Critical Role of Mullite-type Oxides’ Surface Chemistry on Catalytic NO Oxidation Performance

Abstract

By combining low energy ion scattering spectroscopy and density functional theory calculation, we study the surface composition and surface formation energy of AMn2O5 (A = Sm, Bi) mullite-type oxides synthesized by different methods and their effects on NO catalytic performance. It is well-known that hydrothermal (HT) synthesis at low temperatures produces materials with higher specific surface areas (SSAs) compared with those synthesized by coprecipitation (CP) and high-temperature calcination; however, it is less clear how synthesis methods affect surface chemistry. We find that the NO oxidation performance of SmMn2O5–HT does not match the SSA increase when compared to the lower SSA SmMn2O5–CP. Combined experimental and theoretical investigation reveals that SmMn2O5–HT includes a higher fraction of inactive Sm-terminated surfaces, which explains its lower than expected activity. However, the surface chemistry change depends strongly on the A-site element. The exposed surfaces of BiMn2O5–CP are predomina...