Study On Catalytic Oxidation Of Cyclohexane Over Cobalt-based Materials Derived From ZIF-67

The selective oxidation of cyclohexane to produce cyclohexanone and cyclohexanol(KA oil)is an important part of nylon synthesis process.At present,in order to obtain a high KA oil selectivity,a low conversion of cyclohexane should be maintained,which leads to low production efficiency and high energy consumption.Therefore,the development of highly effective catalysts is the key to solve the above problems.In this paper,Co-based catalysts were prepared for cyclohexane oxidation by using ZIF-67 as a precursor.Physicochemical nature of the catalyst and catalytic oxidation performance were scientificly studied,and the relationship between the structure of catalysts and the reaction performance was revealed,providing theoretical support for the development and design of efficient catalysts.1.Characterization and performance study of(Ce,Ni)-modified Co3O4 catalyst derived from ZIF-67The composite metal oxide catalysts xCeO2-Co3O4,yNiO-Co3O4,and xCeO2-yNiO-Co3O4 were prepared by loading Ce and Ni with ZIF-67 as precursors before being calcinated in air at high temperature.Studies have shown that the Co3O4 particles obtained by calcination at 400? are highly dispersed and have rich pore structure,exhibiting high catalytic activity for cyclohexane oxidation(cyclohexane conversion rate of 9.7%)and KA oil selectivity(90.3%).Further researches found that the doping of Ce/Ni is beneficial to the dispersion of Co3O4 and the formation of oxygen vacancies.This is because the second metal interacts with Co3O4,which limits the growth of Co3O4 grains and oxygen vacancies are induced at the two-phase interface.When Ce/Ni/Co=0.1/0.2/1.0,the catalytic performance is first-rank,the cyclohexane conversion rate reaches 12.8%,and the selectivity of KA oil reaches 95.5%,this is attributed to the fact that highly dispersed Co3O4 provids a large number of active sites and oxygen vacancies,which are conducive to the activation of oxygen molecules.2.Characterization and performance study of cobalt/carbon nanotube catalysts based on ZIF-67The cobalt catalyst(wCo-CoxOy/CN)with a controlled cobalt valence state was prepared by impregnating cobalt using ZIF-67 as the precursor and in situ selective reduction at high temperature in nitrogen.The study shows that as the cobalt loading increases,the relative content of Co0 decreases from 0.3(51Co-CoxOy/CN)to 0.23(73Co-CoxOy/CN),while the relative content of Co2+ shows a volcanic trend.The relative content of Co2+ and oxygen vacancy value is maximized in 68Co-CoxOy/CN catalyst.Moreover,the performance of the catalyst first increased,and then declined with the increase of cobalt loading.When 68Co-CoxOy/CN material was used as catalyst,the catalytic performance was optimal,with the conversion rate of cyclohexane reaching 16.7%and the selectivity of KA oil reaching 97.3%.This is because the interaction between the strengthened metal cobalt and cobalt oxide leads to the formation of a large number of oxygen vacancies,and the catalyst has larger specific surface area which can provid more active sites.3.Study the catalytic performance of water produced by the reaction on cyclohexaneWater has a significant effect on the progress of cyclohexane oxidation and catalytic performance.It is found that adding water absorbent(MgO?CaO and Al2O3)to the reaction system can effectively absorb the generated water,thus avoiding the quenching of free radicals and increasing the oxidation rate of cyclohexane.At the same time,the absorption rate of the adsorbent dramatically affects the catalytic performance,and the appropriate absorption rate is conducive to the oxidation reaction.MgO has good hydrophility and suitable specific surface area,so that it has a moderate absorption rate.Therefore,the catalytic oxidation performance of cyclohexane is significantly ameliorated,the conversion rate of cyclohexane is 20.0%and the selectivity of KA oil is 98.0%.In this paper,the cobalt-based oxide catalyst prepared with ZIF-67 as precursor showed good activity for the selective oxidation of cyclohexane and high selectivity for KA oil.The effects of the physicochemical natures of the catalyst on its catalytic performance were systematically researched.At the same time,the high active sites of cyclohexane oxidation and the mechanism of water in the oxidation reaction were elucidated to provide theoretical guidance and technical support for the preparation of highly efficient catalysts.