The Comparative Study of Reaction Mechanisms and Catalytic Performances of Cu–SSZ-13 and Fe–SSZ-13 for the NH3-SCR Reaction

Abstract

The catalytic performances and mechanism differences of model catalysts Cu–SSZ-13 and Fe–SSZ-13 with similar metal content and Si/Al ratio were compared. In the NH₃-SCR reaction, Cu–SSZ-13 had a good NO conversion at low temperature, broad active temperature windows and better hydrothermal stability. Fe–SSZ-13 showed better high-temperature NO conversion rate and better resistance to sulfur poisoning, but poorer low-temperature NH₃-SCR activity. NH₃-TPD verified the content difference of L-NH₃ and B-NH₃ of Cu- and Fe–SSZ-13. UV–Vis DRS, EPR, H₂-TPR indicated the active species of Cu- and Fe–SSZ-13. Results showed that Cu–SSZ-13 only had one type active species of Cu²⁺, Fe–SSZ-13 had Fe³⁺ species that acted as active centers at low temperature and reactivity oligomeric Fe species at high temperature. The diffuse reflection infrared Fourier transform spectrum (DRIFTS) results showed that the reactions of Cu–SSZ-13 and Fe–SSZ-13 at low temperature both followed the Eley–Rideal (E–R) mechanism and the Langmuir–Hinshelwood (L–H) mechanism. Cu–SSZ-13 could perform the catalytic process well under both mechanisms, but when Fe–SSZ-13 followed the E–R mechanism, there were many B-NH₃ species, which was not conducive to the reaction. When following the L–H mechanism, the speed of NO₃⁻ participating in the reaction was slow due to ammonia inhibition, resulting in poor low-temperature activity.