Unveiling the remarkable deNOx performance of MnMoVOx catalysts via dual regulation of the redox and acid sites

Abstract

Developing NH3-SCR catalysts possessing excellent NO conversion, N2 selectivity, and alkali-tolerance at low-temperatures remains a great challenge. MnOx-based catalysts have attracted attention due to their exceptional low-temperature NH3-SCR activity. However, their strong oxidative capabilities often lead to excessive NH3 oxidation, causing a narrow operating temperature window and low N2 selectivity. In this study, we employed Mo and V to simultaneously fine-tune the acid and redox sites of MnOx, effectively suppressing the excessive NH3 oxidation at medium-high temperatures. The adjusted Mn0.90Mo0.09V0.01Ox catalyst demonstrated excellent low-temperature activity, a significantly broader active temperature window, and robust resistance to alkali metal poisoning. Multiple characterization results indicate that this dual acid-redox sites regulation strategy appropriately weakens the oxidative capacity while notably enhances surface acidity of the catalyst. Furthermore, the combination of in situ DRIFTS and DFT calculations reveal that following the adjustments of Mo and V on MnOx, new Brønsted acid sites are generated. Besides, the regulated catalyst evidently inhibits NO adsorption and nitrate species formation, thus promoting the reaction exclusively through the E-R mechanism, resulting in boosted N2 selectivity. This study also demonstrates that the optimum NH3-SCR performance of catalyst is achieved when oxidation ability and acid sites are harmoniously balanced, rather than following a "stronger is better" trend. In addition, through effective dual-active site regulation, the K-poisoning catalyst retains satisfactory catalytic activity. Thereby, the proposed dual-active sites regulation strategy in this study offers beneficial insights for the development of high-performance denitration catalysts.