## 4 Ternary and Multivariate Mn-Based Multi-Metal Oxide Catalysts
### MnO\({}_{x}\)-CeO\({}_{2}\)-X Catalysts
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Catalyst** & **Preparation Method** & **Reaction Condition** & **Denitrification Activity** & **Refs.** \\ \hline Mn-Nd-Ti & co-precipitation & (NO) = (NH\({}_{3}\)) = 600 ppm, 3\% O\({}_{2}\), & (130–320 \({}^{\circ}\)C) \(\sim\)100\% & [75] \\ Mn-Sm-Ti & co-precipitation & (NO) = (NH\({}_{3}\)) = 500 ppm, 5\% O\({}_{2}\), & (150–300 \({}^{\circ}\)C) \(\sim\)100\% & [76] \\ Mn-Fe-Ti & inverse co-precipitation & (NO) = (NH\({}_{3}\)) = 500 ppm, 5\% O\({}_{2}\), & (150–350 \({}^{\circ}\)C) \(>\)90\% & [77] \\ Mn-Cu-Ti & co-precipitation & (NO) = (NH\({}_{3}\)) = 500 ppm, 5\% O\({}_{2}\) & 200 \({}^{\circ}\)C \(>\) 90\% & [78] \\ Mn-V-Ti & excessive impregnation & (NO) = (NH\({}_{3}\)) = 500 ppm, 5\% O\({}_{2}\), & (275–550 \({}^{\circ}\)C) \(>\)80\% & [79] \\ Mn-Sn-Ti & polymer-directed self-assembly & (NO) = (NH\({}_{3}\)) = 500 ppm, 5\% O\({}_{2}\) & (220–400 \({}^{\circ}\)C) \(>\)80\% & [80] \\ Mn-Ni-Ti & wet impregnation & (NO) = (NH\({}_{3}\)) = 400 ppm, 2\% O\({}_{2}\), & (200–250 \({}^{\circ}\)C) \(\sim\)100\% & [81] \\ Mn-Eu-Ti & sol–gel & (NO) = (NH\({}_{3}\)) = 600 ppm, 5\% O\({}_{2}\), & (200–400 \({}^{\circ}\)C) \(>\)90\% & [82] \\ Mn-Zr-Ti & wet impregnation & (NO) = (NH\({}_{3}\)) = 500 ppm, 4\% O\({}_{2}\), & (200–360 \({}^{\circ}\)C) \(\sim\)100\% & [83] \\ Mn-Ce-Fe-Co-Ti & wet impregnation & (NO) = (NH\({}_{3}\)) = 500 ppm, 6\% O\({}_{2}\), & (125–250 \({}^{\circ}\)C) \(>\)80\% & [84] \\ Mn-Ce-Ho-Ti & wet impregnation & 0.08\% (NO); 0.08\% (NH\({}_{3}\)), 5\% O\({}_{2}\), & (140–220 \({}^{\circ}\)C) \(>\)90\% & [85] \\ Mn-Ce-Sm-Ti & co-precipitation & (NO) = (NH\({}_{3}\)) = 500 ppm, 5\% O\({}_{2}\), & (225–275 \({}^{\circ}\)C) \(>\)80\% & [86] \\ Mn-Ce-Ru-Ti & wet co-impregnation & (NO) = (NH\({}_{3}\)) = 550 ppm, 5\% O\({}_{2}\), & (18–250 \({}^{\circ}\)C) \(>\)90\% & [87] \\ Mn-Ce-Fe-Ti & sol–gel & 0.06\% (NO); 0.06\% (NH\({}_{3}\)), 3\% O\({}_{2}\), & (140–260 \({}^{\circ}\)C) \(>\)80\% & [88] \\ Mn-Ce-V-W-Ti & wet impregnation & (NO) = (NH\({}_{3}\)) = 1500 ppm, 3\% O\({}_{2}\), & (150–400 \({}^{\circ}\)C) \(>\)90\% & [89] \\ Mn-Ce-Co-Ti & impregnation & (NO) = (NH\({}_{3}\)) = 1000 ppm, 5\% O\({}_{2}\), & (130–320 \({}^{\circ}\)C) \(>\)90\% & [90] \\ Mn-Fe-Pr-Ti & wet impregnation & 0.1\% (NO); 0.1\% (NH\({}_{3}\)), 7\% O\({}_{2}\), & (140–220 \({}^{\circ}\)C) \(>\)95\% & [91] \\ Mn-Ce-Ti-Sn & co-precipitation & (NO) = (NH\({}_{3}\)) = 500 ppm, 5\% O\({}_{2}\), & (225–275 \({}^{\circ}\)C) \(>\)80\% & [92] \\ Mn-Ce-Nb-Fe & co-precipitation & (NO) = (NH\({}_{3}\)) = 500 ppm, 5\% O\({}_{2}\), & (125–275 \({}^{\circ}\)C) \(>\)80\% & [93] \\ \hline \hline \end{tabular}
\end{table} 
Table 4: _Cont._Al doping can enhance MnO\({}_{\text{x}}\)-CeO\({}_{2}\) catalysts by creating a wide range of pore structures, thus offering a larger reaction surface area. Wang et al. (2019) prepared MnO\({}_{\text{x}}\)-CeO\({}_{2}\)-Al\({}_{2}\)O\({}_{3}\) catalyst using the self-propagating high-temperature synthesis (SHS) method. This catalyst achieves a 100% NO conversion rate at 200 \({}^{\circ}\)C and a space-time velocity of 15,384 h\({}^{-1}\). The effective SCR temperature window for NO conversion exceeding 90% ranges from 150 to 300 \({}^{\circ}\)C. At 200 \({}^{\circ}\)C, the MnO\({}_{\text{x}}\)-CeO\({}_{2}\)-Al\({}_{2}\)O\({}_{3}\) catalyst exhibits strong resistance to SO\({}_{2}\) (100 ppm) and H\({}_{2}\)O (5%). Characterization results indicated that the pronounced synergy between Mn and Ce, along with the comprehensive pore structure of the MnO\({}_{\text{x}}\)-CeO\({}_{2}\)-Al\({}_{2}\)O\({}_{3}\) catalyst, significantly improves the activity of the low-temperature SCR reaction. V doping enhances the surface acidity of the MnO\({}_{\text{x}}\)-CeO\({}_{2}\) catalyst. Yang et al. (2019) developed a series of spherical VO\({}_{\text{x}}\)-MnO\({}_{\text{x}}\)-CeO\({}_{2}\) catalysts using the initial wet impregnation method.