Ab Initio Studies of Anatase TiO2 (101) Surface-supported Au-8 Clusters

摘要

Supported transition metals on TiO2 surfaces have shown exceptional catalytic properties in many important process such as CO oxidation, selective propane oxidation, hydrogenation, water adsorption and other catalytic and photocatalytic oxidation reaction at low-temperature. Among the three polymorphs of TiO2, the anatase crystal is the more photoactive. The anatase (101) surface attracts more attention since it has lower surface energy relative to (001) and (100) surfaces and it is observed to adsorb small molecules on its surface. Using density-functional theory (DFT) with on-site Coulomb interactions corrections, we have computed the structural and electronic properties of selected Au-8 clusters interacting with clean and reduced anatase TiO2(101) surfaces. The computed adsorption energies are suggesting that the considered Au-8 clusters are only physisorbed onto pristine TiO2(101) surface. Oxygen vacancies are found to enhance the absorption of Au-8 on the TiO2(101) surface. Accurate simulations required spin polarized DFT since the ground state of Au-8 interacting with defective TiO2(101) shows magnetic solutions. The results show that Au-8 clusters are chemically bonded to the surface around the locality of the oxygen vacancy. The surface oxygen vacancy is found to be energetically more favourable than sub-surface oxygen vacancy configuration. These vacancy sites may act as nucleation sites for small Au clusters or Au atoms. Finally, the computed electronic structure of all the Au-8/TiO2(101) configurations considered in this work are analysed in the light of available experimental data.