Unraveling the significance of acid sites in determining NH3-SCR mechanisms over WO3 catalyst: A combined experimental and computational study

Abstract

With regard to the catalysts for NH3 selective catalytic reduction (NH3-SCR), the acid sites distribution can affect the adsorption of reactants and formation of intermediates, thus determining the reaction routines. In this work, a representative acidic component, monoclinic-WO3 (m-WO3), was used to probe the combination strategy of experimental and theoretical research, aiming at systematic understanding on the full-process mechanisms. Macro-scale characterizations, Temperature Programmed Desorption (TPD) and Temperature Programmed Reduction (TPR), are associated with the Density Functional Theory (DFT) calculations, by which W ion (Lewis acid site) is affirmed as the active sites. By comparing the energy barriers of possible pathways with DFT calculations, we identify that NH2NO and NHNOH are responsible active intermediates. Both Langmuir-Hinshelwood (L-H) and Eley-Rideal (E-R) pathways may take place on acid sites and the former on Lewis acid site is optimal, which agrees well the in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS) analysis. This study offers a reasonable prototype for precisely examining the correlation between the catalyst and mechanisms of NH3-SCR catalysts.