Tuning the crystallinity of the MnO x catalysts to promote toluene catalytic oxidation

In this paper, the MnO_x catalysts with excellent toluene oxidation performance were prepared by a simple precipitation method. The physicochemical properties of the prepared MnO_x catalysts were investigated by XRD, BET, H₂-TPR, O₂-TPD and XPS. The obtained results revealed that the crystallinity of the prepared MnO_x catalysts could be effectively regulated by changing the (NH₄)₂CO₃/Mn(NO₃)₂ molar ratio, and thus affecting the oxygen vacancy concentration of the prepared MnO_x catalysts. The prepared MnO_x-4 catalyst with the (NH₄)₂CO₃/Mn(NO₃)₂ molar ratio of 4.0 had the poor crystallinity and small grain size, which effectively promoted the oxygen defects in the MnO_x catalyst to be formed. At the same time, the MnO_x-4 catalyst had a large specific surface area, the highest low temperature reducibility and the largest number of oxygen vacancies and surface adsorbed oxygen species, which allowed more surface oxygen species to participate in the redox reaction, and promoted the toluene deep oxidation. Therefore, when the (NH₄)₂CO₃/Mn(NO₃)₂ molar ratio was 4.0, the prepared MnO_x-4 catalyst exhibited an excellent toluene catalytic oxidation performance and robust catalytic stability. What's more, the toluene oxidation conversion on the MnO_x-4 catalyst reached 99% at 230°C, and the MnO_x-4 catalyst showed excellent resistance to water vapour.