Disentangling Site-Selective Redox Couples for N2O Activation on Fe-Exchanged SSZ-13 Using Modulated Excitation Operando EPR spectroscopy

Iron-exchanged zeolites are promising materials for mitigating N2O emissions and converting methane into methanol. Here, we present site-specific kinetic analysis of N2O decomposition over Fe-SSZ13 under inert conditions and utilizing reducing agents (CH4, NH3, H2). Operando EPR measurements with phase-sensitive detection proved essential for distinguishing active sites from spectator species during reactions. The time resolution was further enhanced by using an EPR step-scan methodology. Isolated Fe2+ centers in axial coordination contribute solely to N2O decomposition without reducing agents, while FexOy clusters and Fe2+ sites in distorted geometries show redox activity when present. Quantitative kinetic analysis reveals that, in the presence of CH4, H2, and under autocatalytic conditions, the reduction half-cycle, whereas with NH3, the oxidation half-cycle is rate-limiting.