Mechanistic Insight into the Promotion of the Low-Temperature NH3–SCR Activity over NiMnFeOx LDO Catalysts: A Combined Experimental and DFT Study

Mn-based catalysts have attracted much attention in the field of the low-temperature NH 3 selective catalytic reduction (NH 3 –SCR) of NO. However, their poor SO 2 resistance, low N 2 selectivity, and narrow operation window limit the industrial application of Mn-based oxide catalysts. In this work, NiMnFeO x catalysts were prepared by the layered double hydroxide (LDH)-derived oxide method, and the optimized Ni 0.5 Mn 0.5 Fe 0.5 O x catalyst had the best denitration activity, excellent N 2 selectivity, a wider active temperature range (100–250 °C), higher thermal stability, and better H 2 O and/or SO 2 resistance. A transient reaction revealed that Ni 0.5 Mn 0.5 Fe 0.5 O x inhibited the NH 3 + O 2 + NO x pathway to generate N 2 O, which may be the main reason for its improved N 2 selectivity. Combining experimental measurements and density functional theory (DFT) calculations, we elucidated at the atomic level that sulfated NiMnFeO x (111) induces the adjustment of the acidity/basicity of up and down spins and the ligand field reconfiguration of the Mn sites, which improves the overall reactivity of NiMnFeO x catalysts. This work provides atomic-level insights into the promotion of NH 3 –SCR activity by NiMnFeO x composite oxides, which are important for the practical design of future low-temperature SCR technologies.