Selective Catalytic Oxidation Of Cyclohexane Over Modified Metal-organic Frameworks

The mixture of cyclohexanol and cyclohexanone?KA oil?is an important chemical intermediate and petrochemical raw material.At present,cyclohexane oxidation is an important chemical process for preparing KA oil.In the industrial cyclohexane oxidation process,reasonable selectivity to the desired intermediate KA oil is achieved at a lower conversion.Developping catalyst of high efficiency,good selectivity and environmental-friendly feature is an urgent need for the cyclohexane oxidation.Metal-Organic Frameworks?MOFs?are intensively studied as heterogeneous catalyst support for their high surface area,tunable crystalline structure.In this thesis,a series of modified vanadium-based and iron-based MOFs were obtained by introducing the 2^nd metal species to the MOF support.The effects of hydrophobic modification and the reaction parameters on the catalytic performance of cyclohexane were investigated.The main research contents are as follows:?1?Zr-UiO-66 was synthesized and modified with two approaches.Various ratio of fluorine group was introduced to the organic ligand to tune the surface hydrophobicity of Zr-UiO-66.Amino group was prefuncationalized on the MOF ligand,allowing further modification to constructed Schiff based chelating sites,thus,VO?acac?₂ was anchored on the Schiff-based sites.A series of vanadium complex modified Zr-UiO-66 were obtained,namely,Zr-UiO-66-1/4NH₂-sal/VO?acac?,Zr-UiO-66-1/4NH₂-1/4F-sal/VO?acac?,Zr-UiO-66-1/4NH₂-3/4F-sal/VO?acac?.Ce-UiO-66 material was synthesized with the same topology of Zr-UiO-66,only differs in the metal sites.Fe₃O₄@Ce-UiO-66 was obtained by one-pot synthesis approach with Fe₃O₄ as the template.The above series of modified MOFs were characterized means of X-ray powder diffraction?XRD?,fourier transform infrared?FT-IR?,scanning electron microscopy?SEM?,transmission electron microscopy?TEM?,N₂ physical adsorption and inductively coupled plasma atomic emission spectroscopy?ICP-AES?.?2?The catalytic performance of modified vanadium-based Zr-UiO-66 and iron-based Ce-UiO-66 in the liquid phase oxidation of cyclohexane was evaluated.The results showed that hydrophobic modfication on the vanadium-based catalyst has positive effect on the catalytic performance both in conversion and selectivity.At 70 ^oC,with tert-butyl hydroperoxide?TBHP?as the oxidant and acetonitrile as the solvent,Zr-UiO-66-1/4NH₂-1/4F-sal/VO?acac?has the best catalytic activity,with cyclohexane conversion of 6%and KA oil selectivity of 70.5%in 12 h.With Fe₃O₄ as the catalytically active speicies,Fe₃O₄@Ce-UiO-66 showed an enhanced catalytic activity of 6.9%conversion and 92.1%selectivity of KA oil in 5 h at 90 ^oC,0.5 MPa O₂,in the presence of small amount of TBHP.