Aerobic Oxidation of Cyclohexane Effectively Catalyzed by Simply Synthesized Silica-Supported Cobalt Ferrite Magnetic Nanocrystal

Silica-supported magnetic cobalt ferrite complex oxides, CoFe 2 O 4 /SiO 2, with different loading of 5, 10, 20, and 50% were simply prepared by a sol–gel autocombustion method using colloidal aqueous silica solution as a cheap silica source. The as-prepared samples were well characterized by X-ray diffractometry (XRD), Fourier transform infrared spectrophotometry (FT-IR), transmission electron microscopy (TEM), and N 2 physisorption. Metals contents of the samples were also determined by atomic absorption spectrophotometry. Their catalytic performances were evaluated on cyclohexane oxidation using oxygen as oxidant in the absence of solvents and reductants. The supported catalysts have shown high catalytic activities for cyclohexane oxidation. Especially, when 5% loading of CoFe 2 O 4 /SiO 2 was employed, 4181 turnover number and 95.4% selectivity for cyclohexanone and cyclohexanol were obtained under 1.6 MPa of initial oxygen pressure at 418 K after 6.0 h of reaction. The sample of 50% of CoFe 2 O 4 /SiO 2 has strong magnetism and can be magnetically separated easily. This sample was employed as catalyst to optimize the reaction conditions. The catalyst showed prominent reusability, and no obvious loss in activity was observed when reused in six consecutive runs.