The unique catalytic activity of supported nanoparticles versus their bulk counterparts is often attributed to electronic interactions with the support that result in charge transfer, structural changes or creation of new active sites at the particle-support interface. For oxide supported Cu catalysts, which are of interest for promoting the water-gas-shift (WGS) reaction and methanol synthesis, the metal oxide-Cu electronic interactions are known to strongly influence activity. In this work, we are using size-selected deposition to explore the interfacial electronic structure of a number of small metal oxide clusters (Mo, W, Ti, Nb) on Cu(111) and Cu2O/Cu(111) surfaces as model �inverse� catalysts. Such inverse systems are useful for investigating the chemical role of the oxide, and in some cases, can be even more active than the conventional catalysts as a result of electronic modifications induced by the metal substrate, e.g., higher state of reduction. The extent and direction of charge transfer at the interface are extracted from coverage dependent work function measurements using two-photon photoemission (2PPE) and theoretical DFT calculations. The trends observed for charge transfer are correlated with their ability to dissociate adsorbed water molecules, which is an important step in the WGS reaction. As O-vacancies can play an important role for adsorbate binding and water dissociation on oxide surfaces, both stoichiometric and sub-stoichoimetric oxide clusters, e.g., Nb4O10 and Nb4O7 clusters, are being studied. These studies highlight the unique ability of cluster deposition to prepare well-defined �reduced� surface oxides by controlling the stoichiometry of the clusters rather than by post-deposition heating or chemical treatments.

Interfacial charge transfer and reactivity of supported metal oxide nanoclusters

248th National Meeting (2014)

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