous version is by far
more interesting from an industrial point of view,18
offering well-known benefits in
terms of waste reduction, easy separation of the catalysts and its recyclability.19
With
the aim of improving efficiencies, new catalysts and supports are being developed
continuously. Transition metals, such as Pd, Pt, Ru and Rh or Ni, both homogenous
and heterogeneous, are catalysts of choice for this reaction. However, in an effort to
develop a more sustainable approach, their cost, toxicity and potential depletion has
Chapter 5. Synthesis of Carbon Embedded MFe2O4…. ………………………Efficient Hydrogenation Catalysts
Ph.D. Thesis of Mr. Devaki Nandan Page 129 CSIR-IIP
fuelled the development of alternative hydrogenation catalysts. Iron, Cobalt and
Nickel complexes were shown to be active catalysts 20
for the hydrogenation of
olefins,21
and the selective hydrogenation of alkynes to alkenes. Recent developments
in nano materials provided efficient methods for catalyst development and the use of
iron in the form of suspendable nano particles for its applications in catalysis is
interesting as it also provides magnetic properties suitable for easy separation of the
catalyst from the reaction mixture. One of the challenging tasks in this regard is the
achieving stability of metal nano particles on the catalyst support. Stein et al.,22
have
overcame this limitation by stabilizing Fe NPs made by decomposition of Fe(CO)5 on
to graphene sheets. Although the resulting particles were active hydrogenation
catalysts, they were prone to oxidation in the presence of either oxygen or water
atmosphere prevail during the reaction.
The present method deals with the concept of simultaneous carbonization and
metal dispersion to synthesize MFe2O4 oxide nano-particles embedded carbon
support (MFe2O4@C) useful for the selective hydrogenation of double bond present
in cyclic hydrocarbons (non-aromatic) and side chains. The catalyst NiFe2O4@C
exhibits excellent activity in selective hydrogenation of styrene to achieve as high as
100% selectivity towards side chain hydrogenation to form ethyl benzene as well as
hydrogenation of cyclohexene to cyclohexane (75%). The materials also possess
stability in the protic environment of the solvent such as ethanol that makes the
method advantageous for catalytic applications. Compared to the reported prior art
catalysts, the as-synthesized catalyst of the present study exhibits higher or
comparable catalytic activity and better recyclability towards the reduction of styrene
and cyclohexene in the presence of protic solvent viz. ethanol.
Chapter 5. Synthesis of Carbon Embedded MFe2O4…. ………………………Efficient Hydrogenation Catalysts
Ph.D. Thesis of Mr. Devaki Nandan Page 130 CSIR-IIP
5.2 Experimental
5.2.1 Reagents and Chemicals
All the reagents were of analytical grade (Merck India Ltd.) and used without further
purification including phloroglucinol, glucose, Fe(NO3)3, Zn(NO3)2, Co(NO3)2 and
levulinic acid, while deionized water was used for preparing the solutions.
5.2.2 Synthesis of MFe2O4@C Materials
The MFe2O4 nanoparticles were prepared by the hydrothermal method. In a typical
synthesis procedure a certain amount of phloroglucinol was dissolved in water to
form a clear solution, followed by sequential addition of Fe(NO3)3 solution, bivalent
metal solution (NiCl2 or Zn(NO3)2 or Co(NO3)2) and levulinic acid. The mixture with
the molar ratio of 1 Fe(NO3)3: 1.05 phloroglucinol : 4.5 levulinic acid : 1.68 M salt
(NiCl2 or Zn(NO3)2 or Co(NO3)2) : 73 H2O was stirred vigorously for 60 minutes and
then sealed in a Teflon-lined stainless-steel autoclave (250 ml capacity). The
autoclave was heated and maintained at 170 °C for 48 h, and then allowed to cool to
room temperature. The black solid product obtained at the end of the synthesis was
then carbonised at 500 °C for 4 h under a nitrogen atmosphere, cooled down to room
temperature and washed several times with ample amount of water followed by
ethanol, which was finally dried at 60 °C for 6 h.
5.2.3 Application of Synthesized Materials for Selective Hydrogenation Reaction
The catalytic performance of all the synthesized materials has been studied towards
the hydrogenation of three types of reactants (scheme 5.1) namely (1) styrene, (2)
cyclohexene and (3) cyclohexanone. In a typical reaction procedure, 10 ml ethanol
was added to a mixture of 1 mol styrene/cyclohexene/cyclohexanone and 5 mol% of
Chapter 5. Synthesis of Carbon Embedded MFe2O4…. ………………………Efficient Hydrogenation Catalysts
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Scheme 5.1 Chemical structures of reactants and products.
catalyst and the whole mixture was transferred to a Parr reactor autoclave of 25 ml
volume capacity, sealed tightly and pressurised by hydrogen up to 40 bar. The
reaction was conducted at 80 °C for 24 h and the product obtained at the end of the
run was filtered and analysed by GC/GC-MS. The qualitative measurement of the
product was performed by GC-MS, while the quantitative analysis was performed
with GC results. The reaction product is analyzed using a GC equipped with the
DBwax column and the FID detector. After the completion of the reaction, the
catalyst was recovered from the reaction mixture via magnetic separation followed by
washing with hot water, ethanol, dried at 100 °C and reused for multiple cycles. The
recyclability of the as-synthesized catalyst was determined using the spent catalyst up
to 4 cycles. Further to see the effect on reaction kinetics the 4th time recycled catalyst
was used and the reaction product was analyzed at different time intervals. The
Chapter 5. Synthesis of Carbon Embedded MFe2O4…. ………………………Efficient Hydrogenation Catalysts
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reaction was also conducted homogeneously under the same reaction conditions so as
to check the activity of free metal ions where NiCl2 and Fe(NO3)3 salt solutions were
directly used as the source of Ni2+
and Fe3+
ions with the concentration of ions
equivalent to those in the heterogeneous NiFe2O4@C catalyst.
5.3 Results and Discussion
5.3.1 Scanning Electron Microscopy and Transmission Electron Microscopy and
High Resolution Microscopy
The morphology and structure of the materials were examined by field emission
scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM)
and high resolution TEM (HRTEM). The FE-SEM images of as synthesized materials
shown in Figure 5.1 reveal the difference in morphology of the particles, where, well-
defined and uniform size spherical particles of ~30 nm is observed for CoFe2O4@C
sample. The ZnFe2O4@C also exhibited similar size and morphology but the particles
are appeared as close agglomerates in this sample. On the other hand, the
NiFe2O4@C material exhibited compact agglomerated morphology without showing
any clear defined particles. The TEM images of NiFe2O4@C, ZnFe2O4@C and
CoFe2O4@C materials (Figure 5.2) clearly show the presence of metal oxide nano-
particles at carbon with a grain size range of 10–20 nm. The size of metal oxide nano-
particles (indicated with arrows in images) in case of NiFe2O4@C is smaller than that
of ZnFe2O4@C and CoFe2O4@C materials. Further, the HRTEM images of
NiFe2O4@C (Figure 5.3) reveal, well-resolved lattice fringes with an inter plane
distance of 0.252 nm (representing the spinel type of the lattice structure of MFe2O4)
arising from the (311) plane of MFe2O4.
Chapter 5. Synthesis of Carbon Embedded MFe2O4…. ………………………Efficient Hydrogenation Catalysts
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Figure 5.1 SEM images of MFe2O4 nano-particles@C.
Chapter 5. Synthesis of Carbon Embedded MFe2O4…. ………………………Efficient Hydrogenation Catalysts
Ph.D. Thesis of Mr. Devaki Nandan Page 134 CSIR-IIP
Figure 5.2 TEM images of MFe2O4 nano-particles@C.
Chapter 5. Synthesis of Carbon Embedded MFe2O4…. ………………………Efficient Hydrogenation Catalysts
Ph.D. Thesis of Mr. Devaki Nandan Page 135 CSIR-IIP
Figure 5.3 HRTEM images of MFe2O4 nano-particles@C.
