Microwave frequency effects on synthesis of cryptomelane-type manganese oxide and catalytic activity of cryptomelane precursor

Cryptomelane-type manganese oxides (OMS-2) were synthesized in the presence of microwave heating at different microwave frequencies and also using variable-frequency heating. The materials were prepared using a two-step hydrothermal procedure. Catalytic activity of the materials was tested for the oxidation of 2-thiophenemethanol. OMS-2 prepared at a high-frequency limit of 5.5 GHz showed the highest conversion (50%) to the 2-thiophenecarboxaldehyde among all of the tested OMS-2 samples. The OMS-2 precursor showed remarkable conversion (89%) in the oxidation reaction. In addition, the OMS-2 materials and the precursor showed differences in oxygen evolution based on the thermal decomposition experiments, as well as differences in porosity.