Preparation Of ZIFs Derived Cobalt-based Material And Study On Catalytic Oxidation Of Benzyl Alcohol To Benzaldehyde

As an important chemical raw material intermediate,benzaldehyde not only plays an important role in many chemical reactions,but also has a wide range of applications in medicine,food and other chemical fields closely related to people’s lives.In domestic chemical production,benzyl chloride hydrolysis method and toluene direct oxidation method are relatively mature,but they have shortcomings such as chlorine content and many by-products,which limit their application in food,medicine and other industries,and do not meet the development requirements of"green chemical industry".Using molecular oxygen(air)as oxidant and green environmental material as catalyst,the method of liquid phase oxidation of benzyl alcohol to benzaldehyde has the advantages of simple operation,no pollution and high yield,so it has the significance of further research.This paper is devoted to the development of a clean and environmentally friendly catalyst for the efficient production of benzaldehyde.In this paper,ZIF-67 crystal was first synthesized by room temperature stirring method,and then ZIF-67 was used as self-sacrificing template to prepare Co O_X and Co@CN67 under high temperature heat treatment in air and argon atmosphere,respectively,for the study of liquid phase oxidation of benzyl alcohol.The catalysts were characterized by XRD,XPS,SEM and BET.The cobalt oxide catalyst obtained by calcination of ZIF-67 in air showed low activity and selectivity to benzaldehyde,while Co@CN67 prepared by pyrolysis in argon atmosphere showed good reaction performance under mild conditions.The specific surface area and pore structure of Co@CN67-x catalysts prepared at different pyrolysis temperatures,as well as the size of Co grains,were significantly different,which affected the liquid phase oxidation of benzyl alcohol.The catalyst prepared at 800 ~oC showed excellent reactivity,selectivity and reusability.The Co@CN67-800 catalyst was further etched with 40%HF solution to obtain HF-Co@CN67-800 catalyst to investigate the reactive species of the catalyst.The results showed that the catalytic activity of etched catalyst HF-Co@CN67-800 for the conversion of benzyl alcohol was greatly reduced,and the conversion rate was 18%,in which the C or N species may have played a catalytic role.After further characterization analysis of the catalysts before and after the reaction,it was speculated that the synergistic effect between Co and N species was the main reason why Co@CN67-800 catalyst could realize the efficient conversion of benzyl alcohol.In the reaction process,pyridine nitrogen or Co-Nx and graphite nitrogen enhance the activation of the reactant molecules,and promote the efficient conversion of benzyl alcohol molecules.Finally,in this paper,different imidazole ligands were used to synthesize Co-ZIFs materials,which were pyrolyzed at 800~oC in argon atmosphere to obtain the corresponding derivative materials.A series of characterization analysis found that Co-ZIFs materials have differences in specific surface area and pore structure,surface morphology and thermal stability.The liquid phase oxidation results of benzyl alcohol show that the catalytic activity of ZIF-9 and ZIF-12 is better than that of ZIF-67,but the catalytic activity of the derived materials is not as good as Co@CN-800.