Chapter 5. Synthesis of Carbon Embedded MFe2O4…. ………………………Efficient Hydrogenation Catalysts
Ph.D. Thesis of Mr. Devaki Nandan Page 136 CSIR-IIP
5.3.2. X-Ray Diffraction and Porosimetry
HRTEM images of MFe2O4 (Figure 5.3) revealed the well-resolved lattice fringes
with an inter plane distance of 0.252 nm (representing the spinel type of the lattice
structure of MFe2O4) arising from the (311) plane of MFe2O4@C materials, which are
consistent with the X-ray diffraction results (Figure 5.4A). The wide angle XRD
analysis (Figure 5.4A) revealed that the positions and relative intensities of the
diffraction peaks matched well with those of the standard MFe2O4. The peaks at 2θ
values at 18.50, 30.28, 35.76, 37.20, 43.72, 54.08 and 57.40 indexed to the (111),
(220), (311), (222), (400), (422) and (511) planes of a face-centered cubic M2+
iron
spinel phase respectively, which are consistent with the standard XRD data of the
MFe2O4 phase (JCPDS No. 10-325). If we compare the intensity of the NiFe2O4@C
it is sharp and intense than that of ZnFe2O4@C and CoFe2O4@C this may be due to
less carbon encapsulated (more carbon embedded) structure of this sample.23
The
XRD spectra of ZnFe2O4@C exhibited other peaks at 2θ 31.6, 34.4, 36.2 are indexed
to the (100), (002) and (101) planes of hexagonal ZnO wurtzite structure (as
Figure 5.4 (A) Wide angle XRD patterns of MFe2O4 nano-particles@C materials (B)
enlarged XRD of ZnFe2O4@C.
Chapter 5. Synthesis of Carbon Embedded MFe2O4…. ………………………Efficient Hydrogenation Catalysts
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impurity), (JCPDS data no. 36-1451) (Figure 5.4B)24-26
while such crystalline
impurities are not observed in other two samples i.e NiFe2O4@C and CoFe2O4@C.
The particle size of the materials is further supported by the average crystallite size of
the materials estimated from the full width at half maxima of the respective peaks at
2θ values of 29–60ο (in XRD), using Scherrer’s equation (Table 5.1). The particle
size measured by XRD further match with the size measured by TEM images of
NiFe2O4@C, ZnFe2O4@ and CoFe2O4@C materials as shown in figure 5.2.
The porous nature of the materials was confirmed by measurement of the
nitrogen adsorption–desorption isotherm (Figure 5.5) that represents the type-IV
isotherm with a hysteresis loop in the range of 0.7–1.0 P/P0, suggesting the capillary
condensation of the adsorbed gas in the narrow pores of the material (Figure 5.5).
Figure 5.5 N2 adsorption desorption isotherm and respective pore size distribution (inset) of
MFe2O4 nano-particles @ carbon. (A) NiFe2O4@C (B) ZnFe2O4@Cand (C) CoFe2O4@C.
Chapter 5. Synthesis of Carbon Embedded MFe2O4…. ………………………Efficient Hydrogenation Catalysts
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The pore size distribution of the corresponding sample measured by the Barrett–
Joyner–Halenda (BJH) method (Figure 5.5 inset) further reveals the hierarchical
nature of the porous MFe2O4@C sample where the presence of mesopores of
different diameter was observed to coexist. The BET surface area and total pore
volume measurements of the hierarchical porous NiFe2O4@C of the present study are
13 m2g
−1 , 0.12 cm
3g
−1which are almost similar to that of the single crystal magnetite
hollow spheres of Fe3O4 reported in the literature (13.5 m2g
−1 total pore volume is
0.21 cm3g
−1), while the surface area and the total pore volume of ZnFe2O4@C and
CoFe2O4@C are 27 m2g
−1, 0.17 cm
3g
−1and 39 m
2g
−1, 0.18 cm
3g
−1respectively show
that these materials are more porous than that of NiFe2O4@C.
5.3.3. FT-IR, EDX, CHNS and ICP-AES Investigation
The Fourier Transmission Infrared (FT-IR) spectra (Figure 5.6) of the NiFe2O4@C,
ZnFe2O4@C and CoFe2O4@C demonstrate the evidence for the formation of carbon
supported MFe2O4, where we can see the two bands -OH stretching and C=C in-plane
Table 5.1 Textural properties of synthesized materials.
Sample SABET a
m2g
-1
Vtot b
cm3g
-1
Vmi c
cm3g
-1
Vmes d
cm3 g
-1
D e
nm
Crystallite f
Size (nm)
NiFe2O4@C 13.2 0.12 0.05 0.07 27.6 36.24
ZnFe2O4@C 27.2 0.17 0.02 0.15 21.0 15.5
CoFe2O4@C
39.3 0.18 0.01 0.17 18.9 18.2
aBET surface area.
btotal pore volume taken from the volume of N2 adsorbed at P/P0 =
0.995. cmicropore volume calculated from t-plot.
dmesopore volume calculated by
Vtot-
Vmi. eBJH adsorption average pore diameter.
fcrystal size measured by Scherrer's equation
for the peak 2θ value 30-60ο.
Chapter 5. Synthesis of Carbon Embedded MFe2O4…. ………………………Efficient Hydrogenation Catalysts
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vibrations27
respectively. The band at 591-600 cm-1
could be ascribed to the typical
lattice absorption property of MFe2O4@C that confirms the existence of MFe2O4
structure.28
The elemental composition of the sample analyzed by EDX spectra (Figure
5.7) further confirms the presence of carbon, M2+
metal and iron metal in the
materials. The percentage of metal and carbon is given in Table 5.2, where the metal
percentage was determined by ICP and percentage of carbon was determined by EDX
and CHNS analysis. All the three samples exhibited the comparable carbon content of
23-25 wt.% and is in accordance with the weight of the carbon source and levulinic
acid taken in initial gel (taken similar in the synthesis mixture). The wt% of divalent
metal ions (Ni2+
, Zn2+
and Co2+
) is observed to be higher than that of the trivalent one
(Fe3+
) which is again in accordance with the weight of metal salts taken during the
synthesis.
Table 5.2 Elemental composition of synthesized materials.
Sample C (wt%) Fea
(wt%)
Nia
(wt%)
Zna
(wt%)
Co a
(wt%) EDX CHNS
NiFe2O4@Cb 37.02 24.25 21.08 38.70 0 0
NiFe2O4@Cc 35.05 23.15 20.70 36.00 0 0
ZnFe2O4@Cb 31.72 23.04 28.03 0 37.77 0
CoFe2O4@Cb 30.02 25.09 26.38 0 0 37.85
NiFe2O4@Cd - - 0 0 0 0
aMetal % determined by ICP-AES.
bFresh catalyst.
cCatalyst after 4
th cycle.
dICP-
AES analysis using hot filtration after reaction
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Figure 5.6 (A) FT-IR spectra of NiFe2O4@C nano-particles, (B) FT-IR spectra of
ZnFe2O4@C nano-particles and (C) FT-IR spectra of CoFe2O4@C nano-particles.
Figure 5.7 (A) EDX spectra of NiFe2O4@C nano-particles, (B) EDX spectra of ZnFe2O4@C
nano-particle and (C) EDX spectra of CoFe2O4@C nano-particles.
Chapter 5. Synthesis of Carbon Embedded MFe2O4…. ………………………Efficient Hydrogenation Catalysts
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5.3.4 Proposed Mechanism for the Formation of MFe2O4@C Materials
The formation of such a high quality nano-particles MFe2O4@C material obtained in
the present study can be explained by the schematic reaction path of reactants
facilitated during the synthesis (Scheme 5.2) which is proposed based on the XRD,
TEM and porosimetry properties of the material. It is known from the prior art that
the carboxylic group containing compounds are used for the stabilization of metal
nano-particles29,30
and carbonyl group containing compounds are used for the
formation of polymer by reacting with phloroglucinol.31,32
Using this information, the
novel concept of establishing the metal-carbon support interaction in the monomer
level itself is achieved in the present study, where, the levulinic acid possessing both
carboxyl and carbonyl groups is used to facilitate interaction with M2+
and Fe3+
metal
ions on one side and with the carbon source phloroglucinol on the other side
respectively. Scheme 5.2 shows the possible formation of metal ion interacted
polymer species through the reaction among various chemical ingredients when
treated under autogenous pressure conditions inside the autoclave at 170 οC. The
material obtained from the autoclave is allowed for heat treatment at 500 οC for 4 h to
facilitate the carbonization that eventually lead to the formation of well dispersed
metal nano particles on the carbon support. The advantage and novelty of the present
method is involved in the first step of achieving metal- carbon source interaction
before starting any carbonization of carbon source, which up on subsequent
carbonization forms the well dispersed metal particles on the carbon support. Here,
the carboxyl group interaction of the metal ions helps to control any agglomeration of
the metal ions during the hydrothermal and carbonization steps.
