Oxygen Vacancy-Driven Improvement of NH3-SCR Performance over α-MnO2: Mechanistic Insights

Nitrogen oxides (NOx), harmful pollutants primarily from fossil fuel combustion, pose significant environmental and health risks. Among mitigation technologies, NH3-SCR is widely adopted due to its high efficiency and industrial viability. MnO2-based catalysts, particularly α-MnO2, have gained attention for low-temperature NH3-SCR owing to their redox properties, low-temperature activity, and environmental compatibility. In this study, α-MnO2 catalysts with tunable oxygen vacancy concentrations were synthesized by varying calcination atmospheres. Compared to α-MnO2-Air, the oxygen vacancy-rich α-MnO2-N2 exhibited stronger acidity, enhanced redox properties, and superior NH3/NO adsorption and activation, achieving 98% NO conversion at 125–250 °C. Oxygen vacancies promoted NH3 adsorption on Lewis/Brønsted acid sites, facilitating -NH2 intermediate formation, while enhancing NO oxidation to reactive nitrates. In situ DRIFTS revealed a dual E-R and L-H reaction pathway, with oxygen vacancies crucial for NO activation, intermediate formation, and N2 generation. These findings underscore the importance of oxygen vacancy engineering in optimizing Mn-based SCR catalysts.