Recent progress of low-temperature selective catalytic reduction of NO_x with NH₃ over manganese oxide-based catalysts

Selective catalytic reduction with NH₃ (NH₃-SCR) was the most efficient approach to mitigate the emission of nitrogen oxides (NO_x). Although the conventional manganese oxide-based catalyst had gradually become a kind of principal catalyst for the low-temperature NH₃-SCR reaction, there were still numerous defects. The growing demands for extensive operation temperature scope, strong SO₂ tolerance, and excellent catalytic activity had boosted the development of novel manganese oxide-based catalysts. In this review, three forms of manganese oxide-based catalysts were introduced in detail, including single manganese oxide catalysts, composite manganese oxide-based catalysts, and supported manganese oxide-based catalysts. The surface acidity and redox properties of manganese oxide-based catalysts could be strengthened by optimizing the preparation methods, exposing specific crystal planes, and constructing multiple active centers and sacrificial sites, which improved the SCR performance and anti-poisoning properties of catalysts. Secondly, we briefly summarized the NH₃-SCR reaction mechanism of manganese oxide-based catalysts, including the Eley-Rideal (E-R) mechanism and the Langmuir-Hinshelwood (L-H) mechanism. Finally, several overtures were proposed for the future research directions of manganese oxide-based catalysts for NH₃-SCR reaction, hoping to narrow the gap between the novel manganese oxide-based catalysts and the actual demands and realize commercialized application in the nearest future.