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

An investigation of the influence of support on the activity of monola yer vanadia-titania catalysts in selective catalytic reduction (SCR) o f NO by ammonia has been carried out. The V2O5-TiO2 catalysts were pre pared via VOCI3 grafting on the TiO2 surface, V2O5-WO3-TiO2 catalysts were prepared by inserting ammonium salts in TiO2. The supports and ca talysts were characterized by XPS, XRD, EPR, SIMS, electric conductivi ty, DRS UV-vis, BET, ICP, and X-ray fluorescence methods. The catalyti c activity of samples was determined in a flow recycle reactor. On the basis of catalytic activity data it may be concluded that the specifi c activity, activation energy, and turnover frequency do not depend on the crystal structure of titania. The activation energy of the SCR pr ocess coincides with the vanadia reoxidation activation energy. Reoxid ation 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 proceed s on two surface vanadium atoms. Part of the supported vanadia penetra tes into the sublayers of titania independent of the vanadia introduct ion method and titania crystal structure. (C) 1995 Academic Press, Inc .