SURFACE AND CATALYTIC PROPERTIES OF VANADIA-TITANIA AND TUNGSTA-TITANIA SYSTEMS IN THE SELECTIVE CATALYTIC REDUCTION OF NITROGEN-OXIDES

The chemistry of the Selective Catalytic Reduction (SCR) of NO(X) with ammonia over V2O5-TiO2 and WO3-TiO2 catalysts has been investigated by Fourier-Transform Infrared spectroscopy, Temperature Programmed Desorption, Temperature Programmed Surface Reaction and catalytic activity measurements. Protonated and molecularly coordinated ammonia species, associated with Bronsted and Lewis acid sites respectively and with different thermal stability, are observed upon NH3 adsorption. WO3-TiO2 show stronger Lewis and Bronsted acid sites than V2O5-TiO2. Upon heating in NO atmosphere, a reaction between adsorbed ammonia and gas-phase or weakly adsorbed NO is monitored by FT-IR and TPSR measurements. The results indicate that V2O5-TiO2 is significantly more active than WO3-TiO2 due to its superior redox properties. Monomeric vanadyls and meta-vanadate polymers are proposed as the active sites in the SCR reaction, the former sites showing lower reactivity. Oxygen is involved in the reaction and plays a crucial role in determining the reactivity of,the catalysts.