Low-Temperature NH ₃ –SCR over Pr-Modified Mn–Fe Oxides: Widened Activity Window and Enhanced SO ₂ and H ₂ O Tolerance

Pr-modified Mn–Fe mixed oxides were synthesized via a solvothermal method and systematically characterized (Brunauer–Emmett–Teller (BET), X-ray diffraction (XRD), Field emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), NH3-TPD, H2-TPR, O2-TPD, Py-IR, Raman spectroscopy, and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS)). At a Pr/Mn molar ratio of 0.1, MnFePr0.1Ox achieved a high NOx conversion from 90 to 300 °C at GHSV = 50,000 h–1(>94%). MnFePr0.1Ox N2 selectivity decreased from 98% at 90 °C to 72% at 270 °C, and it remained 6–10% higher than that of MnFe0.7Ox across the temperature range. Under 50 ppm of SO2 and 10 vol % H2O at 150 °C, MnFePr0.1Ox maintained high activity (>99%) for 10 h, while MnFe0.7Ox deactivated to 30%. The enhanced performance is attributed to the enrichment of Mn4+ and surface-adsorbed oxygen and a regulated acidity with redistributed acid-site characteristics. In situ DRIFTS revealed coexisting Langmuir–Hinshelwood and Eley–Rideal mechanisms. Pr incorporation further enhanced NOx adsorption and stabilized surface NH3 species, suggesting robust cooperative reactivity under SO2 and H2O exposure.