## 5 Nano-Mn-Based Catalyst
### Single MnO\({}_{\text{x}}\) Nanocatalysts  
Many reports have highlighted that the structure of a single MnO\({}_{\text{x}}\) nanocatalyst greatly affects its denitrification performance. To explore the relationship between catalytic efficiency and structure, Li et al. [27] successfully synthesized manganese dioxide nanomaterials in various forms (nanospheres, nanosheets, nanorods) and performed characterization using SEM and TEM. Additionally, the SCR of NOx under ammonia conditions was used as an indicative reaction. The SCR activity of manganese dioxide nanomaterials with different shapes reveals a promising trend: manganese dioxide nanospheres > nanosheets  
Figure 16: The mechanism of the Pr-modified Fe-Mn-TiO\({}_{2}\) catalyst enhancing SO\({}_{2}\) resistance. (Reproduced with permission from Ref. [91]. Copyright 2020, Springer Nature).  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Catalyst** & **Preparation Method** & **Reaction Condition** & **Denitrification Activity** & **Refs.** \\ \hline Mn-Ce & hydrothermal process & (NO) = (NH\({}_{3}\)) = 500 ppm, 6\% O\({}_{2}\), & (100–325 \({}^{\circ}\)C) \textgreater{}60\% & [113] \\  & & 0.08\% (NO); 0.08\% (NH\({}_{3}\)), 5\% O\({}_{2}\), & (80–240 \({}^{\circ}\)C) \textgreater{}80\% & [61] \\ Mn-Zn-cordierite & co-precipitation & (NO) = (NH\({}_{3}\)) = 500 ppm, 3\% O\({}_{2}\), & (150–225 \({}^{\circ}\)C) \textgreater{}80\% & [114] \\ Mn-Ce-Ti & kinetics-controlled coating & (NO) = (NH\({}_{3}\)) = 500 ppm, 5\% O\({}_{2}\), & (40–200 \({}^{\circ}\)C) \textgreater{}95\% & [115] \\ Mn-Fe-Ti & co-precipitation & (NO) = (NH\({}_{3}\)) = 500 ppm, 5\% O\({}_{2}\), & (145–260 \({}^{\circ}\)C) \textgreater{}80\% & [116] \\ Mn-Cu-AC & co-precipitation & 0.12\% (NO); 0.17\% (NH\({}_{3}\)), 6\% O\({}_{2}\), & (200–250 \({}^{\circ}\)C) \textgreater{}90–95\% & [117] \\ Mn-Ce-Ti-CNTs & sol–gel & (NO) = (NH\({}_{3}\)) = 500 ppm, 5\% O\({}_{2}\), & (220–240 \({}^{\circ}\)C) \textgreater{}80\% & [118] \\ Mn-Ti-Ce-Zr & hydrolysis impregnation & (NO) = (NH\({}_{3}\)) = 500 ppm, 5\% O\({}_{2}\), & (150–250 \({}^{\circ}\)C) \textgreater{}80\% & [119] \\  & & GHSV = 60,000 h\({}^{-1}\) & & \\ \hline \hline \end{tabular}
\end{table}
Table 5: Representative nano-Mn-based catalysts and their denitration activity in the NH\({}_{3}\)-SCR reaction.  
\(>\) nanorods. Within the temperature range of 200 to 350 \({}^{\circ}\)C, MnO\({}_{2}\) nanospheres achieve a NO conversion rate of 100%. Gao et al. [120] synthesized a-MnO\({}_{2}\) nanorods, b-MnO\({}_{2}\) nanorods, and sea urchin-like c-MnO\({}_{2}\) catalysts featuring distinct tunnel structures through hydrothermal synthesis and evaluated their catalytic oxidation of NO. The experimental results indicated that the C-MnO\({}_{2}\) catalyst outperforms the other two, achieving a NO conversion rate of over 80% at 250 \({}^{\circ}\)C. The catalytic oxidation activity follows the order c \(>\) b \(>\) a.  
Due to the single composition of the MnO\({}_{x}\) catalyst alone, its denitrification performance remains inadequate even after refinement to the nanometer scale, which is far from meeting actual industrial demands. Therefore, to enhance the catalyst's denitrification performance, stability, and resistance to H\({}_{2}\)O and SO\({}_{2}\), more composite MnO\({}_{x}\) nanocatalysts have been developed.