| Summary: | Manganese oxides (MnO<i><sub>x</sub></i>) have attracted particular attention in the selective catalytic reduction of NO<i><sub>x</sub></i> with NH<sub>3</sub> (NH<sub>3</sub>-SCR) because of their excellent low-temperature activity. Herein, we prepared a highly efficient MnO<sub>2</sub> (MnO<sub>2</sub>-M) catalyst through a facile ball milling-assisted redox strategy. MnO<sub>2</sub>-M shows a 90% NO<i><sub>x</sub></i> conversion in a wide operating temperature window of 75–200 °C under a gas hourly space velocity of 40,000 h<sup>−1</sup>, which is much more active than the MnO<sub>2</sub> catalyst prepared by the redox method without the ball-milling process. Moreover, MnO<sub>2</sub>-M exhibits better H<sub>2</sub>O and SO<sub>2</sub> resistance. The enhanced catalytic properties of MnO<sub>2</sub>-M originated from the high surface area, abundant oxygen vacancies, more acid sites, and higher Mn<sup>4+</sup> content induced by the ball-milling process. In situ DRIFTS studies probed the reaction intermediates, and the SCR reaction was deduced to proceed via the typical Eley–Rideal mechanism. This work provides a facile method to enhance the catalytic performance of Mn-based catalysts for low-temperature denitrification and deep insights into the NH<sub>3</sub>-SCR reaction process.
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