Chapter 5. Synthesis of Carbon Embedded MFe2O4…. ………………………Efficient Hydrogenation Catalysts
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Scheme 5.2 Schematic illustration of the formation of MFe2O4@C nano-particles.
5.3.5 Catalytic Performance of Materials for Hydrogenation Reaction
The catalytic performance of the all the materials synthesized in the present study
has been tested for the hydrogenation of styrene having double bond at side chain
while keeping the similar reaction conditions of 80 οC, 40 bar H2 pressure. In a
typical procedure the reaction is conducted by taking 5 mol% of the catalyst and 1
mol of styrene/cyclohexene in a high pressure autoclave reactor (Parr 4848) where
reaction mixture was left under stirring condition at 500 rpm for 24h. To see the
effect heterogeneous conditions a reaction was also conducted homogeneously at
same reaction condition by taking same metal ions (Ni and Fe) in the same ratio as
that of heterogeneous NiFe2O4@C catalyst (Table 5.3). Out of three catalysts
NiFe2O4@C gave highest styrene conversion (100%) while ZnFe2O4@C and
CoFe2O4@C gave 85% and 75% styrene conversion respectively. No conversion was
observed in homogeneous condition. A common thing observed with all three
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catalysts is the highest product selectivity (100%) towards ethyl benzene (table 5.3).
The NiFe2O4@C catalyst stands as the best among the three catalysts and is further
explored for the conversion of other reactants; 1. Cyclohexene, having double bond in
the cyclic ring and 2. Cyclohexanone, where the double bond position is between
carbon of the cyclic ring and oxygen. The material also exhibited promising catalytic
activity in cyclohexene hydrogenation, but the conversion is less (70%) compared to
that of styrene. Contrary to this, no noticeable conversion is observed in the
cyclohexanone hydrogenation reaction on this material at similar reaction conditions
(Table 5.4). Hence, it is interesting to see that the material exhibited different
activities towards the hydrogenation of three different reactants; excellent catalytic
activity in the selective hydrogenation of styrene to ethyl benzene (as high as 100%
conversion and 100% selectivity), moderate activity towards cyclohexene to
cyclohexane (~60%) while no activity for cyclohexanone hydrogenation. These
results reveal that the material is highly selective for the hydrogenation of side chain
Table 5.3 Hydrogenation of styrene over synthesized materials.a
Catalyst Conversion (%) Product Ethyl benzene selectivity (%)
NiFe2O4@C 100 Ethyl benzene 100
ZnFe2O4@C 85 Ethyl benzene 100
CoFe2O4@C 75 Ethyl benzene 100
Ni2+
Fe3+
ionsb 0 - -
aReaction Conditions: reaction temperature= 80
oC, H2 pressure = 40 bar, reactant = 1
mmol, catalyst = 5 mol%, reaction time = 24 h, bNi
2+ & Fe
3+ ions with same ratio as in
NiFe2O4@C.
Chapter 5. Synthesis of Carbon Embedded MFe2O4…. ………………………Efficient Hydrogenation Catalysts
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double bond, moderately active for isolated double bond in the cyclic rings but
ineffective for the hydrogenation of carbonyl groups. This observation clearly
emphasizes the selective hydrogenation functionality of the present catalyst system to
apply for the hydrogenation of side chain double bonds with high conversion and
selectivity. The reaction parameters such as time and pressure were varied to see the
effect on conversion and selectivity. Figure 5.8A shows the effect of pressure on the
conversion, where increase of reaction pressure enhanced the conversion of styrene;
at initial 10 bar pressure the styrene conversion was only 35 % which was increased
to almost 100% at 40 bar pressure. Similar trend in increased styrene conversion was
also observed with the increase of the reaction time (Figure 5.8B). The curve shows
three regions, an exponential increase in conversion up to 3 h, followed by linear
increase up to 24 h reaction time; while the conversion is levelled off up to the
studied period of 26 h. We have seen that the optimum conversion (100%) on the
catalyst was achieved after 24 h reaction time. At any level of conversion the catalyst
exhibited as high as 100 % selectivity to the ethyl benzene product. The linear
increase of conversion with reaction time may be due to initial inhibition in
interaction of the reactant with the active sites of the catalyst in presence of the
Table 5.4 NiFe2O4@C catalysed hydrogenation reactions
S. No Reactant Product Conversion(%) Selectivity(%)
1a Styrene Ethyl benzene 100 100
2a Cyclohexene Cyclohexane 70 100
3a Cyclohexanone Cyclohexanol 0 -
aReaction Conditions: reaction temperature= 80
oC, H2 pressure = 40 bar, reactant = 1
mmol, catalyst = 5 mol%, reaction time = 24 h
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Figure 5.8 (A) Effect of pressure on conversion and (B) effect of time on conversion at 80 0C
reaction temperature by fresh NiFe2O4@C (■) and 4th time recycled NiFe2O4@C (▼) as a
catalyst.
Chapter 5. Synthesis of Carbon Embedded MFe2O4…. ………………………Efficient Hydrogenation Catalysts
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moiety towards hydrogenation. As the reaction time progress, the interaction of
molecules with the catalyst will be facilitated due to the porous nature of carbon that
results in increase in conversion values.
5.3.6 Reusability of the Catalyst
The catalyst NiFe2O4@C displayed a high leaching resistance capability. Reuse of the
recovered catalyst in four consecutive runs did not lead to any significant decrease in
its catalytic activity in terms of its conversion, yield and selectivity. Recycling and
reusability of the catalyst were examined by introducing the used catalyst up to four
times. The catalyst exhibited the magnetic nature that allowed separating the catalyst
from the reaction mixture using the magnet (Figure 5.9). After each run the catalyst
was separated by magnet and washed by hot water followed by ethanol and dried at
100 oC. The catalyst was effective enough to give comparable conversions after each
cycle (Figure 5.10), that demonstrates no significant loss in the catalytic activity was
observed during recycle operation. Further, the used catalyst obtained after the fourth
cycle was studied for its performance with reaction time of up to 26 h and the
performance with time is compared with that of the fresh catalyst in Figure 5.8B. It is
interesting to see almost identical conversion patterns of both fresh and recycled
catalyst at all the reaction time values studied that confirms the intact of active sites in
the catalyst during recycle operation and proves the recyclability performance of the
catalyst. The ICP-AES results along with the carbon percent given in Table 5.2 shows
that no leaching of the metals as well as carbon occurred during the reaction that
further supports the intact of active sites in the catalyst The leaching test was
performed for Ni2+
and Fe3+
by ICP-AES analysis using hot infiltration after reaction,
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Figure 5.9 Photograph of magnetic separation of NiFe2O4 nano-particle @C.
where no Ni2+
or Fe3+
ions were present in the filtrate. We also observed that the
amount of Ni2+
and Fe3+
present in the spent catalyst after four cycles of reuse is the
same as that of the fresh catalyst as estimated by ICP-AES (Table 5.2). A reference
experiment was also conducted in the absence of the catalyst to see catalytic role of
NiFe2O4@C where no conversion was obtained. To see the effect heterogeneous
conditions a reaction was also conducted homogeneously at same reaction condition
by taking same metal ions (Ni and Fe) in the same ratio as that of heterogeneous
NiFe2O4@C catalyst (Table 5.3). No reaction was progressed on the catalyst at
homogenous conditions thus supports the catalytic role of NiFe2O4 active sites in the
heterogeneous catalyst.
By virtue of its higher conversion of the double bond containing hydrocarbons
to produce a side chain hydrogenated product with high selectivity, the catalyst has
potential applications in the dye industry, fine chemical synthesis and petrochemicals.
Chapter 5. Synthesis of Carbon Embedded MFe2O4…. ………………………Efficient Hydrogenation Catalysts
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Figure 5.10 Reusability of NiFe2O4@C catalyst.
