Adsorption of gold subnano-structures on a magnetite(111) surface and their interaction with CO

Abstract

Gold deposited on iron oxide surfaces can catalyze the oxidation of carbon monoxide. The adsorption of gold subnano-structures on the Fe-rich termination of the magnetite(111) surface has been investigated using density functional theory. The structural, energetic, and electronic properties of gold/magnetite systems have been examined for vertical and flattened configurations of adsorbed Au_n (n = 1–4) species. Single gold adatoms strongly bonded to the iron atoms of the Fe₃O₄(111) surface appear to be negatively charged, and consequently increase the work function. For a more stable class of larger, flattened Au_n structures the adsorption binding energy per adatom is substantially increased. The structures exhibit a net positive charge, with the Au atoms binding with the oxide having distinctly cationic character. A charge transfer from the larger gold structures to the substrate is consistent with the lowering of the work function. The bonding of a CO molecule to a Au monomer on the Fe₃O₄(111) surface has been found nearly as strong as that to the iron site of the bare Fe-terminated surface. However, CO bonding to larger, oxide supported Au_n structures is distinctly stronger than that to the bare oxide surface. Upon CO adsorption all Au_n structures are cationic and CO shows a tendency to bind to the most cationic atom of the Au_n cluster.