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 CO 2  Synthesis of Cyclic Carbonates  Synthesis of Dimethyl Carbonates  Selective oxidation using Gold nanocrystals based Catalysts  Oxidation of Benzyl Alcohol using Au-Pd Supported on TiO 2  Oxidation of Glycerol using supported monometallic Catalysts.

Mt. Kilimanjaro (Africa ). Ice cap is shrinking Columbia glacier Alaska Glacier National Park Global Warming – Visible Effects

CO 2 Emission & Possible Solution Sequestration Utilization M. A. Scibioh, B. Viswanathan Proc.Indn.Natl.Acad.Sci., 70A (3), 2004.

Various Chemical Transformations using CO 2  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 Cyclic Carbonate Dimethyl Carbonate

Synthesis of Cyclic Carbonates

+ Catalytic System-I Na 12 [WZn 3 (H 2 O) 2 (ZnW 9 O 34 ) 2 ]46H 2 O (Zn-W-Sandwich Polyoxometalate) Dimethylaminopyridine

Experimental conditions: 0.4 MPa CO 2, 10 ml CH 2 Cl 2, mmol of Zn-POM, DMAP = 3 mole equivalent Zn POM Typical Reaction Data Substrate Product Temp (deg C) Time (Hrs) Conv (%) Selectivity (%)

Experimental conditions: 0.4 MPa CO 2, mmol of Zn-POM, DMAP = 3 mole equivalent Zn POM Data Continued……. SubstrateTemp (deg C) Time (Hrs) Conv (%) Selectivity(%) (without solvent) (Recovered POM)

Experimental conditions: 0.4 MPa CO 2, 10 ml CH 2 Cl 2, mmol of Zn-POM, DMAP = 3 mole equivalent Zn POM Data Continued….. SubstrateSub: Cat ratio Temp (deg C) Time (Hrs) Conv (%) Selectivity (%) 10, , ,

Structural Integrity of Zinc - Polyoxometalate

Proposed mechanism

 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-II Si Si-O Si-O Si-O N N Si Si-OH Si-O Si-O N N OH I II and/or Si EtO EtO EtO NH N 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),

Si-NMR of Fumed SilicaSi-NMR of Functionalised Silica Solid State NMR Characterization

13 C NMR of Functionalised Silica

Reaction Data Temperature EffectRecycle Studies

Catalyst Epoxide Temp/TimeEpox ConvCC Selec Si-ImidECH120 °C/4 h98 No CatalystECH120 °C/4 h<50 Si-ImidPO130 °C/10 h99 Si-ImidBO130 °C/10 h9994 Si-ImidSO130 °C/10 h7997 ECHPO BO SO Catalyst Activity

Structural Stability – MAS-NMR 13 C 29 Si Fresh Recovered Fresh Recovered

Proposed - Mechanism M.Sankar et.al., (Manuscript under preparation)

Highlights  Single Site – Heterogeneous Catalyst  Recoverable and Reusable  Easy to synthesize  Relatively mild reaction condition

 CO 2 : 6-10 bar, Temp: ºC, Time: 4-10 h  Yield : > 96 %, Solvent:No Recoverable & Reusable: Yes R = H, Cl, CH 3 Cyclic Carbonate Summary

Synthesis of Dimethyl carbonate

Exp. Cond. EC/PC : 50mmol, Methanol : 500mmol Catalyst: 1gm p-Xylene : 1gm Time: 5hrs Sl. No. Subs Catalyst Temp o C DMC Yield(%) 1ECNa 2 WO 4.2H 2 O2579 2ECNa 2 WO 4.2H 2 O (I-Recov) PCNa 2 WO 4.2H 2 O2523 4ECCaWO ECLi 2 WO ECK 2 WO ECNa 2 VO Catalytic System-I

Catalysis Data Effect of TemperatureHeterogeneous Catalyst

Powder XRD IR Structural Integrity of Sodium Tungstate

Adsorbed CH 3 O - CH 3 OH Adsorbed CH 3 O - Active Intermediate: IR and Raman Studies

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 CO 2 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

Benzyl alcohol conversion and selectivity in benzaldehyde with the reaction time at 100 o C, 0.2 MPa O 2 pressure: () Au/TiO 2, (  )Pd/TiO 2, (  ) Au-Pd/TiO 2 ; solid symbols – conversion, open symbols – selectivity Science 2006 AuPd nanoparticles prepared by impregnation 1-50 nm Au-rich core, Pd-rich surface Oxidation of Benzyl Alcohol using Au-Pd supported on TiO 2 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)/TiO 2, Au/TiO 2, Pd/TiO 2 by Sol-immobilization technique 1 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 80 o C CatalystBenzyl AlcoholBenzaldehydeToluene d[BzOH]/dt ( mol s -1 ) R2R2 d[Ald]/dt ( mol s -1 ) R2R2 d[Tol]/dt ( mol s -1 ) R2R2 1%(Au-Pd)/TiO ± ± ± %Au/TiO ± ± ± %Pd/TiO ± ± ± Catalyst: 0.02g Benzyl Alcohol: 1g O 2 : 1 bar Stirring: 1000rpm Initial rates of reaction under He at 80 o C CatalystBenzyl AlcoholBenzaldehydeToluene d[BzOH]/dt ( mol s -1 ) R2R2 d[Ald]/dt ( mol s -1 ) R2R2 d[Tol]/dt ( mol s -1 ) R2R2 1%(Au-Pd)/TiO ± ± ± %Au/TiO ± ± ± %Pd/TiO ± ± ± Catalyst: 0.02g Benzyl Alcohol: 1g He: 1 bar Stirring: 1000rpm Monometallic versus Bimetallic Catalysts No reaction in the absence of catalyst

Reaction of PhCH 2 OH versus PhCD 2 OH Rate of disappearance of benzyl alcohol ▲(Proton) ● (Deuterated) under 1 bar He Under Oxygen (1 bar) SubstrateBenzyl AlcoholBenzaldehydeToluene d[BzOH]/dt ( mol s -1 ) R2R2 d[Ald]/dt ( mol s -1 ) R2R2 d[Tol]/dt ( mol s -1 ) R2R2 PhCH 2 OH-5.42 ± ± ± PhCD 2 OH-2.05 ± ± ± KIE Substrate: 1g Catalyst: 0.02g O 2 : 1bar Stirring: 1000 rpm Temp: 80 o C

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

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/PressBenzyl AlcoholBenzaldehydeToluene d[BzOH]/dt ( mol s -1 ) R2R2 d[Ald]/dt ( mol s -1 ) R2R2 d[Tol]/dt ( mol s -1 ) R2R2 He ± ± ± Air ± ± ± O 2 / 1 bar ± ± ± O 2 / 2 bar ± ± ± O 2 / 3 bar ± ± ± Benzyl Alcohol : 1g Catalyst: 0.02g Temp: 80 o C Stirring: 1000 rpm Pressure: 1bar

Effect of dilution with o-xylene Lineweaver-Burk plot of initial rates versus formal concentration of benzyl alcohol Derive v max & K d K d ald << K d tol Active site for the two products Appears to be different

PhCH 2 H C HOPh H C PhHO O O. H CO O. PhH H HO H H PHePO1 PO2 Speculation on mechanism & structure of precursor states PhCH 2 OH PhCH 2 OH CAT PHe PhCHO PhCH 3 PhCH 2 OH/O 2 CAT PO1 PO2 PhCHO PhCH 3 O 2 He M. Sankar et.al., Faraday Discussions, 2009 (In Press)

Glycerol Oxidation – Possible Products

Oxidation of Glycerol in an autoclave reactor using O 2 or aq. H 2 O 2 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