Oxidation state of oxide supported nanometric gold

We address the structure gap between surface science and catalysis studies of the activity of oxide supported An clusters. Reviewing the recent literature we find that surface science investigations often deal with highly reduced systems that have anionic An clusters and oxygen vacancies in the support. The catalysis studies on the other hand consistently report on oxidized samples with traces of cationic An. Performing density functional theory calculations we show that the effect of oxidation of oxide supported An clusters, Au-8/MgO, Au-7/TiO2 and Au-10/TiO2, is a strong increase in the Au/support adhesion energy and a great structural transformation of the clusters. Some of the An atoms become positively charged (cationic) in the oxidation process as evidenced indirectly by calculated vibrational stretch frequency shifts of adsorbed CO.