(469a) Support Effects in Heterogeneous Catalysis Using Au Nanoparticles on Oxides: A DFT Analysis

Supported Au nanoparticles have been found to be active for numerous heterogeneously catalyzed reactions [1]. In addition, these catalysts have been found to exhibit a bifunctional behavior, where the combined Au/oxide system works in a synergistic manner, giving lower reaction barriers than those of either the Au or the oxide in isolation [2]. The identity of the support plays a key role in determining the activity of Au/oxide systems, with Au nanoparticles showing different turnover rates when supported on different oxides [2,3]. Although support effects have been observed for individual systems, a fundamental understanding, especially in terms of a common unifying descriptor for the activity of these systems, is poorly understood. In this work, we have studied model Au nanowire supported on a range of oxides – MgO, ZnO, Al₂O₃, Fe₂O₃, ZrO₂ and TiO₂ - to understand how the catalytic properties at the interface of these systems are influenced by the choice of the oxide support. The geometric effect of strain in these systems was minimized by orienting the Au nanowire in non-epitaxial registries on the oxide supports. Water Gas Shift (WGS) is known to be promoted at the interfaces of supported Au/oxide systems [2,4] and have, therefore, been used as a probe reaction in this study. Rigorous DFT calculations were performed for reactive intermediates usually associated with WGS, at the interfaces of the various model Au/oxide systems. Our results correlate well with the experimental trend in WGS reactivity on these systems. In particular, we found the WGS rates to correlate well with experimental water orders and calculated adsorption energies of dissociated water at the interface of Au/oxide, suggesting dissociated water to be a common intermediate involved in kinetically significant reaction steps on all these systems. This combined theoretical and experimental analysis hints at the possibility of a common mechanistic basis for trends in support effects.

References

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[3] Shekhar, M., Wang, J., Lee, W.S., Williams, W.D., Kim, S.M., Stach, E.A., Miller, J.T., Delgass, W.N. and Ribeiro, F.H. JACS 2012, 134, 4700

[4] Williams, W.D., Shekhar, M., Lee, W-S., Kispersky, V., Delgass, W.N., Ribeiro, F.H., Kim, S.M., Stach, E.A., Miller, J.T. and Allard, L.F. JACS, 2010, 132, 14018