Synthesis Of Cobalt Zeolitic Imidazolate Framework Derived Co-N-doped Porous Carbon For Tandem Catalysis

As a new type of inorganic-organic porous crystalline hybrid materials,metal-organic frameworks(MOFs),composed of metal atoms/clusters and organic ligands through coordination bonds,have demonstrated potential applications in many fields,such as gas adsorption and separation,proton conduction,drug delivery,heterogeneous catalysis,etc.Besides,the periodic structure renders MOFs good templates for the preparation of porous carbon materials through pyrolysis at high temperature.In the process of pyrolysis in an inert atmosphere,although the original structures of MOFs are destroyed,the specific surface area and pores can still be partially inherited,thus providing porous carbon composites with high specific surface area,which further expands the scope of application of MOFs.Aromatic and aliphatic amines have a wide range of applications in the industry.In general,the amines can be prepared by the hydrogenation of corresponding nitro compounds.In order to prevent the hydrogenation process from affecting other reducible functional groups,the selectivity of the reaction is very important.However,at present,selective hydrogenation is still largely dependent on the expensive noble metal catalysts,and there is an urgent need for catalysts based on inexpensive transition metals.At the same time,in order to improve the efficiency of the reaction,in situ generation of hydrogen instead of using hydrogen gas with a low solubility should be a good idea,in which the in situ generated hydrogen can have contact with the substrate directly,thereby improving the reaction efficiency.In this case,ammonia borane,with a high hydrogen content of 19.6 wt%and good solubility,is an excellent choice.Therefore,the dehydrogenation of ammonia borane coupled with the hydrogenation of nitro compounds should be a good way to improve the reaction rate.We choose a classic MOF,cobalt zeolitic imidazolate framework ZIF-67 as the template and the precursor to prepare the Co-CoO@carbon nanocomposite catalyst.Specific characterization shows that the catalyst is composed of Co nanoparticles with oxidized CoO on the surface,which are uniformly distributed in the N-doped porous carbon.This MOF-derived catalyst exhibits great activity and recyclability in the tandem reaction of the dehydrogenation of ammonia borane and the hydrogenation of nitro compounds at room temperature.Compared with 1 bar hydrogen,the efficiency of the tandem reaction is several orders of magnitude higher.In addition,the catalyst can also selectively convert various aromatic and aliphatic nitro compounds with different substituents into corresponding amines,and the reaction can be carried out in a few hours with conversion and yield up to 100%.At the same time,for substrates containing other reducing groups(including nitriles,aldehydes and ketones),the catalyst ensures that this reducing functional groups are not affected by the hydrogenation.