Superior Low-temperature NO Catalytic Performance of PrMn2O5 over SmMn2O5 Mullite-type Catalysts

By studying their surface chemistry, metal–oxygen bond strength, and critical energy barrier heights, we elucidate the differences in the NO oxidation catalytic performance of PrMn2O5 and SmMn2O5 mullite-type oxides. The 50% conversion temperature is lower (230 °C vs. 275 °C) and the maximum conversion efficiency is higher (81% at 282 °C vs. 68% at 314 °C) for PrMn2O5 compared to SmMn2O5, despite having a ∼15% lower specific surface area. Furthermore, PrMn2O5 exhibits higher maximum efficiency compared to Pt/Al2O3. Combined experimental and theoretical findings indicate that the superior catalytic performance of PrMn2O5 at low temperatures arises from the presence of more labile and reactive surface lattice oxygen due to weaker Mn–O bond strength and lower thermal stability of surface NOx ad-species.