The sulfation showed a dual effect on the selective catalytic reduction (SCR) reaction over MnOx/TiO2. The activation of adsorbed NH3 and the adsorption of NO on MnOx/TiO2 were both restrained after the sulfation. Therefore, the SCR reaction through the Eley-Rideal mechanism and that through the Langmuir-Hinshelwood mechanism were both restrained, resulting in an obvious decrease of NO conversion below 300 degrees C. During NO reduction over MnOx/TiO2 at higher temperatures, there was a competition among the SCR reaction, the nonselective catalytic reduction (NSCR) reaction and the catalytic oxidation of NH3 to NO. The NSCR reaction and the catalytic oxidation of NH3 to NO over MnOx/TiO2 at higher temperatures were both restrained after the sulfation, so more NH3 adsorbed on sulfated MnOx/TiO2 was used to reduce NO to N-2. Therefore, the SCR activity and N-2 selectivity of sulfated MnOx/TiO2 at higher temperatures were much higher than those of MnOx/TiO2.