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

Efficiently reducing nitrogen oxides (NOx) 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, Fe0.57-Mn0.43-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.