Study On The Preparation Of ZIFs Derived Cobalt-based Nitrogen Carbon Composites And Their Catalytic Performance In The Hydrogenation

Zeolitic Imidazolate Frameworks?ZIFs?have a unique structure similar to zeolite molecular sieves while possessing the excellent properties of the MOFs material itself.Derived materials obtained by high temperature pyrolysis using ZIFs as a template not only partially inherit the structure and advantages of the parent ZIFs,but also expose more active sites of metal,and also greatly improve the stability.Therefore,it has attracted widespread attention in catalysis.In this paper,ZIFs crystal materials containing metal,nitrogen and carbon were selected as self-sacrifs templates to prepare high-efficiency nitrogen-doped carbon materials coated Co hydrogenation catalyst for liquid phase catalytic hydrogenation of aromatic nitro compounds to aromatic amines.The activity of the catalyst was investigated by liquid phase catalytic hydrogenation of nitrobenzene as probe,and the structure-effect relationship of the catalyst was studied in combination with catalyst characterization.In this paper,ZIF-67 material with regular structure,uniform particle size and specific rhombohedral polyhedral structure was successfully prepared by simple room temperature stirring method.Then,it was pyrolyzed at a high temperature to obtain corresponding derivatized Co@NC hydrogenation catalyst under the protection of N₂.It was found by characterization that the prepared Co@NC hydrogenation catalyst inherits the structure and properties of the template ZIF-67 to some extent,and the Co@NC hydrogenation catalyst obtained by ZIF-67 pyrolysis was nitrogen-doped graphite carbon-coated cobalt nanoparticle structure.The prepared derivative material was used for hydrogenation of nitrobenzene,and the result showed that the derivative material Co@NC-800 pyrolyzed at 800?had the best hydrogenation activity under T=90^oC,P_H2=2.0MPa,the yield of aniline was over 99%after 4h of the reaction.Combined with the catalytic performance and characterization results,the high catalytic activity of Co@NC-800 catalyst might be derived from the effective synergy between the nitrogen-doped graphite carbon layer and the metal cobalt nanoparticles.Based on the research of Co@NC catalyst,ZIFs materials?BMZIFs?containing both cobalt and zinc metals were also prepared by room temperature stirring,and then subjected to high temperature pyrolysis under N₂ protection to obtain a Zn-doped Co-Zn@NC hydrogenation catalyst.The characterization results showed that the crystal structure,morphology and isothermal adsorption curves of BMZIFs with different Co/Zn ratios were basically identical,but the introduction of Zn had a great influence on the particle size and thermal stability of BMZIFs,and the specific surface area of the derivative material increases as a large number of pore structures left by evaporation of Zn during pyrolysis.In addition,the Co-Zn@NC hydrogenation catalyst obtained by pyrolysis of BMZIFs were still a nitrogen-doped graphite carbon-coated cobalt nanoparticle structure,and the addition of Zn was beneficial to prevent the agglomeration of elemental Co during pyrolysis.Therefore,compared with the prepared Co@NC catalyst,xCo-yZn@NC derived from xCo-yZn-BMZIFs exhibited more excellent catalytic hydrogenation activity in the catalytic reaction.Among them,2Co-1Zn@NC-900 obtained by pyrolysis of 2Co-1Zn-BMZIF as a precursor at 900°C had the best catalytic hydrogenation activity.After 2h reaction,the yield of aniline can reach more than 99%under T=80^oC,P_H2=1.0MPa.