## 8 Conclusions and Foresight  
Mn-based catalysts have demonstrated an excellent catalytic performance in low-temperature NH\({}_{3}\)-SCR reactions and have been the focus of extensive research as catalysts for the low-temperature NH\({}_{3}\)-SCR of NOx over the past many years. This paper provides a detailed introduction to four forms of manganese oxide-based catalysts: single manganese oxide-based catalysts, binary Mn-based metal oxide catalysts, ternary and multivariate Mn-based metal oxide catalysts, and nano-Mn-based catalysts. Numerous studies have reported advancements in improving the NOx conversion, N\({}_{2}\) selectivity, and H\({}_{2}\)O and SO\({}_{2}\) resistance of Mn-based catalysts by optimizing the preparation methods, altering the oxidation state of the active components, modifying the crystal phase, adjusting morphology and dispersion, incorporating one or more metals, lowering the activation energy of the reaction, and changing the types of active intermediates. The mechanism of low-temperature NH\({}_{3}\)-SCR reactions has been elucidated through various characterization techniques. Despite the significant progress made in the research of Mn-based catalysts for low-temperature NH\({}_{3}\)-SCR, there are still many areas that require further examination. At present, the main problems to be solved and the future development prospects are as follows:  
1. A new Mn-based catalyst has been developed, boasting high denitration efficiency, exceptional resistance to H\({}_{2}\)O and SO\({}_{2}\), high N\({}_{2}\) selectivity, robust stability, a broad operating temperature window, and no evident defects. The ability of this catalyst to perform stably and efficiently in actual industrial settings is crucial to its commercial value. Any noticeable defect will considerably diminish its market appeal. Developing catalysts with such comprehensive performance remains a major challenge.
2. In Mn-based composite metal oxide catalysts, the synergistic effect between MnO\({}_{\text{x}}\) and one or more other metal oxides, and the specific impact of metal modifications on the electron transfer and crystal structure of Mn-based catalysts, are not well understood. Further research is needed.
3. The intricate mechanism by which H\({}_{2}\)O and SO\({}_{2}\) inhibit Mn-based catalysts remains a significant challenge for their practical use. Further investigation into the inhibitory effects of H\({}_{2}\)O and SO\({}_{2}\) on low-temperature denitrification activity is required, which will lay a theoretical basis for developing Mn-based catalysts with high water and sulfur resistance.
4. The specific chemical interactions occurring on the catalyst's surface during the SCR denitrification process warrant further investigation. Despite numerous reports on  
Figure 28: Low-temperature SCR reaction mechanism model on the Mn\({}_{\text{x}}\)Moy-(\(\gamma\)-Al\({}_{2}\)O\({}_{3}\)) catalyst. (Reproduced with permission from Ref. [123]. Copyright 2020, Elsevier).  
the E-R mechanism, the L-H mechanism, and the coexistence of both, the NH\({}_{3}\)-SCR mechanism at low temperatures remains unclear. As analytical methods advance, it is anticipated that the adsorption states and reaction processes of reactants on the catalyst surface will be further elucidated. With the aid of more advanced analytical techniques, it is expected that a clearer understanding of the denitration mechanism can be achieved.
* In real-world applications, the catalyst gradually deactivates over time due to poisoning, a consequence of the complex composition of blue gas. Developing Mn-based catalysts with robust resistance to various toxic components is of great importance.