5.4 Conclusions
In summary, highly crystalline, uniform size spinel of MFe2O4
nanoparticles@C was obtained in the present study through the sol–gel hydrothermal
synthesis method followed by carbonization, adopting a novel approach of
establishing an interaction between the carbon source and metal ions in the monomer
level itself. The levulinic acid possessing both carboxyl and carbonyl functional
groups used in the presentstudy might be responsible for facilitating interaction with
the carbon source on the one hand and the metal ions on the other hand so as to form
the carbon embedded metal nanoparticles. Further, the–COOH group in levulinic acid
might be responsible for the stabilization of the NiFe2O4 unit against agglomeration
during polymerization/carbonization reactions of phloroglucinol. The NiFe2O4@C
catalyst exhibiting well dispersed small size nanoparticles of∼10 to 20 nm obtained in
the present study provides a scope for the synthesis of other metal nanoparticle
supported catalytic systems by adopting this novel approach of using bi-functional
Chapter 5. Synthesis of Carbon Embedded MFe2O4…. ………………………Efficient Hydrogenation Catalysts
Ph.D. Thesis of Mr. Devaki Nandan Page 149 CSIR-IIP
levulinic acid as a binding molecule for establishing strong metal–support interaction.
Excellent activity in selective hydrogenation of styrene to ethyl benzene exhibited by
the present catalyst system envisions its scope for industrial applications through the
hydrogenation of various non-aromatic double bonds involved in chemicalsystems
related to fine chemicals and drug delivery.
5.5 References
1. X. Sun and Y. Li, Angew. Chem., Int. Ed., 2004, 43, 597.
2. R. D. Cakan, M. M. Titirici, M. Antonietti, G. Cui, J. Maier and Y. S. Hu,
Chem. Commun., 2008, 3759.
3. Q. Wang, H. Li, L. Chen and X. Huang, Carbon, 2001, 39, 2211.
4. X. Xiang, L. Bai and F. Li, AIChE J., 2010, 56, 2934.
5. X. Xiang, H. I. Hima, H. Wang and F. Li, Chem. Mater., 2008, 20, 1173.
6. Y. Meng, D. Gu, F. Zhang, Y. Shi, H. Yang, Z. Li, C. Yu, B. Tu and D. Zhao,
Angew. Chem., Int. Ed., 2005, 44, 7053.
7. J. Chen, N. Xia, T. Zhou, S. Tan, F. Jiang and D. Yuan, Int. J. Electrochem.
Sci., 2009, 4, 1063.
8. N. Liu, H. Song and X. Chen, J. Mater. Chem., 2011, 21, 5345.
9. W. Chaikittisilp, M. Hu, H. Wang, H. Huang, T. Fujita, K. C. W. Wu, L.
Chen, Y. Yamauchi and K. Ariga, Chem.Commun., 2012, 48, 7259.
10. S. Xuan, Y. J. Wang, J. C. Yu and K. C. Leung, Langmuir, 2009, 25, 11835.
11. H. Zhang, X. Zhong, J. Xu and H. Chen, Langmuir, 2008, 24, 13748.
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12. Y. Si, T. Ren, B. Ding, J. Yub and G. Sun, J. Mater. Chem., 2012, 22, 4619.
13. T. Ren, Y. Si, J. Yang, B. Ding, X. Yang, F. Hong and J. Yu, J. Mater. Chem.,
2012, 22, 15919.
14. Z. Zarnegar and J. Safari, RSC Adv., 2014, 4, 20932.
15. Z. Wang, H. Guo, Y. Yu and N. He, J. Magn. Magn. Mater., 2006, 302, 397.
16. Z. Zhang, H. Duan, S. Li and Y. Lin, Langmuir, 2010, 26, 6676.
17. M. J. Climent, A. Corma and S. Iborra, Chem. Rev., 2011, 111, 1072.
18. P. A. Chase, T. Jurca and D. W. Stephan, Chem. Commun., 2008, 1701.
19. P. A. Chase and D. W. Stephan, Angew. Chem., Int. Ed., 2008, 47, 7433.
20. S. C. Bart, E. Lobkovsky and P. J. Chirik, J. Am. Chem. Soc., 2004, 126,
13794.
21. E. Karaoğlu, U. Özel, C. Caner, A. Baykal, M. M. Summak and H.
Sözeri, Mater. Res. Bull., 2012, 47, 4316.
22. M. Stein, J. Wieland, P. Steurer, F. Toelle, R. Muelhaupt and B. Breit, Adv.
Synth. Catal., 2011, 353, 523.
23. J. Huo, H. Song and X. Chen, Carbon, 2004, 42, 3177.
24. S. C. Pillai, J. M. Kelly, R. Rameshc and D. E. McCormackad, J. Mater.
Chem. C, 2013, 1, 3268.
25. S. Sun, X. Yang, Y. Zhang, F. Zhang, J. Ding, J. Bao and C. Gao, Prog. Nat.
Sci.: Mater. Int., 2012, 22, 639.
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26. A. M. Díez-Pascual, C. Xu and R. Luque, J. Mater. Chem. B, 2014, 2, 3065.
27. M. Acik, G. Lee, C. Mattevi, M. Chhowalla, K. Cho and Y. J. Chabal, Nat.
Mater., 2010, 9, 840.
28. M. Fu, Q. Jiao and Y. Zhao, J. Mater. Chem. A, 2013, 1, 5517.
29. Y. Wang, J. F. Wong, X. Teng, X. Z. Lin and H. Yang, Nano Lett., 2003, 3,
1555.
30. P. R. Selvakannan, S. Mandal, S. Phadtare, R. Pasricha and M. Sastry,
Langmuir, 2003, 19, 3545.
31. R. T. Mayes, C. Tsouris, J. O. Kiggans Jr., S. M. Mahurin, D. W. DePaoli and
S. Dai, J. Mater. Chem., 2010, 20, 8674.
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Chapter 5. Synthesis of Carbon Embedded MFe2O4…. ………………………Efficient Hydrogenation Catalysts
Ph.D. Thesis of Mr. Devaki Nandan Page 152 CSIR-IIP
Chapter 6. Synthesis of Hierarchical ZSM-5 Using Glucose as ….. …..its Catalytic Application
Chapter 6: Synthesis of Hierarchical ZSM-5 Using Glucose
as Templating Precursor and its Catalytic Application
Cheaper template glucose produce hierarchical material upon steam assisted
crystallization
Ph.D. Thesis of Mr. Devaki Nandan CSIR-IIP
Chapter 6. Synthesis of Hierarchical ZSM-5 Using Glucose as ….. …..its Catalytic Application
Ph.D. Thesis of Mr. Devaki Nandan Page 153 CSIR-IIP
Chapter 6: Synthesis of Hierarchical ZSM-5 Using Glucose
as Templating Precursor and its Catalytic Application
6.1 Introduction
Zeolites with their inherent porous crystalline acidic nature possessing uniform
pore size and large internal surface area find wide range of applications in catalysis,
separation and ion-exchange.1-3
Especially, the medium pore ZSM-5 zeolite attracted
much attention due to its shape-selective features responsible for its excellent
performance in the selective organic transformations. The narrow pores of this zeolite
exhibiting linear selectivity provide a special feature for the synthesis of para-xylene
from ortho- and meta-xylenes which is considered as a milestone in zeolite and
heterogeneous catalysis research fields. However, an obvious shortcoming of zeolite
materials originates from their intrinsic micro pores that strongly inhibit the diffusion
of bulky reactants and products, which prevents their wide use in fine chemical and
petrochemical processing. Al-containing mesoporous molecular sieves with large and
high specific surface could be the catalysts for the conversion of bulky reactants.4-6
But, these materials suffer from poor thermal and hydrothermal stability due to the
thin and amorphous nature of their walls. Therefore, the preparation of hierarchical
pore zeolite molecular sieves possessing the positive aspects of both micro-pores
(high activity and stability) and meso pores (larger pore size for accommodating
bulky molecules) has become the hot point of research recently. The most widely
used method to prepare hierarchical pore zeolite is by adopting special chemicals as
templates including hard and supramolecular structured compounds. Jacobsen et al.7
did pioneering work in the hard templating method and successfully synthesized
Chapter 6. Synthesis of Hierarchical ZSM-5 Using Glucose as ….. …..its Catalytic Application
Ph.D. Thesis of Mr. Devaki Nandan Page 154 CSIR-IIP
mesopore zeolites using carbon materials such carbon nano-tubes. The three-
dimensionally ordered mesoporous (3DOM) carbon materials are also used by other
researchers for the synthesis of mesoporous zeolite materials.8 Nevertheless, the
templates used in these methods are very costly. Later carbon aero gels9 and ordered
mesoporous carbons10,11
are also used as templates to prepare hierarchical zeolite, but
the preparation process of this carbon template itself is complicated and requires high
temperature and inert gas atmosphere during carbonization. In supra-molecular
templating method, the templates used are mainly Cetyltrimethylammoniumbromide
(CTABr),12
poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock
copolymer (P123)13
, and organosilane14
agents but they are also expensive. Recently,
through the combination of conventional soft templates such as TEA, copolymer
Pluronic F127, organosilane and steam-assisted crystallization (SAC) process,
hierarchically structured c-TUD-1, TS-1 and ZSM-5 zeolites15
have been facilely
produced, but use of these templates makes the process costly. Very recently,
monosaccharide's such as, glucose and disaccharides such as sucrose etc. are
identified as cheaper yet potential precursor for meso pore structure-directing agent.
