Efficient magnetic CoFe₂O₄ nanocrystal catalyst for aerobic oxidation of cyclohexane prepared by sol–gel auto-combustion method: effects of catalyst preparation parameters

Six magnetic spinel-type CoFe₂O₄ samples were prepared in the form of powder by a simple sol–gel auto-combustion method from precursor solutions with different metal concentrations (0.1–0.3 mol L⁻¹) and pH values (<1–10). The samples were characterized by X-ray diffractometry, Fourier transform infrared spectrophotometry, transmission electron microscopy and N₂-physisorption. Their catalytic performances for oxidation of cyclohexane were evaluated using oxygen as oxidant in the absence of solvents. The results show that pH values and metal concentrations of precursor solutions play important roles in the sizes, dispersions and morphologies of the CoFe₂O₄ nanoparticles, and thus in their catalytic performances. The sample resulted from precursor solution under the conditions of pH = 7 and metal concentration = 0.1 mol L⁻¹ with the largest surface area, exhibited the best catalytic performance with the highest cyclohexane conversion of 13.7 % and selectivity of 93.9 % for cyclohexanol and cyclohexanone. The CoFe₂O₄ nanocrystal is also found an efficient catalyst for oxidation of aliphatic and aromatic alkenes.