Heterogeneous Catalysis for

Green Chemistry

Dr. M. Sankar

Cardiff Catalysis Institute

School of Chemistry

Cardiff University

Cardiff, UK.

02/01/2010

Cardiff Catalysis Institute

Overview of this Presentation

Organic Carbonates using CO2

Synthesis of Cyclic Carbonates

Synthesis of Dimethyl Carbonates

Selective oxidation using Gold nanocrystals based Catalysts

Oxidation of Benzyl Alcohol using Au-Pd Supported on TiO2

Oxidation of Glycerol using supported monometallic Catalysts.

Mt. Kilimanjaro (Africa ). Ice cap is shrinking

Columbia glacier AlaskaGlacier National Park 1914-1997

2008

Global Warming – Visible Effects

CO2 Emission & Possible Solution

Sequestration Utilization

M. A. Scibioh, B. Viswanathan Proc.Indn.Natl.Acad.Sci., 70A (3), 2004.

Various Chemical Transformations using CO2

Monomers Aprotic Organic Solvents Fine Chemical Intermediates

Cyclic Carbonate

Methylating Agent

Carbonylating Agent

Oxygenated fuel additive

Substitute for MTBE

Dimethyl Carbonate

Specific Reactions of Interest

O

R

O

R

O

C

O

CO2+

OO

O

MeOH MeO OMe

OOH

HO++

Cyclic Carbonate

Dimethyl Carbonate

Synthesis of Cyclic Carbonates

O

R

O

R

O

C

O

CO2+

+

Catalytic System-ICatalytic System-I

Na12[WZn3(H2O)2(ZnW9O34)2]46H2O(Zn-W-Sandwich Polyoxometalate)

Dimethylaminopyridine

N

N(CH3)2

Experimental conditions: 0.4 MPa CO2, 10 ml CH2Cl2,

0.0026 mmol of Zn-POM, DMAP = 3 mole equivalent Zn POM

Typical Reaction Data

Substrate Product Temp(deg C)

Time (Hrs)

Conv (%)

Selectivity(%)

140 3 98 98

160 9 96 97

160 12 99 97

O O

O

ClCl

O

O

CH3

O O

O

CH3

O

H

O O

O

H

Experimental conditions: 0.4 MPa CO2, 0.0026 mmol of Zn-POM, DMAP = 3

mole equivalent Zn POM

Data Continued…….

Substrate Temp(deg C)

Time (Hrs)

Conv (%)

Selectivity(%)

140 3 98 98

(without solvent)

140 3 99 98

(Recovered POM)

140 3 99 98

Cl

O

Cl

O

Cl

O

Experimental conditions: 0.4 MPa CO2, 10 ml CH2Cl2,

0.0026 mmol of Zn-POM, DMAP = 3 mole equivalent Zn POM

Data Continued…..

Substrate Sub: Cat ratio

Temp(deg C)

Time (Hrs)

Conv (%)

Selectivity(%)

10,000 140 3 97 98

25,000 140 3 98 98

50,000 140 3 84 98

Cl

O

Cl

O

Cl

O

2 0 0 3 0 0 4 0 0 5 0 0

B e f o r e

A f t e r

W a v e l e n g t h , n m

1200 800 400

After

Before

Wavenumber, cm-1

Structural Integrity of Zinc - Polyoxometalate

Proposed mechanism

+

_

O

ZnO CO2

, O

R

N

N(CH3)2

OZn

O

CO O O

RN

N(CH3)2

OZn

O

CO O

O

R

OZn

O

OC

O

O

R

N

N(CH3)2

-

Very high Substrate Vs Catalyst Ratio

Reaction without organic solvent – atom economy

Applicable to a range of epoxides

Polyoxometalate part is Recoverable and reusable

First ever Polyoxometalate based catalyst system

for this particular reaction

Highlights

M. Sankar, N. Tarte, P. Manikandan, Appl. Catal. A. 276 (2004) p.217. US Patent - 6,924,379 Indian Patent - Granted

Catalytic System-IICatalytic System-II

Si

Si-O

Si-O

Si-O

NN

Si

Si-OH

Si-O

Si-O

NN

OH

I II

and/or

Si

EtO

EtO

EtO

NHN

Si-OH

Si-OH

Si-OH

+

Silica

Cl +

Chloropropyl triethoxy silane Imidazole

L. T. Aany Sofia, Asha Krishnan, M. Sankar, N. K. Kala Raj, P. Manikandan, P. R. Rajamohanan, and T. G. Ajithkumar* J. Phys. Chem. C 113 (2009), 21114.

