Strategies to Synthesize Supported Bimetallic Catalysts

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2 Strategies to Synthesize Supported Bimetallic Catalysts M. Sankar Cardiff Catalysis Institute School of Chemistry Cardiff University, Cardiff United Kingdom

3 Outline Ø Supported Bimetallic Catalysts Ø Controlling Size, Composition & Nanostructure Supported AuPd Catalysts Ø Tuning Selectivity Supported AuPd Catalysts

4 Why bimetallic catalysts? Selective Aerobic Oxidation of Alcohols OH O O 2 - H 2 O Catalytic Activity (TON x 10 5 ) Is this synergistic-effect an odd example? Au Pd AuPd Supported Metal Catalysts Enache et al. Science, 2006, 311, 362

5 Why bimetallic catalysts? Hydrogenation of Levulinic Acid to γ-valerolactone Catalytic Activity (Conv (%)) %AuPd/TiO 2 1%Au/TiO %Pd/TiO Time / min Luo, Sankar et al. Nature Communications, (2015 ) 6, 6540

6 Bimetallic catalysts Industrial relevance Research on bimetallic catalysts has had major impact in the reforming of petroleum naphtha fractions to produce high octane number components for gasolines. During the 1970s, bimetallic catalysts largely replaced traditional Pt catalysts in reforming. This development has been an important factor in the emergence of low-lead and lead-free gasolines. - John H Sinfelt, Exxon Monograph on Bimetallic catalysts

7 The art of synthesizing catalyst Direct Synthesis of Hydrogen Peroxide Catalytic Activity (H 2 O 2 Productivity) Fresh 1 st Reuse 2 nd Reuse S1 S2 S3 S4 S5 S6 S7 S8 0.5 % Au - 0.5% Pd / TiO 2 Sankar et al. ACS Nano 2012, 6, 6600

8 Synthesis strategy-1: Conventional wetimpregnation (CIm) Edwards et al. Faraday Discuss., 2008, 138, 225 Support HAuCl 4 PdCl 2 High Temperature Calcination Water Dried at 90 o C Dried Catalyst 450 o C / 4h Supported AuPd Catalysts

9 Particle size distribution for CIm catalyst Edwards et al. Faraday Discuss., 2008, 138, 225 Ac#ve Inac#ve

10 Composition analysis using SEM XEDS

11 Size dependent compositional variation Edwards et al. Faraday Discuss., 2008, 138, 225 Small Particle (Palladium Rich) Intermediate Particle (Mixture) Large Particle (Gold Rich)

12 Nanostructure of the AuPd catalyst (CIm) Au (core) Pd (shell) TiO 2 Enache et al. Science, 2006, 311, 362

13 Structural issues for bimetallic catalysts Sankar et al. Chem. Soc. Rev. 2012, 41, 8099 Particle Size Mixing Pattern (Nanostructure) Composition Variation

14 Synthesis strategy 2: Sol immobilization method (SIm) for controlling size Dimitratos et al. Phys. Chem. Chem. Phys., 2009, 11,

15 Size dependent compositional variation (SIm) Small Particle (Gold Rich) Intermediate Particle (Mixture) Large Particle (Palladium Rich)

16 Synthesis strategy 3 : Modified Wet-Impregnation (MIm) Support (P25-TiO 2 ) HAuCl 4 PdCl 2 Gas Phase Reduction dil. HCl Dried at 90 o C Excess of anion (Cl - ) 5%H 2 / He Dried Catalyst 400 o C / 4h AuPd/TiO 2 Catalyst Sankar et al ACS Nano 2012, 6, 6600

17 Effect of [Cl - ] on particle size 0 M HCl (CIm) 0.58 M HCl (MIm) 2 M HCl (MIm) 0 M HCl (CIm) 0.58 M HCl (MIm) 2 M HCl (MIm)

18 [Cl - ] vs Composition : 0.5%Au-0.5%Pd/TiO 2 0 M HCl (CIm) 0.58 M HCl (MIm) 2 M HCl (MIm)

19 Controlling the size & composition of AuPd Nanoalloys 0 M HCl (CIm) Increase in [Cl - ] Size decreases 0.58 M HCl (MIm ) 2 M HCl (MIm) & Au content increases

20 Nanostructure Control (Random Alloy Vs Core-Shell) CIm - Calcined MIm - Reduced MIm - Calcined Core-Shell Random Alloy Core-Shell Sankar et al ACS Nano 2012, 6, 6600

