Rational design of SrMnO3/Mullite mixed-phase oxide as highly efficient catalysts for NO oxidation

Abstract

Catalytic oxidation of nitric oxide (NO) is a critical step for solving diesel engine exhaust issues. Owing to low cost and high thermal stability, mullite‐type oxides (e.g., SmMn₂O₅) are an efficient substitute for the commercial platinum-group-metal (PGM) catalysts. Here, a series of Sm_1−xSr_xMn₂O₅ catalysts were precisely synthesized by the sol-gel method. By introducing strontium (Sr) species, the NO oxidation activity improved significantly, and the optimum performance was achieved over Sm_0.6Sr_0.4Mn₂O₅ catalyst (92 % conversion at 270 °C). The XRD, TEM and XPS results show the formation of a mixed-phase oxide and the interfacial structure between the SmMn₂O₅ mullite and SrMnO₃ perovskite in the Sm_0.6Sr_0.4Mn₂O₅ sample. Compared with pure SmMn₂O₅ and SrMnO₃, the Sr substitution improves the specific surface area and amounts of surface adsorbed oxygen species and surface Mn active sites. The rich oxygen vacancies were also determined by the EPR, XPS and O₂-TPD technique, which also strengthen the NO adsorption. It reveals that all these factors benefit higher NO catalytic oxidation performance. This study provides an economic alternative to catalyze NO oxidation reactions in diesel oxidation catalysis.