The effect of CO2 and H2O addition on selective catalytic reduction of NO by NH3 (NH3-SCR) over Cu/SAPO-34 catalysts was confirmed and we tried to study their influence in this research. Two Cu/SAPO-34 samples with the equivalent Cu loading were utilized, and their acidities were adjusted by the Si amounts in SAPO-34 supports. NH3-SCR, NH3-TPD, NH3 oxidation and kinetic analysis were conducted to evaluate the role of CO2 and H2O. NH3-SCR results revealed that CO2 in the inlets presented less impact on NO conversion, while the presence of H2O enhanced NO conversion during the whole temperature range. NH3-TPD results showed H2O improved the acidity of Bronsted acid sites and the reducibility of Cu2+ species, both of which benefited the NH3-SCR activity. In addition, the presence of H2O at high temperature inhibited NH3 conversion and side-products during NH3 oxidation process. Kinetic analysis of NH3-SCR and NH3 oxidation at high temperature were further conducted to estimate the variation of apparent activation energy (Ea) for the presence of water vapor, and finally the relation between the variation of acidity, Cu2+ species reducibility and the SCR mechanism over Cu/SAPO-34 sample at different temperature ranges was proposed, respectively. (C) 2014 Elsevier B.V. All rights reserved.