Kustova et al.,16
synthesized zeolite single crystals with controlled mesoporosity by in
situ sugar decomposition for templating of hierarchical zeolites which is a three step
process where they synthesized first silica carbon composite in inert atmosphere and
used this composite material as a template which upon crystallization and calcination
yields Na-ZSM-5. The material was further treated with ammonium nitrate to obtain
NH4-ZSM-5 and the high temperature decompositions of which finally yields H-
ZSM-5. Ma et al.,17
synthesized mesoporous ZSM-5 where a precursor of ZSM-5 is
first prepared by sequential reaction between aluminium sulphate, solution,
Tetrapropylammonium hydroxide and Tetraethyl orthosilicate in a specific manner.
Chapter 6. Synthesis of Hierarchical ZSM-5 Using Glucose as ….. …..its Catalytic Application
Ph.D. Thesis of Mr. Devaki Nandan Page 155 CSIR-IIP
The resultant ZSM-5 precursor was added to the aqueous solution of glucose
followed by its heating to the crystallization temperature. The final solid product
obtained is calcined to remove the organic template, followed by ion exchange with
NH4NO3 and calcinations treatments so as to yield H-ZSM-5. Similar method was
also reported with difference of using starch derived bread instead of glucose for the
synthesis of the hierarchical ZSM-518,
Wang et al., 19,20
synthesized hierarchical TS-1
by using sucrose as meso macro template in presence of isopropyl alcohol where they
have used high cost ethylendiamine as crystallising agent. In present study, the
mesoporous silica have been successfully synthesized by using glucose as template
precursor in acidic medium. However, the same method is not applicable for the
synthesis of mesoporous ZSM-5 due to the fact that the metal to metal (silicon and
aluminium) bond formation is difficult to occur in acidic medium to yield any
crystalline material.
A novel method has been adopted in present study for the successful synthesis
of the hierarchical ZSM-5 zeolite material using environmentally benign glucose in
basic medium created by the addition of low cost aqueous ammonium hydroxide,
where the pore size pattern of the synthesized material is significantly influenced by
the concentration of glucose in the synthetic mixture. The present work gains
advantage over the existing methods as it uses a simple, low cost, non-surfactant
common chemical ‘‘glucose’’ as a template precursor that spontaneously get
converted to hard template during partial carbonization by drying of synthesis gel at
170 oC in air. Further, the use of ammonium hydroxide as alkaline agent instead of
sodium hydroxide makes the process simple to give proton form of ZSM-5 directly
and avoids the additional step of ion-exchange of sodium with ammonium ion. The
ammonium ZSM-5 to acidic ZSM-5 was formed during calcination, where at higher
Chapter 6. Synthesis of Hierarchical ZSM-5 Using Glucose as ….. …..its Catalytic Application
Ph.D. Thesis of Mr. Devaki Nandan Page 156 CSIR-IIP
temperature ammonium gas was escape out to leave H-ZSM-5. This is the first of its
kind to synthesize crystalline hierarchical aluminosilicate, MFI type material from
glucose and ammonium hydroxide medium to the best of our knowledge. The
catalytic performance of hierarchical ZSM-5 towards the bulky molecular reaction
was studied by choosing the alkylation of phenol with tertiary butanol.
6.2 Experimental
6.2.1 Reagents and Chemicals
Tetraethyl ortho silicate (TEOS), ammonia solution 25%,
tetrapropylammonium bromide (TPABr), phenol, tertiary butanol and aluminium
nitrate were purched from Merck while glucose was purchased from Rankem, The
reference ZSM-5 sample is obtained from Sud-Chemie India Ltd.
6.2.2 Synthesis of Hierarchical ZSM-5 Materials
As depicted in scheme 6.1, the typical synthesis procedure involves the drop by drop
admixing of Tetrapropylammonium bromide (TPABr) solution, Tetraethyl
orthosilicate (TEOS) , Aluminium nitrate solution and Glucose solution with the
molar ratio of TPABr : 5.2 TEOS : 0.215 aluminium nitrate : 2.4 to 4.9 glucose : 60
water. The resultant gel is treated at 170 oC in air and the dry gel obtained from the
mixture is allowed for steam assisted crystallization in a specially designed autoclave
equipped with porous metallic boat for holding the dry gel which is allowed to be in
contact with the steam produced from the bottom of the autoclave during heat
treatment (scheme 6.1). In a typical synthesis procedure 12.5 g tetrapropylammonium
bromide with required amount of glucose and water is added to TEOS followed by
the addition of 3.75 g of aluminium nitrate solution (in 5 g water). For studying the
Chapter 6. Synthesis of Hierarchical ZSM-5 Using Glucose as ….. …..its Catalytic Application
Ph.D. Thesis of Mr. Devaki Nandan Page 157 CSIR-IIP
effect of template precursor (glucose) the synthesis is conducted by varying the
glucose to TEOS weight ratio in the initial gel mixture from 0.40 to 0.64. The
resultant solution was dried in a water bath by treating at 80 oC for 2 h, and the
resulting viscous gel was further heated at 170 oC for 28 h to obtain the dry gel
(brown in colour). Finally, the dry gel (solid phase), along with a mixture of aqueous
ammonia (25%) and deionized water containing aqueous phase were transferred into
a specially designed autoclave, in which the solid phase was separated from the
aqueous phase. The crystallization was carried out at 170 oC for 6 days, where the
steam obtained from the aqueous phase comes in contact with the upper solid phase to
facilitate the crystallization process of the zeolite. At the end of the treatment, the
black colour solid product obtained was collected by filtration, washed with deionized
water, dried at 100 oC and calcined at 650℃ for 10 h to remove the template. The
final materials obtained in the synthesis are denoted by MZ0.40, MZ0.48 and MZ0.64
respectively, where the suffix indicates the wt. ratio of glucose to TEOS.
Scheme 6.1 Synthesis route of hierarchical ZSM-5 zeolite.
Chapter 6. Synthesis of Hierarchical ZSM-5 Using Glucose as ….. …..its Catalytic Application
Ph.D. Thesis of Mr. Devaki Nandan Page 158 CSIR-IIP
6.2.3. Application of Materials for Tertiary Butylation of Phenol
The catalyst performance studies of the materials have been conducted in the present
work towards the alkylation of Phenol. In a typical reaction procedure, 1 mol of
phenol was added to a 2.5 mol of tertiary butyl alcohol and 5 mol% of catalyst. The
whole mixture was transferred in to a 25 ml volume capacity Parr reactor autoclave,
sealed tightly and pressurised by N2 up to 2 bar. The reaction was conducted at 150
oC for 7h and the product obtained at the end of the run was filtered and analysed by
GC equipped with the DB wax column and FID detector.
6.3 Results and Discussion
6.3.1 Crystallinity, Porosity and Acidic Properties of the Synthesised Materials
The SEM images of the samples shown in Figure 6.1 indicate the formation of
uniform crystals in case of MZ0.40, when compared to those of MZO.48 and
MZ0.64. This can be ascribed to the variation in the concentration of templating
precursor, glucose taken in the synthesis gel. The non-uniform distribution of
templating precursor resulted at excess glucose concentration may be the reason for
the formation of non uniform semi-crystalline ZSM-5 materials. The powder X-ray
diffraction (XRD) patterns of the samples are given in Figure 6.2, where a standard
ZSM-5 sample of SAR is also taken for comparison purpose. All the three
synthesized materials depict the characteristic diffraction peaks occurred at 2θ of 8.0,
8.9, 23.2, 24 and 24.5 representing the ZSM-5 framework structure without any
crystalline impurity phases. The crystallite size of the materials was estimated from
full width at half maximum of the respective peaks between 2θ values, 7-10 using
Scherrer's equation and the average of the crystallite size is given in Table 6.1. The
data indicate the comparable crystal size of the materials synthesized in this study
Chapter 6. Synthesis of Hierarchical ZSM-5 Using Glucose as ….. …..its Catalytic Application
Ph.D. Thesis of Mr. Devaki Nandan Page 159 CSIR-IIP
Figure 6.1 SEM images of synthesized materials.
