Thermal stability of MnOx–CeO2 mixed oxide for soot combustion: influence of Al2O3, TiO2, and ZrO2 carriers

Abstract

MnO_x–CeO₂ (Mn/Ce = 0.15/0.85) mixed oxide materials supported on ZrO₂, Al₂O₃, and TiO₂ were prepared by citrate sol–gel method to prevent the CeO₂-based oxide catalyst from sintering during soot combustion reaction. The materials were characterized using XRD, BET method, HRTEM, H₂-TPR, and XPS. Results indicate that the MnO_x–CeO₂/TiO₂ catalyst is rapidly sintered at 800 °C because of the TiO₂ phase change from anatase to rutile. By contrast, MnO_x–CeO₂ catalysts supported on Al₂O₃ and ZrO₂ show high thermal stability. After aging at 800 °C for 10 h, the MnO_x–CeO₂ crystalline structure remained highly dispersed on the carrier. Particularly with the ZrO₂ carrier, the amount of surface oxygen species and redox properties of MnO_x–CeO₂ can be well-maintained for the synergistic effect of CeO₂ and ZrO₂ in high temperature environments. Good agreement is found between the low-temperature redox property (200 °C to 400 °C) and the soot combustion activity of the catalysts.