Study On The Preparation Of Catalysts And Their Catalytic Performance In The Oxidation Of Cyclohexane

Aerobic oxidation of liquid cyclohexane is an important chemical reaction process in industry and the products of reaction occupy an critical position in the field of chemical industry,which can be used as organic materials.The difficulty of the reaction lies in the activation of C-H bond which exists in saturated hydrocarbons.Due to the unique structure and characteristics,Metal-Organic Framework(MOF)materials is getting more and more applications in all areas recently,of which Zeolitic Imidazolate Frameworks(ZIF)materials catch especially notable attention.The higher performance of ZIF materials make up the defects of MOF materials and further promote application of MOF materials in chemical industry at the same time.So in this paper,we make great efforts to seek and synthesize excellent ZIF materials and attempt to combine it with constitutionally stable carbon nanotubes(CNTs)to prepare novel composite material.We applies this new composite material as catalyst for the liquid oxidation of cyclohexane,which may provide new insights into expanding the types of catalysts used in liquid aerobic oxidation of cyclohexane.The sepiolite from Xiangtan is used as catalyst in the reaction of cyclohexane oxidation at the beginning of this work.Experimental results show that the sepiolite has relatively good catalytic activity,whereas the concentration of by-products of this reaction,mainly acids and esters,increases which results in lower KA selectivity.Then we made an attempt to prepare ZIF materials cored on different metal Ni?Fe?Zn and Co.Studies show that ZIF-67 samples cored on Co and ZIF-8 samples cored on Zn possess uniform structure and ZIF-67 has better catalytic performance as well as higher KA selectivity.By the reaction results and analysis of different characterization methods,such as XRD?BET ?SEM and so on,we compare the differences between the two ZIF-67 samples of which one is prepared by rapid mixing method at room temperature and the other is prepared by solvothermal method respectively,in the structure and catalytic performance.When ZIF-67 was used as catalyst in liquid cyclohexane oxidation,it dispersed in the reaction liquid and turn into micro flocs,which leads to recycle difficulties.Therefor,to further improve the structure stability of the material and to make it convenient for recycling,we add structurally stable carbon nanotubes to prepare ZIF-67@CNTs,a novel composite material.Comparing the ZIF-67 samples of which one is prepared by mechanical mixing method and the other is prepared by in-situsynthesis method,SEM characterization finds that the boundary of CNTs and ZIF-67 is well-defined in sample prepared by mechanical mixing method,while the two materials combine more closely in sample prepared by in-situ synthesis method.What's more,study finds that the composite material ZIF-67@O-CNTs prepared by O-CNTs which was pretreated in a mixture of concentrated acids(the volume ratio of nitric acid and sulfuric acid is 1:3)has more regular structure than that prepared by original CNTs without any pretreatment.When the composite material ZIF-67@OCNTs is observed under the scanning electron microscopy(SEM),it clearly shows that tiny carbon nanotubes cover on the regular crystal face of ZIF-67 without clusters of O-CNTs.And at the same time,this work studies the influence of different addition amounts of O-CNTs on structure of the composite material.The experiments find that ZIF-67@O-CNTs has good catalytic performance as well as high KA selectivity in the reaction of liquid cyclohexane oxidation,and the catalyst could also be recycled efficiently after reaction.