Chapter 6. Synthesis of Hierarchical ZSM-5 Using Glucose as ….. …..its Catalytic Application
Ph.D. Thesis of Mr. Devaki Nandan Page 160 CSIR-IIP
Figure 6.2 Wide angle XRD patterns of synthesized materials
Table 6.1 Textural properties of the synthesized materials.
Sample SABET a
(m2g
-1)
SAmi b
(m2g
-1)
SAme c
(m2g
-1)
Vtot d
(cm3g
-1)
Vmi e
(cm3g
-1)
Vme/ma f
(cm3 g
-1)
D g
(nm)
Sizeh
(nm)
ZSM-5 294 207 87 0.18 0.08 0.10 2.2 50.3
MZ0.40
305 113 192 0.18 0.05 0.13 2.3 51.7
MZ0.48
107 25 82 0.18 0.01 0.17 6.7 57.0
MZ0.64
128 42 86 0.23 0.01 0.22 7.2 47.4
aBET surface area.
bmicropore surface area calculated from t-plot.
cmesopore surface area
were calculated as (a-b). d
total pore volume taken from the volume of N2 adsorbed at P/P0 =
0.995. emicropore volume calculated from t-plot.
fmesopore /macropore volume calculated
by Vtot-Vmi.
gBJH adsorption average pore diameter.
haverage crystal size measured by
Scherrer's equation for the peaks between 2θ value 7ο-10
ο
Chapter 6. Synthesis of Hierarchical ZSM-5 Using Glucose as ….. …..its Catalytic Application
Ph.D. Thesis of Mr. Devaki Nandan Page 161 CSIR-IIP
with that of the conventional ZSM-5 zeolite. The small angle X-ray scattering
(SAXS) patterns of the as-synthesized samples (Figure 6.3) suggest the presence of
larger mesopores in the materials,21
which is indeed confirmed by N2 adsorption-
desorption isotherm curves of the corresponding samples (Figure 6.4A). All the
samples exhibited the type IV isotherm with H1 type hysteresis loop which usually
observed for the larger mesopores. The sharp uptake in nitrogen adsorption at relative
pressures of 0.6–0.9 P/P0 reveals the capillary condensation of the gas inside the
mesopores. A steep increase at relative pressure P/P0 <0.02 and a significant
adsorption at high relative pressure P/P0 0.9-1.0, indicates the co-existence of intrinsic
micro, meso and macropores in all three samples. However, the concentration of
glucose in the initial synthetic gel was observed to influence the porosity of the
samples significantly. At lower glucose concentration, the isotherm exhibited the
formation of more micropores (pressure range of P/P0 < 0.02), while at higher glucose
concentration dramatically shifted the porosity in to meso/macropores (relative
Figure 6.3 Low angle XRD patterns of synthesized samples
Chapter 6. Synthesis of Hierarchical ZSM-5 Using Glucose as ….. …..its Catalytic Application
Ph.D. Thesis of Mr. Devaki Nandan Page 162 CSIR-IIP
Figure 6.4 A: N2 adsorption-desorption isotherms of synthesized materials, B: Pore
size distribution of the respective samples measured by BJH method.
Chapter 6. Synthesis of Hierarchical ZSM-5 Using Glucose as ….. …..its Catalytic Application
Ph.D. Thesis of Mr. Devaki Nandan Page 163 CSIR-IIP
pressure range of 0.6–0.9 P/P0). This phenomenon of enhanced mesopores/macropore
formation at higher glucose concentrations is further reflected in the pore size
distribution patterns of the materials (Figure 6.4B). All the materials exhibited the
hierarchical pore size distribution patterns with significant contribution of mesopores
as well as macropores (Figure 6.4B). However, the population of such hierarchical
pores is dramatically increased in the higher glucose used samples and the increase is
following the glucose concentration. Thus the increasing order of hierarchical
porosity is observed as follows; ZSM-5< MZ0.40 < MZ0.48 < MZ0.64. The finding
of increased hierarchical pore size distribution with glucose concentration can be
understood from the XRD results, where the increase in glucose concentration is
observed to increase the amorphous nature of the material (lower crystallinity). This
is to say that the semi crystalline ZSM-5 material containing more amount of
amorphous material is forming at higher glucose concentration and the presence of
such amorphous material is contributing to the formation of meso and macropores.
Such material with lower micropores and high amounts of meso/macropores is
expected to give lower surface area, which is indeed observed in the samples (Table
6.1). But, it is important to note that the total pore volume as well as
mesopores/macropore volume is increased in the higher glucose based synthesized
samples. This has resulted in the overall increase in the average pore diameter of the
samples with glucose concentration. The BJH adsorption average pore diameter of the
corresponding samples are 2.2, 2.3, 6.7 and 7.2 nm further suggests that increase of
glucose concentration leads to shift the mean pore diameter to higher value. Here
glucose undergoes dehydration and partial carbonization to form templating
carbonaceous species during the heat treatment of the gel at 170 oC which is
responsible for the creation of meso/macro pores in the final material up on steam
Chapter 6. Synthesis of Hierarchical ZSM-5 Using Glucose as ….. …..its Catalytic Application
Ph.D. Thesis of Mr. Devaki Nandan Page 164 CSIR-IIP
assisted crystallization. The formation of such meso/macropores is increased with
increased concentration of glucose. Overall, the increased formation of
meso/macropores with glucose concentration clearly envisions the meso/macro pore
directing role of glucose precursor.
The acidity patterns of the samples measured by TPD (Figure 6.5) also
followed the crystallinity trends of the samples. All the samples exhibited a two peak
pattern with desorption peaks at ~ 100 oC and ~350
oC representing the weak and
strong
Figure 6.5 TPD spectra of synthesised and reference materials.
acidity respectively. The acidity patterns of a reference ZSM-5 sample (Si/Al=15)
also given for comparison that envisions the acidity of all the three samples (Si/Al
Chapter 6. Synthesis of Hierarchical ZSM-5 Using Glucose as ….. …..its Catalytic Application
Ph.D. Thesis of Mr. Devaki Nandan Page 165 CSIR-IIP
=60) of the present study is less (less number of acid sites) compared to the reference
sample, following the aluminium content. Among the three ZSM-5 samples
synthesized the present study, the acidity is decreased with increasing glucose
concentration. This is in accordance with the XRD and porosity patterns, as the
increased amorphous nature of the material is expected to give low acidity (less
number of strong acid sites) to the ZSM-5 samples. The results together summarize
the role of glucose as meso-macro pore directing agent and the partially crystalline
hierarchical ZSM-5 obtained at higher glucose loadings exhibit moderate acidity
along with high amount of meso/macropores. With the higher pore volume and larger
space in mesopores, the samples are expected to exhibit potential catalytic
applications in bulky molecular reactions such as tertiary butylation of phenol.
6.3.2 Catalytic Performance of Materials for Tertiary Butylation of Phenol
The tertiary butylation of phenol is catalyzed by conventional homogeneous acid
catalysts in liquid phase at lower reaction temperatures, but the acid contamination
and difficulty involved in separation of the product (also adds to cost ) limits their
use. Recently solid acid catalysts are applying for solvent-free liquid phase reactions
for low cost and environment-friendly process, where the easy separation of catalysts
from the reaction system makes it suitable for industrial applications.22
In this regard,
hierarchical ZSM-5 samples are observed to exhibit excellent catalytic properties
especially in terms of di-alkylated product. The hierarchical mesoporous ZSM-5
samples of the present study possessing meso/macroporosity along with its zeolitic
microporosity are also expected to exhibit promising catalytic activity towards this
bulky reaction. In the present study we would like to explore the effect of glucose-
dependent meso/macroporosity created in the ZSM-5 samples on the conversion and
product selectivity towards the tertiary butylation of phenol. All the three hierarchical
Chapter 6. Synthesis of Hierarchical ZSM-5 Using Glucose as ….. …..its Catalytic Application
Ph.D. Thesis of Mr. Devaki Nandan Page 166 CSIR-IIP
ZSM-5 samples exhibited higher conversions (34-46%) when compared to the mere
microporous ZSM-5 zeolite (Table 2). The lower conversion of microporous ZSM-5
obtained in the reaction in spite of its higher acidity (Figure 6.5) clearly suggests the
importance of meso/macropores for this reaction and the lack of such porosity in the
standard ZSM-5 sample may be responsible for its lower activity. The catalytic
performance of the three hierarchical mesoporous ZSM-5 samples also followed the
porosity trend, where, the higher meso/macrporous material (MZ0.64) exhibited
higher conversion (44%) and relatively higher 4-TBP selectivity (81%). This sample
also produced highest di-alkylated product (2,4-DTBP).