Si

Si-O

Si-O

Si-O

NN Si

Si-OH

Si-O

Si-O

NN

OH

Si-NMR of Fumed Silica Si-NMR of Functionalised Silica

Solid State NMR Characterization

Si

Si-O

Si-O

Si-O

NN

13C NMR of Functionalised Silica

0 5 10 15 200

20

40

60

80

100

p(CO2): 10 bar

120oC

70oC

90oC

Ep

oxid

e C

on

vers

ion

, (%

)

Time (h)

Cl CO2

O+

OO

O

Cl

1 2 3 40

20

40

60

80

100

: Epoxide Conv, : Cyclic Carbonate, : Others

Con

vers

ion

/ Sel

ectiv

ity,

%

Number of Catalytic Cycles

Reaction Data

Temperature Effect Recycle Studies

Catalyst Epoxide Temp/Time Epox Conv CC Selec

Si-Imid ECH 120 °C/4 h 98 98

No Catalyst ECH 120 °C/4 h <5 0

Si-Imid PO 130 °C/10 h 99 99

Si-Imid BO 130 °C/10 h 99 94

Si-Imid SO 130 °C/10 h 79 97

O

Cl

OO O

ECH PO BO SO

Catalyst Activity

150 120 90 60 30 0

*: CC**

*

ppm

Structural Stability – MAS-NMR

-180 -150 -120 -90 -60 -30 0

13C

29Si

Fresh

Recovered

Fresh

Recovered

Proposed - Mechanism

N

N

CO O

O

R

O

CO

O

R

O

R

Si

Si-O

Si-O

Si-O

NN

_

+

M.Sankar et.al., (Manuscript under preparation)

Highlights

Single Site – Heterogeneous Catalyst

Recoverable and Reusable

Easy to synthesize

Relatively mild reaction condition

CO2 : 6-10 bar, Temp: 90-130 ºC, Time: 4-10 h

Yield : > 96 %, Solvent: No Recoverable & Reusable: Yes

R = H, Cl, CH3

Cyclic Carbonate

R CO2

O+

OO

O

R

Zn-POM/DMAP

(or) Si-Imid

Summary

OO

O

MeOH MeO OMe

OOH

HO++

Synthesis of Dimethyl carbonate

 

Exp. Cond. EC/PC : 50mmol, Methanol : 500mmol

Catalyst: 1gm p-Xylene : 1gm Time: 5hrs

Sl.No.

Subs Catalyst TempoC

DMC Yield(%)

1 EC Na2WO4.2H2O 25 79

2 EC Na2WO4.2H2O

(I-Recov)

25 78

3 PC Na2WO4.2H2O 25 23

4 EC CaWO4 25 79

5 EC Li2WO4 25 66

6 EC K2WO4 25 71

7 EC Na2VO3 25 79

Catalytic System-I

Catalysis Data

0 1 2 3 4 50

20

40

60

80

10 °C 25 °C 50 °C 100 °C

DMC

Yield

(%)

Time (h)

Effect of Temperature

0 2 40

20

40

60

80

With MgO

After catalyst filteration at 1 h

With Catalyst

DM

C Y

ield

(%)

Time (h)

Heterogeneous Catalyst

20 40 60 80

4000 3500 3000 2500 2000 1500 1000

(b)

(a)

Fresh

Recovered

Wavenumber (cm-1)

Powder XRD

IR

Structural Integrity of Sodium Tungstate

1200 1000 800

Wavenumber (cm-1)

4000 3500 3000

(b)

(a)

1100 1000 900

FT-IR

Raman

1062

1030

8 min

6 min

4 min

2 min

0 min

Adsorbed CH3O-

CH3OH

Adsorbed CH3O -

Active Intermediate: IR and Raman Studies

O

O

O

MeO-

MeO-

OH

OH

O

O

O-

OMe

MeOH

O-

OH

O

O-

O

OMe

MeO

MeO

O

MeOH

O

OH

OMe

OMe

-O

O

OH

O

OMe MeO-+

++

Proposed Mechanism DMC formation

M. Sankar, N. Madhavan Nair, K.V.G.K. Murty, P. Manikandan, Appl. Catal. A. 312 (2006) p.108.

US Patent – Applied Indian Patent - Applied

Highlights

Active at room temperature

No CO2 pressure – pot reaction

Recoverable & Reusable

No complicated synthesis

Selective Oxidation using “Green” Oxidants

Introduction: Au and Au-Pd nanoparticles based catalysts have been reported to be very effective for :

Epoxidation of Alkenes: Hutchings et.al., Nature (2005).

