| Catalytic oxidation of cyclohexane to cyclohexanol and cyclohexanone(KA oil)is one of the most important reactions in the field of saturated C-H oxidation.Two organic chemical raw materials,cyclohexanone and cyclohexanol,are the key to the effective synthesis of new materials and other chemicals.At present,the main problem of cyclohexane oxidation is that the C-H bond is difficult to activate,and the product KA oil is easy to be deeply oxidized,and it cannot guarantee both high conversion and high selectivity.In response to these problems,this paper chose cobalt as the active metal to develop a new type of nitrogen-doped carbon material.To explore the effect of nitrogen doping on the catalytic performance of two different materials for the oxidation of cyclohexane,one type is MOF material with a specific coordination structure,and the other is a traditional supported material.The experiment found that the introduction of nitrogen can effectively improve the catalytic activity of the two materials,and study the effect of nitrogen doping on the catalytic performance of the catalyst for cyclohexane oxidation.In this work,Co-MOF materials were prepared by hydrothermal method,which was used as a template agent to prepare nitrogen-doped cobalt-based carbon materials by pyrolysis.Triethylenediamine was used as the nitrogen source.Influence of material catalytic performance.The study found that nitrogen doping has no effect on the structure of the material.The experimental results show that nitrogen doping can significantly improve the catalytic performance of the catalyst for the catalytic oxidation of cyclohexane.The catalysts were analyzed by XRD,XPS,TEM,BET and other characterization methods,and it was found that due to the poor thermal stability of triethylenediamine,the amount of nitrogen doping was small,and it was found that the metal inside the material was evenly dispersed after high temperature calcination.Next,this work designed a cobalt-supported nitrogen-doped graphene material(Co-N-r GO)co-doped with graphene oxide as the carrier.The effects of different preparation methods,loading capacity,and roasting temperature on the catalytic performance of cyclohexane oxidation were investigated,and the effect of nitrogen doping on the catalytic effect was studied.It was found that the metal can coordinate with nitrogen and the undoped nitrogen phase It is more uniformly dispersed than metal,which successfully solves the disadvantages of traditional supported catalyst active metals that are easy to agglomerate;at the same time,it is more beneficial to form a carbon film on the metal surface after nitrogen doping.The metal particles are wrapped by the nitrogen carbon film to prevent metal loss and improve Catalyst stability;experiments also found that nitrogen doping can promote the decomposition of cyclohexyl hydrogen peroxide(CHHP).The experimental results show that the catalytic material has high catalytic activity in cyclohexane catalytic oxidation reaction,the conversion rate of cyclohexane is 8.85%,the selectivity of KA oil reaches 85.73%,and the catalyst is reacted for 5 times without deactivation.Finally,in order to further study the effect of nitrogen doping on the oxidation of cyclohexane from a theoretical perspective,the Co-N-r GO material was modeled and simulated.After(4,4)single-layer graphene sheet was doped with nitrogen and then cobalt was loaded,six models were selected after structural optimization,and the Muliken charge distribution and charge density analysis were carried out.The study found that after nitrogen doping,it can increase the surrounding carbon The charge density indicates that cobalt and nitrogen work together to increase electron transfer.By absorbing CHHP on the surface of the catalytic material and optimizing the calculation,it was found that the introduction of nitrogen can lengthen the bond length of the O-O bond in CHHP,indicating that nitrogen doping is beneficial to the decomposition of CHHP. |
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