Enhancement of acidic sites in layered MnO2 for the highly efficient selective catalytic oxidation of gaseous ammonia

Abstract

Ammonia (NH3), as a typical harmful gaseous pollutant in atmosphere, poses a serious threat to human health and ecological environment. It is of great significance to develop the cost-effective catalysts with both excellent selective catalytic oxidation (SCO) activity and N2 selectivity. In this study, the acidic sites of layered MnO2 were regulated and its NH3-SCO performance was investigated. The enhancement of acidic sites in layered MnO2 significantly improved the SCO of NH3, and the resulting MnO2 could achieve complete conversion of NH3 at as lower as 100 °C, even better than the reported noble-metal catalysts. Furthermore, the improvement in NH3-SCO activity can be attributed to the abundant active oxygen species and enhancement of acidic sites (especially stronger Brønsted acidic sites). On the one hand, more active oxygen species can enhance the catalytic oxidation of NH3. On the other hand, Brønsted acidic sites acted not only as adsorption sites but also reaction sites, the increase in the content and strength of acidic sites facilitated the adsorption and activation of NH3. This research reveals the functional role of acidic sites in NH3-SCO, and provides a suggestive for the rational design of catalysts with excellent N2 selectivity and low-temperature NH3-SCO activity.