Table 6.2 Tert-Butylation of phenol over hierarchical ZSM-5 samplesa
Catalysts Conversion of phenol
(mol% )
Selectivity of product (% )
2-TBP 4-TBP 2,4-DTBP
MZ0.40 34 38.2 57.3 4.5
MZ0.48 46.6 11.1 81.5 5.4
MZ0.64 44 10.6 80.9 8.5
ZSM-5 13.7 63.5 32.84 Nil
aCatalyst: 0.5 g, reaction temperature 150
oC, pressure 2 bar N2 ; reaction time 7h; Phenol:
TBA 1 : 2.5 (molar ratio).
Chapter 6. Synthesis of Hierarchical ZSM-5 Using Glucose as ….. …..its Catalytic Application
Ph.D. Thesis of Mr. Devaki Nandan Page 167 CSIR-IIP
6.4 Conclusions
In summary, the hierarchical ZSM-5 zeolite samples have been successfully
synthesized by using the low-cost template precursor glucose in basic medium that
can directly get converted to hard template during heat treatment of the gel to give
glucose-dependent porosity patterns in the samples. This method also provides scope
in using other kinds of sugars as template precursors for the synthesis hierarchical
materials. The synthesis method provides an economical path for the production of
hierarchical aluminosilicates with tailored meso/macroporosity (controlled by
glucose) for various industrial applications and could be extended for the synthesis of
other types of zeolites. The materials possessing well-connected network of
micro/meso/macropores can be source for the variety of bulky molecular reactions
and better replacement for conventional ZSM-5. The materials indeed exhibited
improved catalytic performance in tertiary butylation of phenol as a result of
overcoming the diffusion limitation of the reactants.
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2010, 46, 4994; J. Zhou, Z. Hua, Z. Liu, W. Wu, Y. Zhu and J. Shi,
ACS Catal., 2011, 1, 287. (b) J. Zhou, Z. Hua, J. Shi, Q. He, L. Guo and M.
Ruan, Chem.–Eur. J., 2009, 15, 12949.
16. M. Kustova, K. Egeblad, K. Zhu, and C. H. Christensen, Chem. Mat.,
2007, 19, 2915.
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17. Y. Ma, Jing Hu, L. Jia, Z. Li, Q. Kan and Shujie Wu, Mat. Res.
Bull., 2013, 48, 1881.
18. L. Wang1, C. Yin, Z. Shan, S. Liu, Y. Du and F. Xiao, Colloids and
Surfaces A: Physicochem. Eng. Aspects, 2009, 340, 126.
19. W. Wang, G. Li, L. Liu, Y. Chen, Microporous Mesoporous Mater., 2013,
179, 165.
20. X. Wang, G. Li, W. Wang, C. Jin and Y. Chen, Microporous Mesoporous
Mater, 2011, 142, 494.
21. Z. Niu, S. Kabisatpathy, J. He, L.A. Lee, J. Rong, L. Yang, G. Sikha, B. N.
Popov, T.S. Emrick, T. P. Russell, Q. Wang, Nano Res., 2009, 2, 474.
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Ph.D. Thesis of Mr. Devaki Nandan Page 170 CSIR-IIP
Chapter 7 Concluding Remarks and Future Prospects
Chapter 7: Concluding Remarks and Future Prospects
Ph. D. Thesis of Mr. Devaki Nandan CSIR-IIP
Chapter 7. Concluding Remarks and Future Prospects
Ph.D. Thesis of Mr. Devaki Nandan Page 171 CSIR-IIP
Chapter 7: Concluding Remarks and Future Prospects
Porous carbon composites and metal oxides of infinite network can be functionalized
by acid or metal ions for catalytic application. The ion–clusters connected with
hydrophobic carbon moiety or zeolite framework is observed to be subject in an
exponentially emerging chemical and material research field owing to its aesthetic
structural versatility as well as modularity for a wide spectrum of applications ranging
from adsorption, separation and catalysis to refinery, bio-oil, magnetism and
biomedical purposes. Precise designing strategies for acid functionalized porous
carbon composite, metal supported nano-particles and hierarchical zeolitic metal
oxides by using low cost carbon source such as petroleum waste, glucose, levulinic
acid and phloroglucinol or structure directing agent are the key factors for
development of cost effective synthetic protocols.
This Ph.D. thesis comprises of the research focused on the development of new 1)
porous carbon composites possessing acidity and magnetic properties and 2)
hierarchical porous zeolites having diverse structural features enriching the priori
information useful towards the ‘designing’ of novel materials. Some of the acid
functionalized, and metal functionalized porous carbon composites and hierarchical
metal oxides are synthesized, characterized and examined for their acidic, magnetic
and catalytic activity. Notable emphasize on the preparation of acid functionalized
porous carbon, magnetically separable carbon composite and hierarchical metal oxide
has been given by using low cost precursors. Efforts have also been made towards
the development of energy efficient catalytic applications such as alkylation of
phenol, value addition of glycerol and hydrogenation. The prime results described in
Chapter 7. Concluding Remarks and Future Prospects
Ph.D. Thesis of Mr. Devaki Nandan Page 172 CSIR-IIP
each chapter and their relevance to the practical applications is briefly summarized as
follows.
7.1 Facile synthesis of sulfonated carbon, carbon-silica-meso composite and
mesoporous silica
The simultaneous carbonization and sulfonation of low cost carbon
precursors (coal tar) has been adopted to synthesize thermally stable acid
functionalized nanoporous carbon without using any costly structure
directing agent.
Use of renewable glucose as carbon source as well as templating precursor
was successfully demonstrated for the preparation of sulfonated carbon-
silica meso composite (SCS).
The acid functionalized carbon silica composite also can be used for the
synthesis of mesoporous silica by simple calcination and the resultant
mesoporous silica has wide application depends on metal functionalization.
7.2 Optimization of carbon silica composite structure and their catalytic
applications
Glucose as a carbon source and structure directing precursor has been used
for the synthesis of various carbon silica composite materials.
Tailorble porosity of composite materials has been achieved by varying the
glucose concentration in initial synthesis mixture
The synthesized materials have been successfully used for the value
addition of glycerol for the solketal production
Chapter 7. Concluding Remarks and Future Prospects
Ph.D. Thesis of Mr. Devaki Nandan Page 173 CSIR-IIP
7.3 Synthesis of carbon embedded MFe2O4 (M = Ni, Zn and Co) nano-particles
as efficient hydrogenation catalysts
A novel concept of using levulinic acid having both carboxylic
(for interaction with M2+
and Fe 3+) and carbonyl groups (for
interaction with phloroglucinol) has been successfully adopted for the
synthesis of carbon embedded metal nano-particles.
Interaction of levulinic acid restricts the agglomeration of metal nano-
particle so that their size remains smaller.
Simultaneous polymerization then carbonization of the precursors at higher
temperature gives stable carbon supported nano-particle (no leaching and
oxidation in protic solvent viz. ethanol).
Both the chemicals levulinic acid and phloroglucinol are cheaper,
renewable, non-hazardous which can avoid use of high cost
surfactant for stabilizing nanoparticles.
The synthesized NiFe2O4@C materials have been identified to be excellent
side chain hydrogenation catalysts (selective hydrogenation) towards
model reaction of styrene hydrogenations where as high as 100%
conversion of styrene to produce 100% ethyl benzene was obtained. This
shows potential side chain selective hydrogenation ability of the new
compound NiFe2O4@C.
7.4 Synthesis of hierarchical ZSM-5 using glucose as templating precursor and
its application
Chapter 7. Concluding Remarks and Future Prospects
Ph.D. Thesis of Mr. Devaki Nandan Page 174 CSIR-IIP
A novel concept of using low cost glucose as a templating precursor
has been realized to get hierarchical ZSM-5.
