Role of Au+ in supporting and activating Au7 on TiO2(110)

The adhesion properties and catalytic activity of rutile TiO2(110)-supported Au-7 nanoclusters in different oxidation states are investigated by means of density functional theory. The calculations cover both surface science conditions of reduced TiO2 and real catalyst conditions of oxidized (alkaline) TiO2 supports. Large adhesion energies of Au-7 are found only when modeling real catalysts where the cluster becomes cationic with Au+ ions in Au-O or Au-OH bonds. The full catalytic cycle for oxidation of CO by O-2 over Au-7 on alkaline TiO2(110) is calculated and found to involve only small activation barriers. In the presence of the CO reductant, the Au+ sites are capable of cycling between bonding of atomic and molecular oxygen. We confirm our findings by comparison of calculated and experimental infrared stretch frequency data for adsorbed CO.