THE INFLUENCE OF SUPPORT ON THE ACTIVITY OF MONOLAYER VANADIA-TITANIA CATALYSTS FOR SELECTIVE CATALYTIC REDUCTION OF NO WITH AMMONIA

An investigation of the influence of support on the activity of monolayer vanadia-titania catalysts in selective catalytic reduction (SCR) of NO by ammonia has been carried out. The V2O5-TiO2 catalysts were prepared via VOCI3 grafting on the TiO2 surface, V2O5-WO3-TiO2 catalysts were prepared by inserting ammonium salts in TiO2. The supports and catalysts were characterized by XPS, XRD, EPR, SIMS, electric conductivity, DRS UV-vis, BET, ICP, and X-ray fluorescence methods. The catalytic activity of samples was determined in a flow recycle reactor. On the basis of catalytic activity data it may be concluded that the specific activity, activation energy, and turnover frequency do not depend on the crystal structure of titania. The activation energy of the SCR process coincides with the vanadia reoxidation activation energy. Reoxidation of reduced vanadia species seems to be the rate-limiting step of the SCR process. NO SCR by ammonia with and without oxygen may have a common reaction mechanism. Conversion of one NO(NH3) molecule proceeds on two surface vanadium atoms. Part of the supported vanadia penetrates into the sublayers of titania independent of the vanadia introduction method and titania crystal structure. (C) 1995 Academic Press, Inc.