Resource utilization of red mud to construct Mn/N biochar–coupled catalysts with superior low-temperature denitration performance

A high-performance and poison-resistant low-temperature NH₃-SCR catalyst was developed by coupling acid-roasted red mud with Mn/N biochar (1:4 coupled sample). This new catalyst maintains good stability with NO conversion rate of over 90% in the temperature range of 125–250 °C. A combination of characterization, in-situ DRIFTS, and DFT calculations demonstrates that its superior performance originates from the synergistic effects at the Fe₂O₃/MnO₂ interface: (i) The optimized mesoporous structure and abundant Mn-O-Fe interfaces promoted mass transfer and reaction; (ii) Interfacial electron coupling induces a high concentration of surface-adsorbed oxygen and high-valence Mn⁴⁺/Fe³⁺ species, significantly enhancing the redox capability; (iii) Balanced surface acidity and the synergistic operation of both E-R and L-H reaction pathways ensure an efficient catalytic cycle across the wide temperature range. Furthermore, the DFT calculations and experimental results revealed that SO₂ was preferentially adsorbed on Fe sites (“Fe sacrificial adsorption”), protecting Mn active centers. Meanwhile, the moderately adsorbed H₂O causes reversible competitive inhibition during the reaction but acts as a “trigger switch” after gas cut-off: its preferential desorption promotes the simultaneous desorption of SO₂, enabling rapid and complete recovery of catalytic activity. XPS and EDS analyses confirm that H₂O suppresses the formation of stable metal sulfates, favoring the deposition of more readily removable ammonium sulfates. This work provides a reference for the efficient design of red mud-based and Mn-based denitration catalysts.