Effect of reducible oxide–metal cluster charge transfer on the structure and reactivity of adsorbed Au and Pt atoms and clusters on anatase TiO2

Abstract

We carried out density functional theory calculations to study the influence of oxide–metal charge transfers on the structure, energetics, and reactivity of Au and Pt atoms, dimers, and trimers adsorbed on the (101) surface of reduced anatase TiO2. Pt clusters interact much more strongly with the TiO2 support than Au clusters, and, with the exception of single Pt adatoms, generally behave as electron acceptors on reduced TiO2, whereas Au clusters can both accept and donate charge on the reduced surface. The reactivity of the supported clusters was probed by considering their interaction with CO and co-adsorbed O2. The effect of surface reduction on the interaction with CO is particularly significant when the CO adsorption site is an interfacial metal atom directly in contact with the TiO2 surface and/or in the presence of co-adsorbed O2. Pt clusters interact strongly with co-adsorbed O2 and form Pt–O2 complexes that can easily accept electrons from reduced surfaces. In contrast, Au clusters donate charge to co-adsorbed O2 even in the presence of excess electrons from a reduced support. The computed differences in the properties of the supported Pt and Au clusters are consistent with several experimental observations and highlight the important role of excess surface electrons in the behavior of supported metal catalysts on reducible oxides.