The reaction and adsorption amounts of NO, NO2, and NH3 and the reaction pathway of the selective catalytic reduction of NOx with NH3 (NH3-SCR) at low temperatures in the absence and presence of H2O on CeWOx were quantitatively determined by a transient response method (TRM). The distribution of the active sites was quantitatively determined based on the results of TRM, X-ray photoelectron spectroscopy and temperature programmed desorption. NOx adsorbed on O vacancies and oxidized Ce sites, with surface concentrations of 40-63 and 20 mu mol g(-1) respectively, while NH3 adsorbed on [Ce4+]-OH and W species, at 61-70 and 90-99 mu mol g(-1) respectively. Both the reaction between NO and NH4NO3 to form N-2, H2O and NO2, and reaction between nitrite and NH3 to form N-2 and H2O were present. H2O weakened NH3 adsorption, decreased the adsorption amount at 150 degrees C, and inhibited the reaction between NO and NH4NO3/adsorbed NH3, impeding NH3-SCR on CeWOx. (C) 2018 Elsevier Inc. All rights reserved.