Elucidating the electron confinement effect on CeFeW/ZrO2 catalysts to enhance SO2 resistance in the low temperature NH3-SCR reaction

Abstract

Currently, the inefficiency of the catalysts for NOx removal in the presence of SO2 in NH3-SCR reaction still prevalent. The problem of how to improve the SO2 tolerance at low temperature is still a common direction for researchers to work together. In this work, the CeFeW/ZrO2 catalyst prepared by a two-step hydrothermal method exhibited excellent SO2 resistance and SO2 had basically no impact on the CeFeW/ZrO2 catalyst activity. The superior catalytic performance and SO2 tolerance of CeFeW/ZrO2 catalyst mainly originated from that Ce acted as a functional site to form Ce-O-Fe, which altered the local electronic environment through electron confinement effect, increased the proportion of Fe3+/(Fe2+ + Fe3+) and surface chemisorption oxygen as well as the formation of oxygen vacancies on one hand. On the other hand, Fe sites exhibited excellent SO2 capacity and preferentially reacted with SO2, the metal sulfates Fe2(SO4)3 and FeSO4 restrained the formation and deposition of NH4HSO4 and (NH4)2SO4 on the catalyst surface. Simultaneously, the Ce-O-Fe-SO42− species ensured the electron transfer between Ce and Fe, and the redox properties of the catalyst were remained, thus the L-H mechanism on the CeFeW/ZrO2 catalyst could still be carried out smoothly under the conditions of the presence of SO2. Moreover, DFT calculation confirmed that the adsorption ability of NO, NH3 and O2 was enhanced over CeFeW/ZrO2 catalyst, which resulted in an excellent SO2 tolerance.