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

This study concerns quantum chemical modeling of water behavior on basal su rface of WO3-V2O5 solid solution crystallites with V2O5 structure. If was u ndertaken in order to validate the hypothesis that the presence of W atoms in vanadia-like surface species of V-W-O catalysts facilitates low temperat ure water dissociation leading to formation of OH groups being active sites in selective NO, reduction by ammonia. Quantum chemical calculations were done with the use of modern electronic structure methodology based on the d ensity functional theory (DFT). The calculations were performed for small c lusters representing two adjacent metal sites in pentacoordinated oxygen en vironment, analogous to bipiramidal clusters introduced in description of t he basal face of vanadium pentoxide. The results indicate that adsorption o f water strongly depends on the presence of tungsten atom at the surface. D issociative water adsorption leading to Bronsted acid centers creation is p romoted. The proton acidity of the centers decreases with the increase of t ungsten concentration in V2O5 matrix leading to the increase of V4+W6+/V5+W 6+ ratio. (C) 2001 Elsevier Science B.V, All rights reserved.