Effect of Co–Mn combined modification of rare earth tailing catalyst on denitrification performance of NH3-SCR

As a natural mineral, Bayan Obo rare earth tailings are an environmentally friendly and cost-effective. They contain Fe, Ce, Nb and other active elements that facilitate catalytic denitrification, with Fe and Ce exhibiting pronounced synergistic effects due to their complex co-occurrence relationships. In this study, we developed a catalyst by using Bayan Obo rare earth tailings as a carrier and incorporating small amounts of Co and Mn as active components. The influence of these additives was systematically investigated, focusing on denitrification performance, pore structure, surface acidity redox properties and elemental valence states. The catalysts were characterized through XRD, SEM, BET, NH₃-TPD and H₂-TPR. Results demonstrated that the Co–Mn (3%,4%)-modified rare earth tailings achieved 95% denitrification efficiency within a low-temperature range of 150–300 °C. Co–Mn co-doping increased the specific surface area, with the 5%Mn-2.5%Co-modified catalyst exhibiting optimal structural parameters (75.3188 m²/g surface area and 10.2179 nm pore diameter). Furthermore, the addition of Co and Mn enhanced surface acidity, as evidenced by a pronounced weak acid desorption peak in NH₃-TPD, which promoted low-temperature activity. Redox capacity analysis revealed that Mn doping concentration positively correlated with catalytic redox potential. Co incorporation further amplified this effect by stabilizing low-valent MnO_x species (e.g., Mn³⁺), thereby suppressing MnO₂ over-oxidation and minimizing undesirable NH₃ oxidation via Mn₂O₃ inhibition.