High-temperature calcination enhances the activity of MnOx catalysts for soot oxidation†

High-temperature calcination usually induces the sintering of catalysts, thus resulting in negative effects on their performance. However, in this study we surprisingly found that high-temperature calcination could enhance the activity of MnO_x catalysts for soot oxidation. Combined experimental and theoretical analysis revealed that high-temperature calcination of MnO_x (900 °C) could induce the generation of more oxygen defects, due to the transformation of α-MnO₂ to δ-MnO₂ and Mn₂O₃, with lower formation energy for oxygen defects. The generated oxygen defects would facilitate activation of surface chemisorbed oxygen, producing more active oxygen species, which can further oxidize NO to NO₂ to accelerate soot combustion. Therefore, MnO_x calcinated at 900 °C exhibited much higher activity for soot oxidation than that calcinated at 500 °C. This study provides significant insight into the effects of calcination temperature on MnO_x catalysts, thereby aiding in the design of high-efficiency catalysts for the control of soot emission.