Small gold clusters on stoichiometric and defected TiO2 anatase (101) and their interaction with CO: A density functional study

We have studied the interaction of small Aun (n=1–3) particles with the defect-free (stoichiometric) and defected (partially reduced) TiO2 anatase (101) surface using density functional calculations within a slab geometry. On the stoichiometric surface, gold particles prefer anion sites and “standing” geometries, in agreement with simple MO theory arguments. On the defected surface, Au strongly binds to the two cations close to the bridging oxygen vacancy. For both Au2 and Au3, “lying” adsorption geometries are now more likely, and starting from n=3 there is a tendency towards mixed binding, where cation and anion sites are simultaneously involved. Clustering of Au atoms is favored on both the stoichiometric and the reduced surfaces. CO strongly interacts with gold particles adsorbed on the stoichiometric surface. As found in previous gas-phase investigations, the CO-cluster bond is stronger when the cluster carries a positive charge. Accordingly, a weak interaction is computed for a gold atom supported on the reduced surface.