Hydrogen peroxide formation on AuPd nanoparticles Rasmus Svensson and Henrik Grönbeck Department of Physics and Competence Centre for Catalysis, Chalmers University of Technology, Sweden Hydrogen peroxide, H 2 O 2 , is an important industrial chemical, thanks to its mild oxidizing character and small environmental impact [1]. The desire for green, energy-efficient, small-scale synthesis of H 2 O 2 has sparked theneed for efficient catalysts for the direct formation of H 2 O 2 from O 2 and H 2 . In this work we have explored,and kinetically analyzed, critical steps for the heterogeneous catalytic formation of H 2 O 2 over single atomalloy palladium doped gold nanoparticles. In particular, density functional theory (DFT) calculations havebeen performed to establish the potential energy landscape and kinetic Monte Carlo simulations using scalingrelations have been applied to determine the reaction kinetics. The reaction is investigated with respect toparticle shape, size and degree of alloying. Gold alloys exothermically with palladium for all Au:Pd-ratios [2], entailing the possibility of high ratios of palladium monomers in dilute palladium gold nanoparticles. However, due to the low surface energy of gold, the probability of finding palladium at the surface of the particle is reduced under vacuum conditions. The situation is different under high oxygen and hydrogen pressures, where the presence of adsorbates stabilize palladium at the surface. In the catalytic formation of H 2 O 2 , several critical steps have been identified, of which, both palladium and gold play crucial parts. Firstly, oxygen should adsorb, but not dissociate, on the surface. This can be done on the palladium monomers, whereas larger patches of palladium results in scission of the O-O bond. Secondly, hydrogen should adsorb and dissociate over palladium atoms. This is an important role of the palladium atoms on the surface, as hydrogen does not dissociate on pure gold surfaces. Moreover, atomic hydrogen may diffuseover gold surfaces without being desorbed, owing to a large desorption barrier. The fact that hydrogen maydiffuse over the gold surface enables the possibility for reaction paths where multiple palladium monomersare involved during the formation of H 2 O 2 . The cleavage of the O–O, O–OH and HO–OH bonds must beprevented along the reaction path, as it leads to irreversible formation of water. The inert properties of gold playsin this respect an important role as, for example, desorption of H 2 O 2 is preferred with respect to dissociationinto 2OH. We found that the desorption energy of H 2 O 2 from the gold surfaces are clearly lower than thecorresponding palladium rich surfaces [3]. This work highlights the different roles of different sites in a catalytic reaction. The work stresses that it is the ensemble of sites rather than one active site that determines the activity of alloy nanoparticles. References 1. J. M. Campos-Martin, G. Blanco-Brieva, and J. L. Fierro, Angewandte Chemie International Edition, vol. 45, no. 42, pp. 6962–6984, 2006.
2. H. Okamoto and T. Massalski, Bulletin of Alloy Phase Diagrams, vol. 6, no. 3, pp. 229–235, 1985. 3. L. Chen, J. W. Medlin, and H. Grönbeck, ACS Catalysis, vol. 11, no. 5, pp. 2735–2745, 2021.
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