Influence of the V2O5 loading on the structure and activity of V2O5/TiO2 SCR catalysts for vehicle application

In this paper the effect of the vanadium oxide loading on the surface vanadia structure and the activity as well as selectivity in the catalytic reduction of NO with NH3 was studied for a V2O5/TiO2 model system. A series of TiO2 (WOx stabilized anatase) supported vanadia catalysts with varying loadings were characterized by laser Raman spectroscopy, V-51 MAS-NMR, V K XANES. To determine the acidic properties, DRIFTS measurements were done with pyridine adsorbed on the samples. The measurements indicate that with increasing active phase loading square pyramidal coordinated surface vanadia species are replaced by an amorphous highly dispersed vanadium oxide phase with a coordination like V2O5. In addition, the ratio of Bronsted to Lewis acid sites is shifted from a comparatively low to an equal level at high loadings. This structural change is accompanied by a clearly improved catalytic activity and selectivity.