Synthesis And Application Of Cobalt-Containing Porous Carbon Materials In Catalytic Hydrogenation Of [O]-/ [N]-Heterocyclic Compounds

Metal-based catalysts inclusive of metal oxides,metal complexes and metal elemental catalysts have been extensively studied and used to catalyze various reactions.Although homogeneous metal-catalysts were studied earlier due to their higher atom utilization and larger contact area,their disadvantages in difficult separation and recycling had made heterogeneous metal-catalysts gradually favored.In recent years,the development of high-dispersion and single-atom catalysts could also make the atomic utilization of heterogeneous catalysts comparable to homogeneous ones.As we all know,the selection of carriers in preparing heterogeneous catalysts is very important.Previous epoxy resin and oxide carriers had weak interactions with active components,which often led to the problem of leaching of active sites and further the reduction of activity of the catalysts.The discovery and application of carbon-based material carriers gradually solved those problems because of its advantages.E.g.carbon-based materials was porous and possessed larger specific surface area,the carbon atoms in different hybridized states showed different properties and the surface of carbon was easy to be modified.Selective hydrogenation is an important branch of the hydrogenation reactions,which is also a necessary step in many synthesis processes of drugs.Because of special d-orbital and suitable Gibbs free-energy,noble metals usually show excellent catalytic performance in the hydrogenation reactions,but their high cost has limited the large-scale applications.In this case,transition metals showing good hydrogenation potential have become ideal substitutes of nobale metals.Based on the above considerations,we have synthesized CoNi-CN materials and Co/C-D materials to catalyze the selective hydrogenation of[O]-/[N]-heterocyclic compounds,for which the satisfactory results have been obtained.The specific research contents are as follows:1.The CoNi-ZIF-P123 precursor was synthesized under stirring at atmospheric pressure by using cobalt nitrate,nickel nitrate,P123 and 2-methylimidazole as raw materials.Subsequently,the CoNi-CN catalyst was prepared by pyrolysis process at H₂ atmosphere and applied to catalyze the hydrogenation of epoxy cyclohexane.Under the reaction conditions of 70℃,3 MPa H₂ and 6 h,97.4%of epoxy cyclohexane was converted to 94.4% of cyclohexanol.Through a series of characterizations such as XRD,FTIR,Raman,UV-vis,TG,BET,FSEM,TEM,XPS,H₂-TPR,the reasons of the excellent catalytic performance of the catalyst were revealed.The introduction of P123 made the particle size of the material more uniform,and also increased the pore size of the material to improve the mass-transfer efficiency.On the other hand,the carbon shell formed by P123 during the pyrolysis process played a key role in maintaining the structure of the materials and preventing the structure from collapse.The doping of Ni species improved the selectivity of the target product through the electronic coordination with Co species,and further changed the reduction behavior of Co species.2.By using cobalt nitrate,urea and coconut-shell charcoal as raw materials,the Co（OH）₂/C-D precursor was prepared by the dynamic precipitation method,and then the Co/C-D catalyst was obtained by pyrolysis at H₂ atmosphere.Compared with the traditional impregnation method,the addition of urea could greatly increase the loading amount of Co species;compared with the static precipitation method,the dynamic method increased the loading amount of Co species while increasing the dispersion of Co species.Thus-prepared catalyst was used to catalyze the hydrogenation of quinoline,in which 100% conversion of quinoline and 100% selectivity of 1,2,3,4-tetrahydroquinoline was obtained under mild conditions（60℃,3 MPa H₂,7 h）.The materials were widely characterized by XRD,FSEM,TEM,FTIR,Raman,TG,BET techniques.It was found that the good catalytic performance of Co/C-D could be attributed to the high loading amount and high dispersion of Co species promoted by the dynamic precipitation method.Recycling experiments also showed that the catalyst had highly recyclable stability.