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

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 NOx. Hence, MnFeOx 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 NOx in the temperature range of 50 to 360 degrees C with a N-2 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 MnOx 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.