Synergistic Mechanism of Fe-Ce-Mn Ternary Oxides for Wide-Temperature NH3-SCR

Conventional V2O5-WO3/TiO2 catalysts for NH3-SCR suffer from poor low temperature activity, limited thermal stability, and toxicity associated with vanadium, which restrict their application under flexible operating conditions. In this work, a series of Fe-Ce-Mn ternary oxide catalysts were synthesized by a sol-gel route and evaluated for the NH3-SCR of NO in the temperature range of 150 to 400℃. The optimized composition Fe0.1Ce0.04Mn0.02 delivers more than 90 percent NO conversion between 150 and 350℃, while maintaining N2 selectivity above 80 percent even at elevated space velocity and under varied O2 concentrations and NH3/NO feed ratios, indicating excellent tolerance to operating fluctuations. Structural and surface characterizations reveal uniformly distributed Fe, Ce, and Mn species, a high specific surface area of about 160 m2·g-1, and a mesoporous network dominated by 4 to 5 nm pores, together with enriched surface adsorbed oxygen (Oα) and highly oxidized Fe3+/Ce4+/Mn4+ species. It synergizes with acidic sites to provide the surface chemistry foundation for NH3 adsorption activation and NOx surface conversion. In situ DRIFTS coupled with NH3-TPD, NO-TPD, and DFT calculations reveal that NH3 preferentially adsorbs onto Lewis acid sites and undergoes deprotonation to form surface *NH2 species, while NO is converted into monodentate and bridging nitrate species via migratory surface adsorbed oxygen species. These nitrogen containing intermediates coexist isothermally within the 150–350℃ range and undergo in situ coupling via the key NH2NO intermediate, ultimately yielding N2 and H2O. Mn incorporation increases the density of electronic states near the Fermi level and significantly lowers the energy barriers for NH3 dehydrogenation and NH2 nitrate coupling, Gibbs free energy analysis indicates that the key step in this primary pathway is thermodynamically more favorable (with a lower ΔG), while the electronic structure (PDOS) reveals that charge transfer at the interface occurs more readily. Together, these findings collectively support this dominant reaction pathway. This study provides a rational design strategy for vanadium free NH3-SCR catalysts with broad temperature window activity.