The role of tungsten in formation of active sites for no SCR on the V-W-O catalyst surface — quantum chemical modeling (DFT)

Abstract

This study concerns quantum chemical modeling of water behavior on basal surface of WO 3–V 2O 5 solid solution crystallites with V 2O 5 structure. It was undertaken in order to validate the hypothesis that the presence of W atoms in vanadia-like surface species of V-W-O catalysts facilitates low temperature water dissociation leading to formation of OH groups being active sites in selective NO x reduction by ammonia. Quantum chemical calculations were done with the use of modern electronic structure methodology based on the density functional theory (DFT). The calculations were performed for small clusters representing two adjacent metal sites in pentacoordinated oxygen environment, analogous to bipiramidal clusters introduced in description of the basal face of vanadium pentoxide. The results indicate that adsorption of water strongly depends on the presence of tungsten atom at the surface. Dissociative water adsorption leading to Bronsted acid centers creation is promoted. The proton acidity of the centers decreases with the increase of tungsten concentration in V 2O 5 matrix leading to the increase of V 4+W 6+/V 5+W 6+ ratio.