Mn/Fe synergy enables wide-temperature NH3-SCR activity over MnFeCe/SSZ-13: insights into the structure-activity relationship.

The selective catalytic reduction of NO x with ammonia (NH3-SCR) is a key technology for abating NO x emissions. Single-metal-loaded zeolite catalysts typically exhibit inferior low-temperature activity and a narrow effective temperature window, and the unclear synergistic mechanisms among multiple metal components further hinder their practical application. Herein, we synthesized a series of MnFeCe/SSZ-13 catalysts with varying Mn/Fe mass ratios using a wet chemical ion-exchange method to enhance low-temperature activity and expand the active temperature range. The optimal Mn(6 wt%)Fe(2 wt%)Ce-13 catalyst achieved >90% NO conversion over a temperature range of 185-475 °C, representing a 160 °C shift toward lower temperatures compared with the Fe(8 wt%)Ce-13. Systematic characterization revealed that a suitable Mn/Fe ratio facilitated the formation of abundant surface Mn4+/Fe2+ species and a high content of surface-adsorbed oxygen. In this synergistic system, Mn4+ promotes NO oxidation to NO2, contributing to the fast SCR pathway; Fe2+ inhibits NH3 over-oxidation at high temperatures; and Ce4+ may acts as an oxygen buffer to stabilize the catalytic cycle. In situ DRIFTS further provided evidence for the coexistence of Langmuir-Hinshelwood (L-H) and Eley-Rideal (E-R) mechanisms along with fast selective catalytic reduction (fast SCR) reaction. This work unravels the Mn-Fe synergistic mechanism that addresses the issues of insufficient low-temperature activity and restricted temperature range, offering experimental validation and mechanistic guidance for developing high-performance NH3-SCR catalysts with extended temperature applicability.