21 Catalytic results : structure activity correlation Productivity (mol H2O2 kg cat -1 h -1 ) Random Alloy SDCV Core-Shell SDCV Fresh Reuse-1 Reuse-2 NO SDCV Random Alloy NO SDCV Core-Shell NO SDCV "Gold Rich" "Gold Rich" Big Particles 0 CIm SIm MIm MIm MIm MIm MIm MIm Calc Dried Dried Red Calc Red Red Red 0.5%Au 0.5%Pd / TiO 2 Sankar et al ACS Nano 2012, 6, 6600

22 SIm vs MIm for benzyl alcohol oxidation : [Micro packed bed reactor (MPBR)] Morad et al. Catal. Sci.Technol. 2014, 4, 3120

23 Catalytic Activity (Conv (%)) Supported AuPd Catalyst for Biomass Valorisation Reaction Hydrogenation of Levulinic Acid to γ-valerolactone 1%AuPd/TiO 2 1%Au/TiO %Pd/TiO Time / min Alloying two relatively inactive metals increases the activity Luo, Sankar et al. Nature Communications, (2015 ) 6, 6540

24 Replacing Au with Ru RuPd Catalyst for Biomass Conversion Hydrogenation of Levulinic Acid to γ-valerolactone Bimetallic RuPd system Activity of this catalyst gives >99% selectivity to depends on the synthesis GVL even after 3h strategy Sankar et al. European patent application filed (2014)

25 Reusability of the bimetallic catalysts 1%RuPd/TiO2 1%AuPd/TiO % % GVL yield at 20 min GVL yield at 30 min selectivity of GVL at 120 min 0 GVL yield at 3 h GVL yield at 4 h selectivity of GVL at 4 h Bimetallic catalysts are reusable without any lose of activity

26 Stability of the metal particles (Monometallic vs Bimetallic) Bimetallic catalysts do not sinter

27 Mapping of homogeneous random alloy (1%RuPd/TiO 2 ) HAADF RG overlay Ru map ( kev) Pd map ( kev)

28 Summary v Chloride ions (NOT always BAD!!!) (Composition & Size Control) v Too much gold Not stable v Replace Au with Ru Stable v Calcination Gold Core Palladium Shell - Less Active v Reduction Homogeneous Random Alloy - Active

29 Selectivity Tuning During Aerobic Oxidation Sankar et al. Faraday Discussions 2010, 145, 341. Disproportionation reaction origin of toluene OH O 2 + +H 2 O benzyl alcohol toluene benzaldehyde Oxidation reaction origin of aldehyde and acid OH O O O 2 -H 2 O O 2 OH benzyl alcohol benzaldehyde benzoic acid

30 Catalyst Designing to switch-off Toluene Catalyst Conversion (%) Benzaldehyde Selectivity (%) Toluene 1%AuPd/TiO %AuPd/Nb 2 O %AuPd/C %AuPd/MgO %AuPd/ZnO Sankar et al. Chem. Eur. J. 2011, 17, 6524

31 Separation & quantification of the two reactions PhCH 2 OH PhCH 3 + PhCHO + H 2 O Disproportionation Oxidation 2PhCH 2 OH PhCH 3 + PhCHO + H 2 O PhCH 2 OH PhCHO + H 2 O (TON D )=2 * mol tol /mol metal (TON O ) = (mol PhCHO mol tol )/mol metal DISPROPORTIONATION REACTION OXIDATION REACTION Active site : metal-support interface Active site : metal nanoparticles Sankar et al. Chem. Eur. J. 2011, 17, 6524

32 Proposed mechanism - disproportionation Nowicka et al. Phys. Chem. Chem. Phys. 2013, 15, 12147

33 Overall Summary Catalyst synthesis strategy Structure - Activity - Catalyst synthesis Valorisation reactions Bimetallic catalysts for Biomass valorisation reaction Selectivity tuning Reaction identification-reaction mechanism-catalyst design

34 Acknowledgement Prof. G. J. Hutchings Cardiff University Prof. C. J. Kiely Leheigh Univesity Dr. Q. He Leheigh University Prof. D. Bethell, Liverpool University Collaborators Prof. D.W. Knight Cardiff University Dr. E. Nowicka Cardiff University Dr. N. Dimitratos Cardiff University Dr. J. Pritchard Cardiff University Prof. B. M. Weckhuysen Utrecht University Funding Prof. A. Gavriilidis University College London Dr. M. Morad Cardiff University Dr. A. Carley Cardiff University Dr. P. C. A. Bruijnincx Utrecht University

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