Effect of microwave absorption properties and morphology of manganese dioxide on catalytic oxidation of toluene under microwave irradiation

A large number of studies had shown that the morphology of the sample had a significant effect on the microwave absorption properties and catalytic activity of the sample. Manganese dioxide with different morphologies was synthesized by hydrothermal method through different precursors. The effects of sample morphology and microwave absorption properties on the catalytic activity of the sample in conventional thermal and microwave fields were studied. The results indicated that compared with the conventional thermal field, the catalytic activity of the samples in microwave field were obviously improved, and the activation energy of the reaction were decreased. Compared with the conventional thermal field, the conversion of toluene in microwave thermal field of MnO₂(Ac), MnO₂(S) and MnO₂(N) increased by 59%, 42% and 12%, and the mineralization rate increased by 36%,11% and 2%, respectively, when the catalytic temperature was 150 °C. Compared with the traditional thermal field, the activation energy of the sample MnO₂(Ac) in the microwave field was reduced by 88.3 KJ. A series of characterization results showed that the sample MnO₂(Ac) had good catalytic activity in the microwave field was due to: MnO₂(Ac) had proper microwave absorption properties, large amount of surface functional groups, large specific surface area and rich pore structure. The analysis results of electromagnetic parameters showed that: the reason that the sample MnO₂(Ac) had good microwave absorption performance was that the MnO₂(Ac) had proper impedance matching, high attenuation constant and Debye dipole relaxation effect.