Clarify the effect of different metals doping on α-MnO2 for toluene adsorption and deep oxidation

α-MnO2 doped with four metals (Cu, Ce, Co, Fe) were prepared via a redox co-precipitation method. MnCu exhibited the highest activity and the temperature required for achieving 90% toluene conversion was 224℃ at a weight hourly space velocity of 30000 mL·g−1·h−1. Moreover, MnCu possessed outstanding thermal stability and resistance to H2O. The optimal crystal structure, appropriate Mn3+/Mn4+ proportion, and superior redox properties of MnCu contributed to the generation of oxygen vacancies and the highest lattice oxygen (Olat) mobility. Both surface and bulk lattice oxygen consumed in MnCu can be supplemented promptly by gaseous oxygen. Therefore, a balance between toluene adsorption and deep oxidation was built in MnCu to ensure the continuous oxidation of toluene. Although the abundant surface defects and a relatively active surface lattice oxygen accelerated the adsorption and activation of toluene over MnFe, it exhibited the poorest activity. This was because the deep oxidation of toluene was inhibited owing to poor lattice oxygen migration. The adsorbed toluene and part intermediates might cover the catalyst surface preventing the continuous oxidation of toluene. This further illustrated that the deep oxidation of toluene was much more important than the adsorption for the design of MnO2-based mixed oxide catalysts.