Granular CuO/γ-Al2O3 catalysts were synthesized by the sol-gel method.The performance of CuO/γ-Al2O3 catalysts for selective catalytic reduction（SCR）was analyzed in a fixed bed adsorption system.The optimum temperature range for SCR reaction on CuO/γ-Al2O3 catalyst was 250—450℃.Based on the previous study，CuO/γ-Al2O3 catalysts were investigated with in-situ diffuse reflectance infrared fourier transform spectroscopy（DRIFTS）for revealing the reaction mechanism.The DRIFTS indicated both coordinated NH3 and NH+4 were present on the catalysts.NO and NO2 could be adsorbed on the catalyst surface and produce a number of different transformation species.Formation of NO-3 after O2 addition suggested the oxidation of adsorbed NO species to nitrates.When NO was introduced into the samples with pre-adsorbed NH3+O2，the coordinated NH3 on the catalyst surface was consumed rapidly.But NH+4 was not consumed under the SCR reaction.It indicated that these coordinated NH3 species could react with NO effectively.When NH3 was introduced into the samples with pre-adsorbed NO+O2，the intensity of adsorbed NO species did not change; it inferred that SCR reaction would not proceed.It was found that the SCR reaction could take place between the adsorbed NH3 and gaseous NO.The adsorbed NO and formed NO-2 and NO-3 species did not participate in the SCR reaction.