Solvent-free Liquid Phase Catalytic Oxidation Of Cyclohexane To Cyclohexanone Over Ce-MIL-101(Cr、Fe)

Metal-organic frameworks (MOFs) are currently of great interest in the recent years as promising new materials due to their advantages of properties and structures. MOFs are attractive heterogeneous catalysts since they possess separated catalytic active sites in their frameworks which are characteristics of the homogenous catalysts. These sites are in the constitutional metal codes which have free or exchangeable coordination positions. Because of possessing the high porosity, tunable pore size and adjustable internal surface properties, MOFs can exhibit high catalytic activity, especially when active metal ions are doped into their pores or structures.Under mild conditions selective oxidation of cyclohexane to a mixture of cyclohexanol and cyclohexanone are important chemical raw materials, at the same time they are industrial intermediates of great importance. However, due to the larger bonding energy and the weaker polarity of the carbon-hydrogen bond. So far the commercial oxidative processes of cyclohexane to cyclohexanone and cyclohexanol generally has showed many disadvantages, such as low conversion, poor selectivity, environmental pollution and so on. At the same time with the increase of social demand for cyclohexane oxidation products, scientists have been attempting to discover better heterogeneous catalytic ways of cyclohexane oxidation in the absence of solvents.The research here is intended to synthesis of a catalyst which could perform high activity under mild condition. Recently, cerium doped catalysts were found to be good at oxidizing cyclohexane to KA oil (mixture of cyclohexanone and cyclohexanol) efficiently at ambient temperature. And MIL-101 catalysts have shown excellent catalysis in the oxidation of cyclohexane. So we prepare MIL-101 catalysts modified by cerium through direct hydrothermal (DHT) method and their catalytic activities of cyclohexane are investigated.(1) All the samples were systematically characterized by a combination of techniques including XRD, XRF, FT-IR, N2 adsorption-desorption and SEM, which showed that the cerium atoms could make an influence on the framework of MIL-101. The surface area and pore volume of Ce-MIL-101 decreased after modification.(2)The catalytic activity of the Ce-MIL-101 was elaborately investigated. The optimum reaction conditions are 1 mL cyclohexane with temperature at 70℃ and reaction time for 12 hours in absence of any solvent. When 4 mL tert-butyl hydroperoxide (TBHP) was used as oxidizing agent and 15mg Ce/Cr-MIL-101(8 wt%) was used as catalyst, the conversion of cyclohexane and selectivity of KA oil were 47.7% and 55.7%, respectively. When 3 mL tert-butyl hydroperoxide (TBHP) was used as oxidizing agent and 20 mg Ce/Fe-MIL-101(5 wt%) was used as catalyst, the conversion of cyclohexane and selectivity of KA oil were 49.4% and 100%, respectively.