Effect of Ce metal modification on the hydrothermal stability of Cu-SAPO-34 catalyst

Abstract

A series of copper-cerium composite oxide molecular sieve catalysts (Cu-Ce/SAPO-34) were prepared by impregnation method, and the effects of Ce loading on the hydrothermal stability of Cu/SAPO-34 catalyst were discussed. The reasons for the difference in activity and stability of different catalysts were analyzed by XRD, SEM, H2-TPR, XPS, and NH3-TPD. The present studyshowed that hydrothermal aging at 750°C did not cause the chabazite (CHA) framework of Cu-Ce/SAPO-34 catalyst to collapse, but destroyed part of the pore structure and acid sites, and reduced the crystallinity of the catalyst surface. Hydrothermal aging promoted tensile distortion of the catalyst lattice, causing Cu2+ to migrate to the catalyst surface, and Cu2+ and Ce4+ clustered to form CuO and CeO2, which resulted in the reduction of the Cu active species and the decrease of the oxygen hole concentration of the catalyst. Therefore, the performance of Cu-Ce/SAPO-34 for the selective catalytic reduction of NOx by NH3 (NH3-SCR) decreased. Ce doping could increase the amount of Cu2+ and Cu+ active species on the surface of Cu/SAPO-34 catalyst, reduce Cu species clusters to form CuO, and improve the distribution of active Cu species on the catalyst surface. Increasing the loading of Ce could stabilize the structure of Cu-Ce/SAPO-34 catalyst and maintain themedium and weak acid sites, thereby improving its hydrothermal stability. The results indicated that the Cu/Ce mass ratio of 4:5 had the best hydrothermal stability among the series of Cu-Ce/SAPO-34 catalysts in this study.