In the present study glucose was used as a cheaper, renewable, non-
hazardous which can avoid use of high cost surfactant and organosilane.
Aqueous ammonia instead of NaOH as alkali source has been used
during crystallization for the direct production of protonic zeolite that
avoids the otherwise required additional steps of ion-exchange with
ammonia and calcination of the final material.
The other important advantage of the present method lies in obtains desired
porosity by simple method of varying glucose concentration for fine tuning
the pore size.
Overall the present research work addresses the facile synthesis of various types of
materials adopting novel concepts for successful production of the materials such as
acid functionalized nanoporous carbon, acid functionalized carbon silica composite,
hierarchical mesoporous silica, magnetically separable carbon embedded metal nano-
particle (NiFe2O4@C, ZnFe2O4@C and CoFe2O4@C) and hierarchical ZSM-5 to
have potential catalytic applications. Each category of material has been readily
applied for an industrially important reaction in addition to their in depth contribution
to the basic understanding of the chemistry. Some of the reactions studied in this
regard are bulky molecular aryl alkylation reaction, value addition of glycerol
towards solketal synthesis and selective hydrogenation of alkyl aryls. The studies
indicated the potential applicability of the synthesized materials with their ready
suitability for additional functionalization with other metals for catalytic
transformations but the complete study of the spectrum of reactions that can actually
Chapter 7. Concluding Remarks and Future Prospects
Ph.D. Thesis of Mr. Devaki Nandan Page 175 CSIR-IIP
catalyzed by the synthesized materials is beyond the scope of this study. However,
the each type of reaction studied in the present work represents a class of molecular
conversions that can be explored by using the materials of the present study and has a
wide scope for process development in the important areas of catalysis, adsorption,
drug delivery, magnetic separation etc.
7.5 Papers Published in International Journals
1. Facile single step synthesis of an acid functionalized nano porous carbon
composite as an efficient catalyst for tertiary butylation of phenol, Devaki
Nandan and Nagabhatla Viswanadham, RSC Adv., 2014, 4, 57223. (Impact
Factor 3.708).
2. Synthesis of carbon embedded MFe2O4 (M = Ni, Zn and Co) nano-particles
as efficient hydrogenation catalysts, Devaki Nandan, Peta Sreenivasulu,
Nagabhatla Viswanadham , Ken Chiang and Jarrod Newnham, Dalton
Transactions, 2014, 43, 12077. (Impact Factor 4.02)
3. Synthesis of hierarchical ZSM-5 using glucose as templating precursor
and its application, Devaki Nandan, Sandeep K. Saxena and Nagabhatla
Viswanadham, J. Mater. Chem. A, 2014, 2 , 1054. (Impact Factor NA)
4. Acid functionalized carbon–silica composite and its application for solketal
production, Devaki Nandan, Peta Sreenivasulu, L.N. Sivakumar Konathala,
Manoj Kumar, Nagabhatla V iswanadham, Microporous and Mesoporous
Materials, 2013, 179, 182 (Impact Factor 3.365)
5. Facile synthesis of a sulfonated carbon silica-meso composite and
mesoporous silica, Devaki Nandan, Peta Sreenivasulu, Sandeep K. Saxena
Chapter 7. Concluding Remarks and Future Prospects
Ph.D. Thesis of Mr. Devaki Nandan Page 176 CSIR-IIP
and Nagabhatla Viswanadham, Chem. Commun., 2011, 47, 11537 (Impact
Factor 6.7)
6. Synthesis and catalytic applications of hierarchical mesoporous
AlPO4/ZnAlPO4 for direct hydroxylation of benzene to phenol using hydrogen
peroxide, Peta Sreenivasulu, Devaki Nandan, Manoj Kumar and Nagabhatla
Viswanadham, J. Mater. Chem. A, 2013, 1, 3268 (Impact Factor 6.101)
7. Room temperature synthesis of ZnAlPO4 nanoparticles and their catalytic
applications, Peta Sreenivasulu, Devaki Nandan, B. Sreedhar and Nagabhatla
Viswanadham, RSC Advances, 2013, 3, 13651 (Impact Factor 3.7)
8. Synthesis and catalytic applications of amine interacted Cu2(OH)PO4
nanoplates (copper NPs) and tubes (copper NTs), Peta Sreenivasulu,
Nagabhatla Viswanadham, Devaki Nandan, L. N. Sivakumar Konathala and
B. Sreedhar, RSC Advances, 2013, 3, 729. (Impact Factor 3.7)
9. Catalytic performance of nano crystalline H-ZSM-5 in ethanol to gasoline
(ETG) reaction, Nagabhatla Viswanadham, Sandeep K. Saxena, Jitendra
Kumar, Peta Sreenivasulu, Devaki Nandan, Fuel, 2012, 95, 298. (Impact
Factor 3.357)
10. Sulfated Galactans of Champia indica and Champia parvula (Rhodymeniales,
Rhodophyta) of Indian Waters, Sanjay Kumar, Devaki Nandan, Ramavatar
Meena, Kamalesh Prasad and Arup K. Siddhanta, Journal of
Carbohydrate Chemistry, 2011, 30, 47. (Impact Factor 1.18)
Chapter 7. Concluding Remarks and Future Prospects
Ph.D. Thesis of Mr. Devaki Nandan Page 177 CSIR-IIP
7.6 List of Patents Applied/Filled
1. Nagabhatla Viswanadham and Devaki Nandan, Sulfonated carbon silica
composite material and process for the preparation US8722573
2. N Viswanadham, Peta Sreenivasulu, Sandeep K Saxena, Rajiv Panwar,
Devaki Nandan and Jagdish Kumar, A single-step catalytic process for
conversion of naphtha to diesel-range hydrocarbons, WO 2014073006 A4
7.7 Papers presented/accepted in conference, symposium and Seminar
1. Development of functionalized hierarchical carbon-silica composite material
for catalytic applications. Devaki Nandan, Amit Sharma, Sandeep Saran,
Deependra Tripathi and Nagabhatla Viswanadham, "22nd
National
Symposium on Catalysis, CSIR-CSMCRI, Bhavnagar" held on 7-9 January
2015.
2. A novel method for the synthesis of hierarchical ZSM-5 for catalytic
applications. Devaki Nandan, Peta Sreenivasulu, K. L. N. Sivakumar,
Raghuvir Singh and Nagabhatla Viswanadham, Poster presentation in the
"The National Symposia CATALYSIS FOR SUSTAINABLE
DEVELOPMENT CATSYMP-21" held on Feb 11 to Feb 13, 2013 at
CSIR-IICT Hyderabad.
3. Synthesis and catalytic applications of copper hydroxyl phosphate nanoplates
(copper NPs) and tubes (copper NTs). Peta Sreenivasulu, Devaki
Nandan, Sandeep Saran, G M Bahuguna and Nagabhatla Viswanadham,
Poster presentation in the "The National Symposia CATALYSIS FOR
Chapter 7. Concluding Remarks and Future Prospects
Ph.D. Thesis of Mr. Devaki Nandan Page 178 CSIR-IIP
SUSTAINABLE DEVELOPMENT CATSYMP-21" held on Feb 11 to
Feb 13, 2013 at CSIR-IICT Hyderabad.
4. Chemo-selective catalytic conversion of glycerol as a biorenewable source for
oxygenated additive for the diesel fuel, N Viswanadham, Sandeep K Saxena,
Devaki Nandan, P Sreenivasulu, Basant Kumar and M O Garg, International
Mexican Congress on Chemical Reaction Engineering (IMCCRE 2012),
Ixtapa-Zihuatanejo, Guerrero, Mexico, June 10-15, 2012.
5. Catalytic conversion of ethanol to transportation fuel. Sandeep K.
Saxena, Peta Sreenivasulu, Devaki Nandan, Sarabjeet Singh, N.
Viswanadham, Oral presentationin 8th International Symposium on Fuels
& Lubricants (ISFL) 5-7th March 2012, New Delhi.
6. Synthesis of a sulfonated carbon-silica-meso composite and mesoporous
silica. Devaki Nandan, Peta Sreenivasulu, Sandeep K. Saxena, Nagabhatla
Viswanadham, Poster presentation in Emerging Trends in Chemistry and
Biology Interphase 3-4th
November 2011, Kumaun University, Nainital.