Understanding the role of redox properties and NO adsorption over MnFeOx for NH3-SCR

Abstract

Widening the operational temperature window of the selective catalytic reduction of NO by NH₃ (NH₃-SCR) is a challenge to meet the increasingly stringent emission control regulations for NO_x. Hence, MnFeO_x with different molar ratios were prepared and investigated for NH₃-SCR. Mn–Fe-0.2 (Mn/Fe molar ratio of 0.2) eliminates more than 80% of NO_x in the temperature range of 50 to 360 °C with a N₂ selectivity of higher than 90%. In addition, it also presents excellent SO₂/H₂O tolerance. Doping Mn not only inhibits the phase transformation of iron oxide (Fe₂O₃) but also strengthens the interaction between MnO_x and Fe₂O₃ due to the electron transfer between them, which leads to the formation of Mn–O–Fe. Meanwhile, the amounts of acid, redox properties, and NO adsorption could also be tuned. The generation of different types of nitrite/nitrate is dependent on the redox properties and NO adsorption strength, whereas the activity of nitrite/nitrate functions in a different reaction temperature zone. Therefore, tuning for moderate redox activity and the NO adsorption strength will help to extend the operational temperature window.