Au–Pd separation enhances bimetallic catalysis of alcohol oxidation Xiaoyang Huang 1,7 , Ouardia Akdim 1,7 , Mark Douthwaite 1 , Kai Wang 1 , Liang Zhao 1 , Richard J. Lewis 1 , Samuel Pattisson 1 , Isaac T. Daniel 1 , Peter J. Miedziak 1,2 , Greg Shaw 1 , David J. Morgan 1 , Sultan M. Althahban 3,4 , Thomas E. Davies 1 , Qian He 1,5 , Fei Wang 1 , Jile Fu 1 , Donald Bethell 1 , Steven McIntosh 6 , Christopher J. Kiely 3,6 and Graham J. Hutchings 1 1 Max Planck-Cardiff Centre on the Fundamentals of Heterogeneous Catalysis FUNCAT, Cardiff Catalysis Institute, School of Chemistry, Cardiff University, UK. 2 School of Applied Sciences, University of South Wales, UK. 3 Department of Materials Science and Engineering, Lehigh University, USA. 4 Department of Mechanical Engineering, Jazan University, Saudi Arabia. 5 Department of Materials Science and Engineering, Faculty of Engineering, National University of Singapore, Singapore. 6 Department of Chemical and Biomolecular Engineering, Lehigh University, USA. 7 These authors contributed equally. Bimetallic Au-Pd catalysts are well known to give significant rate enhancements over their monometallic analogues. This has been demonstrated for a range of reactions including the oxidative dehydrogenation (ODH) of alcohols. 1 The rate of oxygen reduction (ORR) occurring within these systems is crucial, 2 and the opposing activity of supported Au and Pd nanoparticles for ORR is well documented, with Pd known to be very effective. 3 Here, we show that by separating the Au and Pd catalytic sites during the ODH of 5-hydroxymethylfurfural (amongst other alcohols), the activity is almost doubled compared to that of a typical alloy. It is proposed that the bimetallic rate enhancement is due to the coupling of two redox processes occurring over isolated Au and Pd sites. The heightened enhancement when using a physical mixture of monometallic catalysts over that of an alloy is attributed to the ability of the individual metal sites to maintain their full redox capabilities. Using both thermo- and electrocatalytic analysis, ODH is demonstrated to occur over Au sites with ORR catalysed by Pd sites. The conductivity of the support used is proven to be vital, indicating the importance of electron transfer between the two metals. The coupling is further demonstrated by the fact that when the mass of Pd catalyst is increased in a physical mixture system containing a constant amount of Au, the rate of ODH is indirectly increased through an increase in the rate of ORR. This cooperative redox enhancement (CORE) is a novel observation that offers new avenues when considering the design of bimetallic catalytic systems. References 1. Wang, D., Villa, A., Porta, F., Prati, L. & Su, D. Bimetallic gold/palladium catalysts: Correlation between nanostructure and synergistic effects. J. Phys. Chem. C 112 , 8617–8622 (2008). 2. B. N. Zope, D. D. Hibbitts, M. Neurock and R. J. Davis, Science , 2010, 330 , 74–78. 3. A. Kulkarni, S. Siahrostami, A. Patel and J. K. Nørskov, Chemical Reviews , 2018, 118 , 2302–2312.
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