Adsorption, Dissociation, and Spillover of Hydrogen over Au/TiO2 Catalysts: The Effects of Cluster Size and Metal-Support Interaction from DFT

The effects of cluster size and metal-support interaction on the catalytic activity of Au nanoparticles supported on anatase TiO2(101) and (001) surfaces for H-2 adsorption, activation and dissociation were investigated by periodic density functional theory (DFT) calculations. On the stoichiometric TiO2 surfaces, it was found that the adsorptions of both Au clusters and H-2 molecules are sensitive to the cluster size of gold, and the (001) facet with soft lattice and coordination unsaturated atoms on the surface is superior for Au adsorption stability, but H-2 adsorption does not show apparent distinction on the two catalysts. The Au atoms active for H-2 activation should be neutral in charge and located at the edge or corner of the Au nanoparticles in lower coordination. The metal support interaction plays an important role for H-2 activation and dissociation, and the O2--H+-H--Au structure was identified in the transition state through which H-2 dissociation occurred via a heterolytic dissociation process at the Au TiO2 interface for both facets. H* spillover from the Au site to the bridging -O2cH site can generate H2O molecules on the two facets, and O-vacancy formation is energetically more favorable on (101) than (001). The presence of O-vacancy defects significantly impacts the adsorption stability of Au clusters and H-2 molecule but has small effect on the energy barrier for H-2 dissociation, which proceeds fast on both the stoichiometric and reduced anatase TiO2(101) and (001) surfaces.