Mixed-valence manganese oxide catalysed oxidation of benzyl alcohol and cyclohexanol in the liquid phase

Two types of mixed-valence manganese oxides were synthesised by a mechanochemical process in the solid phase by chemical reaction of manganese(II) chloride and potassium permanganate at room temperature. The prepared catalysts were characterised by surface area and pore size, particle size, XRD analyses, SEM analyses and oxygen content measurements. These oxides were used as catalysts for oxidation of benzyl alcohol and cyclohexanol in the presence of solvent and also in solvent-free conditions using molecular oxygen as oxidant. The oxidation reactions were heterogeneous in nature where the catalysts were separated from the reaction mixture by simple filtration. Reaction took place in two steps according to the Langmuir-Hinshelwood mechanism. Benzyl alcohol/cyclohexanol and oxygen adsorb at the surface of the catalyst in the first step followed by reaction between adsorbed benzyl alcohol/cyclohexanol in second step. 69.8 kJ mol^-1 and 140.8 kJ mol^-1 were calculated as the activation energy for benzyl alcohol and cyclohexanol in n-octane as the solvent respectively, with values of 65.1 and 76 kJ mol^-1 for benzyl alcohol and cyclohexanol in solvent-free conditions respectively.