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 NH₃-SCR activity and good SO₂ resistance, exceeding 90% NO_<i>x</i> 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 NH₃ and NO adsorption properties, more surface active oxygen species, and higher Mn⁴⁺ contents, which promoted the adsorption and activation of reaction species. Density functional theory calculations and in situ DRIFTS experiments revealed that the NH₃ 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.