Mechanistic investigation of Sm doping effects on SO2 resistance of W-Zr-ZSM-5 catalyst for NH3-SCR

The WO3-ZrO2 for NH3-SCR catalyst has excellent NO conversion, especially at high temperature, which are appropriate for the diesel engine after-treatment system. However, the diesel engine NH3-SCR catalysts can be affected by SO2 toxicity. Thus, a series of xSm-WZZ catalysts were prepared by sol–gel method, and the Sm species as the promoter were applied to enhancing the SO2 resistance and regeneration performance of the catalyst. 1Sm-WZZ catalyst exhibited the best SO2 and H2O resistance and slightly improved the NH3-SCR activity, in which 100% NO conversion and N2 selectivity can be achieved at 400–600 ℃. Moreover, compared with WZZ catalyst, 1Sm-WZZ catalyst showed excellent regeneration performance, which could be regenerated by thermal treatment at 350 ℃. The results of XPS, CO2-TPD and H2-TPR revealed that the Sm could decrease the amount of alkaline sites and redox ability of catalyst, which may be the main reason for the reduction of the adsorption and oxidation of SO2. Additionally, the Sm decreased the formation of ammonium sulfate salts on catalyst, which were verified by the TGA and FTIR spectrum experiments. Furthermore, the Sm could preferentially react with SO2 than chemisorbed oxygen, which restrains the reaction of chemisorbed oxygen with SO2, thereby reducing the generation of sulfate around the chemisorbed oxygen. In addition, the in-situ DRIFTS tests indicated that the Sm could reduce the generation of S = O for tridentate sulfate species and SO3 on the catalyst.