Periodic density functional theory studies of the VO_x/TiO_2 (anatase) catalysts:Structure and stability of monomeric species

摘要

Periodic density functional theory has been utilized to investigate the structure and stability of monomeric HVO_X species on anatase support. The three most stable surfaces of anatase were investigated, namely the (001), (100) and (101) surfaces. Unlike previous theoretical studies it was found that on the (001) surface vanadia species with five-coordinated vanadium atom are more stable than those with tetrahedrally coordinated vanadium atom. On the other hand, on the (100) and (101) surfaces, the vanadium atom in the vanadia species is still tetrahedrally coordinated. The stability of different VO_X/TiO_2 structures which are not fully dehydrated has been systematically studied and the results show that the vanadia species on the three surfaces follow an order of TiO_2 (001) >TiO_2 (100) >TiO_2 (101). This can be understood from the acidity and basicity of the three anatase surfaces. The results suggest that monomeric VO_X species may be better stabilized if the support exposes more (001) surfaces. Our analyses on electronic structure of the most stable VO_X/TiO_2 structure (D_(001)) suggest that its bridging V-O-Ti oxygen atoms may have higher reactivity than the terminal vanadyl oxygen atoms.