V2O5/AC has been reported to be active for selective catalytic reduction (SCR) of NO with NH3 at around 200 degrees C and resistant to SO2 deactivation. To elucidate its SCR mechanism, adsorption and oxidation of NH3 over V2O5/AC are studied in this paper using TG, MS and DRIFTS techniques. It is found that the adsorption and oxidation of NH3 take place mainly at V=O bond of V2O5. A higher V2O5 loading results in more NH3 adsorption on the catalyst. V2O5 contains both Bronsted and Lewis acid sites; NH4+ on Bronsted acid sites is less stable and easier to be oxidized than NH3 on Lewis acid sites. Gaseous O-2 promotes interaction of NH3 with AC and oxidation of NH3 over V2O5/AC. NH3 is oxidized into NH2 and acylamide structures and then to isocyanate species, which is an intermediate for N-2 formation. (C) 2009 Elsevier B.V. All rights reserved.