Preparation And Application Of Cobalt Based Nitrogen-Doped Carbon Catalysts

The catalysis plays a core role in the modern chemical industry,and the development of new high-efficiency catalysts has been an important topic of catalytic research.The homogeneous catalysts based on noble metals,the use of expensive metals,the homogeneity and cumbersome separation process of the reaction limit their applications.Non-noble metal based heterogeneous catalysts were created,due to their low cost,easy separation and reusable use in industrial applications.The carbon material is often used as a carrier of heterogeneous catalyst due to its high surface area,adjustable porosity.Compared with the pure carbon material,the introduction of nitrogen can adjust its physical chemical properties,enhance metal-support interaction,thereby exhibiting excellent properties in catalytic reactions.In order to broaden the nitrogen-doped carbon supported transition metal catalyst in the field of heterogeneous catalyst,three nitrogen doped carbon supported cobalt catalysts were prepared by different methods,and were applied to hydrogenation and oxidation reactions.Excellent catalytic performances were obtained in the reaction.（1）Single-atomic catalysts are considered to be a bridge between heterogeneous and homogeneous catalysis,and we have converted the homogeneous cobalt complex into cobalt single atoms by adsorption and pyrolysis process on dendritic silica nano microspheres.The cobalt atoms are anchored at a nitrogen-doped ultrathin nanocarbon film.A large amount of nitrogen atoms in the precursor of the 1,10-Phenanthroline monohydrate could be coordinated with cobalt ions,leading to the formation of Co-N_x sites in the carbon material.At the same time,the rich nanofold in the silica nano microspheres increased the initial spatial distance between cobalt atoms,thereby preventing agglomeration of them in the pyrolysis process.The catalyst has excellent catalytic activity and selectivity towards the oxidative dehydrogenation of saturated N-heterocycles and transfer hydrogenation of unsaturated N-heterocycles under base-free conditions.（2）In addition,we have prepared another cobalt single atom catalyst with Co-N₄ active sites by pyrolyzing bimetallic Zn Co-ZIF precursor,and the catalysts show excellent activity towards the transfer hydrogenation between saturated N-heterocycles and nitroaromatic compounds in aqueous solution.The reaction process is green,efficient.The hydrophobicity of the catalyst facilitates high adhesion of organic substrates and removal of the by-product water from the surface of catalyst,and the catalytic activity is higher than the reported catalysts for the reaction.The DFT calculation and controlled experiments revealed that the strong interaction between Co-N₄sites and substrates could efficiently catalyze the dehydrogenation of 1,2,3,4-tetrahydroquinoline for the reduction of nitrobenzene.（3）In order to further expand the application of nitrogen-doped carbon supported cobalt catalysts,we have prepared a series of nitrogen-doped carbon supported cobalt catalysts with low-cost dicyandiamide,glyoxal and cobalt nitrate.The catalysts are applied to selectively oxidize the alcohol to the high value-added ester and carboxylic acid under air,and exhibit extensive applicability in the oxidation of various aromatic and aliphatic alcohols.This paper can provide new ideas for the construction of nitrogen doped carbon material supported transition metal based catalysts to challenging and high value-added reactions.In addition,the mechanisms of the two oxidation reactions are discussed in detail via the controlled experiments and characterizations:both of the reactions have the process of benzyl alcohol→benzaldehyde→hemiacetal,and benzyl alcohol→benzaldehyde is the rate-determining step.