Defect Engineering of Ce-Modified Mullite Oxide Nanostructures for Low-Temperature Selective Catalytic Oxidation of NH ₃ to N ₂

A high surface area Ce-modified YMn2O5–CeO2 mixed oxide (YCMO) catalyst, featuring nanoscale phase dispersion, was prepared via a facile hydrothermal approach. The introduction of Ce suppressed further mullite phase formation and generated abundant oxygen vacancies and modulated the redox properties of Mn sites. The resulting nanoscale interfacial structure facilitates oxygen activation and transfer, leading to superior low-temperature NH3 oxidation performance. The YCMO achieved 90% NH3 conversion (T90) at 160 °C under a GHSV of 100,000 h–1 with 500 ppm of NH3 and 21% O2 in N2, approximately 29 °C lower than YMn2O5 (YMO) and 62 °C lower than commercial 1% Pt/Al2O3, while maintaining stable N2 selectivity across a broad temperature range (160–236 °C). Combined XRD, TEM, and O2-TPD analyses confirm the coexistence of finely dispersed CeO2 and YMn2O5 nanophases, which synergistically enhance surface oxygen mobility. Fundamentally, the exceptional performance arises from CeO2’s role as an oxygen reservoir, supplying reactive oxygen species that enable rapid NH3 deep oxidation and diverse nitrate intermediate formation via the internal SCR (i-SCR) mechanism, coupled with their facile thermal desorption to prevent deactivation. In situ DRIFTS revealed that bridged and bidentate nitrates exhibit high thermal sensitivity, desorbing readily without intermediate accumulation, thus sustaining efficient active-site regeneration. This work demonstrates that nanoscale engineering of mixed oxides is an effective strategy to improve low-temperature catalytic activity and stability in NH3–SCO systems.