Isolated Molybdenum(VI) and Tungsten(VI) Oxide Species on Partly Dehydroxylated Silica: A Computational Perspective

Abstract

Although silica-supported molybdenum and tungsten oxide systems are widely used in catalysis, the nature of the surface metal oxide species is still not fully recognized. In this work, comprehensive periodic and cluster density functional theory (DFT) studies of the isolated Mo(VI) and W(VI) oxide species on dehydrated amorphous silica have been performed to give insight into their heterogeneity. It is shown that the relative stabilities of the metal oxide species strongly depend on their location that influences their geometry and the strain of the dehydrated silica surface. The favorable located monooxo W(VI) species are clearly more stable than the dioxo W(VI) species, whereas no strong thermodynamic preference is predicted in the case of the Mo(VI) species. The relative stability of the monoxo species increases in the order: Cr < Mo