Mechanism of fast selective catalytic reduction of NO with NH3 over MnOX–CeO2 catalysts

Abstract

MnO_X–CeO₂ composites are promising candidates as low-temperature active catalysts for selective catalytic reduction (SCR) of NO with NH₃, which is a leading technology for controlling NO emissions from non-electric flue gases. In this study, we systematically investigate the fast-SCR mechanism over MnO_X–CeO₂ through theoretical and experimental approaches. Our results reveal that fast-SCR is coupled with standard SCR through three coupled redox cycles: Mn-redox, Ce-redox, and O₂–O_v (surface oxygen vacancy in CeO₂) cycles occurring at distinct active sites. Even under O₂-rich reaction conditions, the fast-SCR reaction route still needs to overcome a higher energy barrier of 1.56 eV in the rate-determining step compared to the energy barrier of 1.44 eV via the standard SCR route. Intriguingly, fast-SCR significantly enhances the SO₂ resistance and N₂ selectivity by reducing the residence time of NH₃ adsorbed on the Mn³⁺ ions in the center of MnO_X clusters; this suppresses the reaction of NH₃ with SO_X and minimizes its deep oxidation, thereby suppressing N₂O emission.