Direct synthesis of Hydrogen Peroxide: Hutchings et.al., Science (2009).

Oxidation of Primary Alcohols: Hutchings et.al., Science (2006),

In this Presentation:

Oxidation of Benzyl Alcohol : Mechanistic Investigation

Oxidation of Bio-renewable Feedstocks : Glycerol Oxidation

0 2 4 6 8 10 12 14 16 18 20 22 240

10

20

30

40

50

60

70

80

90

100

Time/h

Be

nzy

alc

oh

ol c

on

vers

ion

/%

0

10

20

30

40

50

60

70

80

90

100

Be

nza

lde

hyd

e se

lectivity/%

Benzyl alcohol conversion and selectivity in benzaldehyde with the reaction time at 100 oC, 0.2 MPa O2 pressure: () Au/TiO2, ()Pd/TiO2, () Au-Pd/TiO2; solid symbols – conversion, open symbols – selectivity Science 2006AuPd nanoparticles prepared by impregnation1-50 nm Au-rich core, Pd-rich surface

Oxidation of Benzyl Alcohol using Au-Pd supported on TiO2

Aim is to understand the origin of Toluene in the “Solventless” oxidation of Benzyl alcohol and thereby “switching off” the toluene production

Experimental

50 ml Glass Reactor

Stirred at 1000 rpm – No mass transport limitations

Analysed by GC using mesitylene as external standard

Rates of the reaction were calculated for the first 10% conversion level

Catalyst Synthesis:

(Au-Pd)/TiO2, Au/TiO2, Pd/TiO2 by Sol-immobilization technique1

Catalytic Reaction (3 phase system: solid/liquid/gas)

1 J.A. Lopez-Sanchez, N. Dimitratos, P. Miedziak, E. Ntainjua, J.K. Edwards, D. Morgan, A.F. Carley, R. Tiruvalam, C.J. Kiely and G.J. Hutchings, Phys.Chem. Chem. Phys, 2008, 10, 1921.

Initial rates of reaction under oxygen at 80oC

Catalyst Benzyl Alcohol Benzaldehyde Toluene

d[BzOH]/dt( 10-7 mol s-1)

R2 d[Ald]/dt( 10-7 mol s-1)

R2 d[Tol]/dt( 10-7 mol s-1)

R2

1%(Au-Pd)/TiO2 -5.420 ± 0.46 0.986 4.810 ± 0.46 0.982 0.755 ± 0.151 0.950

0.5%Au/TiO2 -0.032 ± 0.0047 0.989 0.0316 ± 0.0044 0.990 0.000237 ± 0.0001 0.921

0.5%Pd/TiO2 -0.376 ± 0.09 0.947 0.359 ± 0.0857 0.948 0.00158 ± 0.0064 0.869

Catalyst: 0.02g Benzyl Alcohol: 1g O2: 1 bar Stirring: 1000rpm

Initial rates of reaction under He at 80oC

Catalyst Benzyl Alcohol Benzaldehyde Toluene

d[BzOH]/dt( 10-7 mol s-1)

R2 d[Ald]/dt( 10-7 mol s-1)

R2 d[Tol]/dt( 10-7 mol s-1)

R2

1%(Au-Pd)/TiO2 - 0.795 ± 0.043 0.959 0.422 ± 0.024 0.966 0.373 ± 0.027 0.941

0.5%Au/TiO2 -0.0367 ± 0.0032 0.992 0.0373 ± 0.002 0.997 0.000494 ± 0.000114 0.951

