Study On The Preparation Of Co-MOF And Their Catalytic Performance In The Oxidation Of Cyclohexane

That the selective oxidation of cyclohexane to prepare KA oil is one of the representative reactions of C-H bond oxidation in alkanes.The target products,KA oil（cyclohexanol and cyclohexanone）,are important intermediates for the production of raw materials for nylon 6,nylon 66 and other resin.Because cyclohexane molecules are more stable than cyclohexanol and cyclohexanone molecules,the cyclohexanol and cyclohexanone generated during the oxidation of cyclohexane are easily over-oxidized to organic acids as by-products,and then esterified to form ester by-products.Therefore,this reaction is difficult to satisfy high cyclohexane conversion and high KA oil selectivity at the same time.Generally,KA oil yield is increased by sacrificing cyclohexane conversion.Due to the high specific surface area of metal-organic framework materials,the adjustable pore structure,and easy functionalization,metal-organic framework materials have been widely studied in the field of catalysis.In this paper,ZIF-67 was used to coatto form a core-shell typewith the synergistic effect of different catalytic active sites.The bimetal synergistic catalysis inwas discussed through experimental characterization.Experiments show that high Mn³⁺/Mn²⁺has a higher activation effect on the C-H bond in cyclohexane,which is helpful for the conversion of cyclohexane to cyclohexyl hydrogen peroxide.At the same time,it proves that Co²⁺can promote the decomposition of CHHP.When the Co/Mn molar ratio is6,has the best catalytic performance.In addition,due to the presence of the Mn element in thestructure,the Co-N coordination in ZIF-67 has changed.In this paper,the second metal M（M=Mn,Ni,Cu,and Zn）was introduced into the ZIF-67framework to investigate the induction of defect structures in ZIF-67 by different M.The experimental characterization results showed that the introduction of Ni significantly promoted the increase of defect structures（metal defects and ligand defects）in the ZIF-67skeleton,which improved the redox reaction（ORR）activity of the ZIF skeleton structure.When the Co/Ni molar ratio is 4,Co-Ni-BMZIF shows the best catalytic performance.Inspired by the characteristic that cyclohexane possessing lower polarity than cyclohexanol and cyclohexanone,the coating of a hydrophobic Sishell on the surface of ZIF-67 on the one hand changed the hydrophilic-hydrophobic nature of the catalyst,the adsorption-desorption situation of cyclohexane,cyclohexanone and cyclohexanol molecules on the catalyst was altered and the catalytic activity for the oxidation reaction of cyclohexane was improved.On the other hand,the stability of the active components of the catalyst was improved.It was shown that the hydrophobic ZIF-67@Siprepared under the condition of TEOS volume fraction of 10%,using 3-chloropropyltriethoxysilane（3-CPTEOS）as a hydrophobic modifier in ethanol environment,behaved the best catalytic performance.It catalyzed the oxidation reaction of cyclohexane at a reaction temperature of 150℃and anpressure of 1MPa for 90 minutes,achieving a cyclohexane conversion rate of 11.35%and a selectivity of 80.46%to KA oil.And the catalyst was recycled four times without obvious loss of activity.