Paper SS2-TuM12
Theoretical Prediction of Ordering and Reactivity of Bimetallic Gold Alloy Surfaces

Tuesday, November 10, 2009, 11:40 am, Room N

Bimetallic materials have shown great promise for the development of superior catalysts. The recent surge of new interest in catalysis by gold has led researchers to investigate the effects of adding gold to other metals. While mechanisms underlying the alloying effect are still not understood in detail, recent evidence suggests that the enhanced reactivity of bimetallic catalysts can be attributed to a combination of metal-metal interactions (ligand effect) and unique mixed-metal surface sites (ensemble effect). The ability to a ccurately predict the arrangements of constituent atoms in a surface alloy is indispensable to unraveling the roles played by the ensemble and ligand effects i n the performance of bimetallic model catalysts. We might expect that the arrangement of surface and near-surface atoms is a complex function of temperature, stoichiometric ratio, and surface facet, but t hus far, only very limited theoretical effort has been undertaken to determine the atomic distribution of bimetallic alloys. We have developed a scheme to predict the equilibrium arrangement of atoms in surface alloys at finite temperatures. Our scheme is based on the Ising model, and is capable of reproducing DFT-predicted total energies to within no more than a few meV per surface atom. We will present our scheme in detail, as well as what we have learned about the effects of temperature, composition, surface facet, and particle identity on the arrangement of surface atoms for various gold-based binary alloys including gold-palladium and gold-platinum. We will also discuss how the atomic arrangements affect the reactivity of gold-based alloy surfaces particularly towards oxidation of hydrogen and carbon monoxide.