Enhanced low-temperature CO-SCR performance under O₂-rich atmospheres of Fe-doped Mn-MOF-74 Catalyst: Experimental...

Efficiently reducing nitrogen oxides (NO_x) at low temperatures under oxygen-rich conditions is a significant challenge in industrial denitrification. This study synthesized a series of bimetallic MOF-74 catalysts through a one-step hydrothermal method using cost-effective transition metals. Screening indicated that the inclusion of Fe notably improved the specific surface area, optimized the Mn³⁺/Fe²⁺ redox cycle, and generated synergistic Fe-Mn oxygen vacancies, enhancing Lewis acid sites and oxygen mobility. Particularly, Fe_0.57-Mn_0.43-MOF-74 demonstrated over 90 % NO conversion and N₂ selectivity at 250 °C under 2 %-6 % oxygen-rich conditions, displaying 2.31 and 1.56-fold enhancements in oxygen tolerance compared to single-metal Mn-MOF-74 and Fe-MOF-74 catalysts, respectively. In-situ FTIR and DFT analyses revealed that NO reduction proceeded through the ONNO pathway with the lowest energy barrier under anaerobic conditions, facilitated by adsorbed CO promoting ONNO∗ dissociation into ONN∗, which further decomposed into N₂. Conversely, under oxygen-rich conditions, the Fe-Mn synergistic oxygen vacancy structure trapped O₂ to form chemisorbed oxygen species, steering the reaction pathway towards N₂O₂ intermediates with the lowest energy barrier. Adsorbed CO induced N₂O₂∗ dissociation into ONNO∗, leading to decomposition into ONN∗ and ultimately N₂. This investigation offers a viable approach for designing highly effective and sustainable catalysts for industrial denitrification under oxygen-rich conditions.