Roles of each composition and strongly-adsorbed NH3 in the formation and depression of N2O in selective catalytic reduction of NO by NH3 (NH3-SCR) with unpromoted and Fe2O3-promoted V2O5/TiO2-based catalysts were intensively studied. V2O5 was found to be active in N2O production at high temperatures while Fe2O3 exhibited a depressive effect. N2O reduction with NH3 and in situ N2O TPSR (temperature programmed surface reaction) measurements indicate that the Fe2O3-promoted catalysts could allow a successful reduction of N2O by strongly-adsorbed surface NH3 species. In situ diffuse reflectance infrared Fourier-transformation spectroscopy (DRIFTS) measurements disclose the presence of strongly-adsorbed NH3 species which were not desorbed even at 500 degrees C and these species could readily react with gaseous N2O at temperatures > 300 degrees C. X-ray photoelectron spectroscopy (XPS) results suggest a charge transfer from V to Fe, which may play a role in decreasing N2O formation at high temperatures. Based on these results, a reaction between N2O and strongly-adsorbed NH3 on Fe2O3 and/or Fe2O3-adjacent VOx species is proposed to be a main pathway for the depression of N2O formation in NH3-SCR reaction with the promoted catalysts.