## 3 Binary Mn-Based Metal Oxide Catalysts
### Other Binary Mn-Based Metal Oxide Catalysts  
To optimize the denitration performance of MnO\({}_{\rm x}\) catalysts and ensure their better adaptation to practical conditions, scholars have attempted to boost surface acidity, redox performance, N\({}_{2}\) selectivity, and resistance to H\({}_{2}\)O and SO\({}_{2}\) poisoning by doping metal oxides such as Fe, Co, Ni, and Sm, Si, and some organic compounds, excluding CeO\({}_{2}\) and TiO\({}_{2}\). Many reports have pointed out that doping MnO\({}_{\rm x}\) catalysts with metal oxides like Pr, In, Cu, Fe, Sm, and Gd can increase the catalyst's specific surface area. Doping metal oxides such as Eu, Cr, Sm, Zr, and Gd helps to prevent the crystallization of MnO\({}_{\rm x}\), thereby ensuring a more effective dispersion of active substances within the catalyst. Doping metal oxides like Er, Ni, Fe, Nb, and V can increase the catalyst's surface acid sites, enhancing its redox performance and N\({}_{2}\) selectivity. Traditional Mn-based catalysts have poor SO\({}_{2}\) poisoning resistance because SO\({}_{2}\) irreversibly reacts with NH\({}_{3}\) on the catalyst's surface, forming a sulfate covering that inhibits the SCR reaction. The doping of metal oxides like Si, Pr, Al, Co, Gd, and Ni to MnO\({}_{\rm x}\) catalysts can inhibit the poisoning of MnO\({}_{2}\) by SO\({}_{2}\) to a certain extent and enhance its SO\({}_{2}\) resistance. Pr modification can improve the specific surface area and dispersion of the catalyst while protecting the active MnO\({}_{\rm x}\) sites in the presence of SO\({}_{2}\), thus boosting the SCR activity and sulfur resistance of the MnO\({}_{\rm x}\) catalyst. Zhai et al. [34] applied the co-precipitation method to modify the MnO\({}_{\rm x}\) catalyst with Pr and investigated the effect of this modification on the SCR performance. The results revealed that the MnPrOx-0.1 catalyst achieves nearly 100% NO conversion efficiency within a temperature range of 120 \({}^{\circ}\)C to 220 \({}^{\circ}\)C, and the Pr-modified MnO\({}_{\rm x}\) catalyst displays markedly improved SO\({}_{2}\) resistance (Figure 8). Characterization indicated that the Pr-modified MnO\({}_{\rm x}\) catalyst improves the specific surface area, dispersion, reducibility, and relative percentage of the catalyst's surface Mn\({}^{4+}\) and chemisorbed oxygen (O\({}_{\rm a}\)). The results of NH\({}_{3}\)-TPD and in situ drift experiments demonstrated that Pr modification increases NH\({}_{3}\) adsorption on the catalyst surface, resulting in more Lewis acid sites on the MnPrOx-0.1 catalyst's surface. These factors contribute to the excellent catalytic performance of the Pr-modified MnO\({}_{\rm x}\) catalyst. Using a sacrificial template, Cheng et al. [61] developed a MnO\({}_{\rm x}\)-PrOx catalyst with an urchin-like hollow core-shell structure. The catalyst with a Pr/Mn molar ratio of 0.3 exhibits the highest NO conversion rate at 120 \({}^{\circ}\)C, nearly 99%. In the temperature range of 100 \({}^{\circ}\)C to 240 \({}^{\circ}\)C, the NO conversion rate exceeds 90%. The MnO\({}_{\rm x}\)-PrOx catalyst shows strong SO\({}_{2}\) and H\({}_{2}\)O resistance in 100 ppm SO\({}_{2}\) and 10% H\({}_{2}\)O with a space velocity of 40,000 h\({}^{-1}\) and a test duration of 3 h at 160 \({}^{\circ}\)C. The catalyst's excellent low-temperature catalytic activity is attributed to the high concentration of Mn\({}^{4+}\) and surface-adsorbed oxygen, conferring suitable Lewis acidity and good reducibility to the surface properties. Figure 8: The promoting effect and reaction mechanism of Pr modification on SO\({}_{2}\) resistance over the MnO\({}_{\rm x}\) catalyst. (Reproduced with permission from Ref. [34]. Copyright 2022, Springer Nature, Berlin/Heidelberg, Germany). Modification can improve the specific surface area and surface acid strength of the MnO\({}_{\text{x}}\) catalyst. Li et al. [35] prepared a series of modified Mn oxide catalysts with varying proportions using the homogeneous precipitation method.