## 3 Binary Mn-Based Metal Oxide Catalysts
### Other Binary Mn-Based Metal Oxide Catalysts
[63] developed a new Mn-Zr mixed oxide catalyst through the citric acid method for the SCR of NO\({}_{\mathrm{x}}\) using ammonia at low temperatures in excess oxygen. Characterization indicated that the Mn (0.5)-ZrO\({}_{\mathrm{x}}\)-450 catalyst, with a Mn/(Mn + Zr) molar ratio of 0.5, has the highest activity. At 100 \({}^{\circ}\)C and a space velocity of 30,000 h\({}^{-1}\), the NOx conversion rate reaches 100%. XRD results indicated the formation of a Mn-Zr solid solution in the Mn (0.5)-ZrO\({}_{\mathrm{x}}\)-450 catalyst and high dispersion of MnO\({}_{\mathrm{x}}\). TPR data revealed a strong interaction between zirconia and manganese oxide, enhancing MnO\({}_{\mathrm{x}}\)'s reduction ability. TPD results showed that an appropriate NH\({}_{3}\) adsorption capacity benefits low-temperatureSCR operation. The catalyst demonstrates specific sulfur and water resistance; the effect of H\({}_{2}\)O can be quickly eliminated after removal, while SO\({}_{2}\) deactivation was found to be irreversible. Zhang et al. [42] prepared MnxZr1 series catalysts via the co-precipitation method to study the effect of zirconium doping on the NH\({}_{3}\)-SCR performance of the MnO\({}_{\mathrm{x}}\) catalyst. The results indicated that the Mn\({}_{6}\)Zr\({}_{1}\) catalyst, when calcined at 400 \({}^{\circ}\)C, exhibits excellent NH\({}_{3}\)-SCR activity. With a reaction temperature range of 125-250 \({}^{\circ}\)C, the NOx conversion of the Mn\({}_{6}\)Zr\({}_{1}\) catalyst exceeds 90%, reaching an optimal conversion efficiency of 97%. Additionally, the Mn\({}_{6}\)Zr\({}_{1}\) catalyst exhibits excellent SO\({}_{2}\) and H\({}_{2}\)O resistance at the optimal reaction temperature. Characterization results demonstrated significant changes in the morphology of the MnO\({}_{\mathrm{x}}\) catalyst and improved physical properties with the increased Mn\({}^{4+}\) and O\({}_{\mathrm{a}}\) component ratio. Moreover, the Mn\({}_{6}\)Zr\({}_{1}\) catalyst contains both Lewis and Bronsted acid sites, which lowers the reduction temperature of the catalyst. Er doping enhances the surface acid sites, increases the surface adsorbed oxygen of the MnO\({}_{\mathrm{x}}\) catalyst, and improves the redox performance. Fang et al. [43] synthesized various Er-modified MnO\({}_{\mathrm{x}}\) catalysts using the co-precipitation method and performed NH\({}_{3}\)-SCR of NOx testing. Employing different characterization techniques, they found that Er doping can significantly improve the catalytic performance of the MnO\({}_{\mathrm{x}}\) catalyst. MnEr\({}_{0.1}\) exhibits a superior catalytic performance in the NH\({}_{3}\)-SCR reaction due to its abundant surface acidic sites, high Mn\({}^{4+}\) surface content, excellent redox performance, and increased surface adsorbed oxygen. Ni doping can effectively adjust the surface lattice oxygen activity of the MnO\({}_{\mathrm{x}}\) catalyst, as well as the surface concentration and acidity of Lewis acid sites, ensuring the NH\({}_{3}\) activation ability of the catalyst at low temperatures. Concurrently, the catalyst's resistance to SO\({}_{2}\) is significantly improved. Ni-doped MnO\({}_{\mathrm{x}}\) catalysts (NMOs) prepared by Kang et al. [64] using a solvent-free doping method demonstrated excellent performance over a wide temperature range of 100-300 \({}^{\circ}\)C in SCR. The effect of Ni loading on NH\({}_{3}\)-SCR activity at medium temperatures (200-300 \({}^{\circ}\)C) was investigated. The NMOs-4 catalyst not only maintains an excellent low-temperature (100-200 \({}^{\circ}\)C) NH\({}_{3}\)-SCR activity with a nearly 100% NO conversion rate, but also at 300 \({}^{\circ}\)C (T\({}_{95}\) = 100-265 \({}^{\circ}\)C), compared to the undoped MOs catalyst (T\({}_{95}\) = 100-225 \({}^{\circ}\)C), the NO conversion rate increases from 54.4% to 87.2%, significantly improving the medium-temperature activity.