Resource Utilization of the Electrolytic Manganese Residue in Preparation of Low-Temperature deNO _<i>x</i> Catalysts and the Mechanism Study of NH ₃ –SCR Reaction

The emission of nitrogen oxides from industrial furnaces and kilns has led to significant atmospheric pollution, necessitating the development of highly efficient low-temperature denitration catalysts. Moreover, the accumulation of electrolytic manganese residue (EMR) hinders the growth of the manganese industry and poses a serious environmental threat. However, electrolytic manganese residue contains valuable metal elements, including Fe and Mn, which can be utilized in preparation of low-temperature denitration catalysts. In this work, a series of samples were prepared using electrolytic manganese residue as a raw material via leaching oxalic acid solutions of varying concentrations and precipitation with ammonia. And the EMR-OA-0.10 (leached by 0.10 mol/L oxalic acid solution) demonstrated excellent NH 3 –SCR activity and good SO 2 resistance, exceeding 90% NO x conversion during 100 to 250 °C. The characterization results revealed that EMR-OA-0.10 had more Mn–O–Fe active structures, which were found to possess superior NH 3 and NO adsorption properties, more surface active oxygen species, and higher Mn 4+ contents, which promoted the adsorption and activation of reaction species. Density functional theory calculations and in situ DRIFTS experiments revealed that the NH 3 species adsorbed at Fe sites within Mn–O–Fe active structures exhibited a stronger reactivity. Furthermore, Mn–O–Fe structures have shown to activate the chelated bidentate nitrates formed at Mn sites, thereby increasing the quantities and variety of the active nitrates. Ultimately, both Eley–Rideal and Langmuir–Hinshelwood mechanisms were found to coexist on the samples surface, with the Langmuir–Hinshelwood mechanism dominating.