Quantitative study of the NH3-SCR pathway and the active site distribution over CeWOx at low temperatures

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.