0.5%Pd/TiO2 - 0.404 ± 0.130 0.910 0.260 ± 0.078 0.921 0.144 ± 0.056 0.877

Catalyst: 0.02g Benzyl Alcohol: 1g He: 1 bar Stirring: 1000rpm

Monometallic versus Bimetallic Catalysts

No reaction in the absence of catalyst

Reaction of PhCH2OH versus PhCD2OH

0 1 2 3 4 5 6 7 8 9 108.4

8.5

8.6

8.7

8.8

8.9

9.0

Time/ 103s

BzO

H /

10

-3 m

ole

s

H BzOH

D BzOH

Rate of disappearance of benzyl alcohol ▲(Proton) ● (Deuterated) under 1 bar He

Under Oxygen (1 bar)

Substrate Benzyl Alcohol Benzaldehyde Toluene

d[BzOH]/dt( 10-7 mol s-1)

R2 d[Ald]/dt( 10-7 mol s-1)

R2 d[Tol]/dt( 10-7 mol s-1)

R2

PhCH2OH -5.42 ± 0.46 0.986 4.808 ± 0.46 0.982 0.755 ± 0.15 0.950

PhCD2OH -2.05 ± 0.14 0.993 1.867 ± 0.13 0.993 0.222 ± 0.03 0.974

KIE 2.65 2.58 3.41

Substrate: 1g Catalyst: 0.02g O2: 1bar Stirring: 1000 rpm Temp: 80oC

Deuterium NMR (coupled) of the reaction mixture (inset toluene peak magnified)

10 8 6 4 2 0

1.2 0.9 0.6

-CDO(Singlet)

CDCl3

BzOH

-CD3/CD

2H (Doublet)

-CD3/CD

2H Peak

Chemical Shift (ppm)

GC- Mass analysis of the reaction mixture – Comparison of protonated toluene and deuterated toluene part alone shown for clarity.

Effect of atmosphere on the initial rate of reaction

Gas/Press Benzyl Alcohol Benzaldehyde Toluene

d[BzOH]/dt( 10-7 mol s-1)

R2 d[Ald]/dt( 10-7 mol s-1)

R2 d[Tol]/dt( 10-7 mol s-1)

R2

He -0.795 ± 0.04 0.959 0.422 ± 0.02 0.966 0.373 ± 0.03 0.941

Air -2.288 ± 0.17 0.989 1.454 ± 0.09 0.992 0.832 ± 0.09 0.976

O2 / 1 bar -5.420 ± 0.46 0.986 4.808 ± 0.46 0.982 0.755 ± 0.15 0.950

O2 / 2 bar -6.440 ± 0.29 0.996 5.803 ± 0.29 0.996 0.595 ± 0.05 0.987

O2 / 3 bar -6.313 ± 0.38 0.995 5.862 ± 0.35 0.995 0.464 ± 0.06 0.980

Benzyl Alcohol : 1g Catalyst: 0.02g Temp: 80oC Stirring: 1000 rpm Pressure: 1bar

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.80

1

2

3

4

5

6

7

8

1 / VOH

1 / VAld

1 / VTol

1/[BzOH] mol / Kg

1/ V

To

l/ 10

7 m

ol /

Kg

s-1

Effect of dilution with o-xyleneLineweaver-Burk plot of initial rates versus formal concentration of benzyl alcohol

Derive vmax & Kd

Kd ald << Kd tolActive site for the two products

Appears to be different

PhCH2HC

HO Ph HC

PhHOO

O.H

COO. Ph H

H

HO H

H

PHe PO1

PO2

Speculation on mechanism & structure of precursor states

PhCH2OHPhCH2OH

CATPHe

PhCHO

PhCH3

PhCH2OH/O2

CAT

PO1

PO2

PhCHO

PhCH3

O2

He

M. Sankar et.al., Faraday Discussions, 2009 (In Press)

Glycerol Oxidation – Possible Products

Oxidation of Glycerol in an autoclave reactor using O2 or aq. H2O2

M.Sankar, N. Dimitratos,D. W. Knight, A. F. Carley,R. Tiruvalam,C. J. Kiely, D.Thomas,and G. J. Hutchings*, ChemSusChem, 2010 (In press)

Acknowledgements

Dr. P. Manikandan, NCL Pune

Prof. Graham J Hutchings, Cardiff University

Prof. David W Knight, Cardiff University

Prof. Donald Bethell, Liverpool University

Dr. S. Sivasanker, NCCR, Chennai

Prof. B. Viswanathan, NCCR, Chennai

EPSRC & CSIR