Effect of Dispersion State and Surface Properties of Supported Vanadia on the Activity of V2O5/TiO2 Catalysts for the Selective Catalytic Reduction of NO by NH3

The effect of the dispersion state and surface properties of supported vanadia on the selective catalytic reduction (SCR) activity of NO over V2O5/TiO(2)catalysts was studied by various experimental techniques. The experimental monolayer dispersion capacity of V2O5 on anatase (6.86 VOx/nm(2)) measured by XRD was almost the same as the concentration of surface vacant sites of anatase estimated by the incorporation model, and it was suggested that isolated vanadia species tend to be dispersed on adjacent octahedral vacant sites. An increase of the NO turnover frequency (TOF) at 300 degrees C to a maximum (8.3 x 10(-3)s(-1)) at a coverage near half a monolayer was related to the increase of the amount of weak acid sites (Bronsted acid site on each vanadium ion). The TOF decreased rapidly at high VOx, coverages because of a decrease of the reducibility of vanadia species and a decrease of the ratio of exposed vanadia species on the surface. The Bronsted acid sites on bridging V-O(H)-V and terminal V-OH of polymeric vanadia species were all active sites in the SCR reaction. The SCR activity of the V2O5/TiO2 catalysts was related to the dispersion state, acidity, and reducibility of the vanadia species.