Enhanced catalytic oxidation of toluene over manganese-based multi-metal oxides synthesized by ozone driving redox reaction

A series of heteroatom-doped MnO2 have been successfully synthesized by the ozone driving redox reaction, wherein the Fe, Co, Ni and Cu were directly introduced into MnO2. It was inferred that the doped heteroatoms existed in the form of Fe2+, Fe3+, Fe4+, Co3+, Ni3+, Cu2+ and Cu3+ in MnO2 by the characterization of XRD, XPS, Raman and HRTEM. Their catalytic activities of toluene oxidation were positively correlated with the molar ratios of (Mn2++Mn3+)/Mn4+, the proportion of adsorbed oxygen species and the low-temperature reducibility. The larger radius of high-valence Fe ions led to obvious structural distortion of MnO2, which brought about more active oxygen species on the surface of the most active Fe-MnO2. According to BET and SEM characterization, the high specific surface area and nanostructure should contribute to the high activity of Fe-MnO2. In addition, the in-situ DRIFTS confirmed that the first functional group adsorbed on the surface of Fe-MnO2 was the methyl group, and thus toluene was oxidized to some carbonyl-containing species. TD/GC-MS detection showed that the organic compounds existed in the exhaust gas. Ultimately, the catalytic mechanism and the degradation of toluene oxidation were also discussed.