Preparation Of Cobalt@N-doped Carbon Materials And Their Application For Oxidative Esterification Of 5-hydroxymethylfurfural

Nitrogen-doped carbon materials have attracted more and more attention due to their adjustable pore size and high surface area.Loading cobalt on the nitrogen-doped carbon materials not only enhances the activity of the catalytic reaction,but also improves the dispersibility and stability of the metal sites.Therefore,it is a great significance to synthesize cobalt/nitrogen co-doped carbons by green and simple methods and use it as catalyst in heterogeneous reactions.In this thesis,cobalt/nitrogen co-doped carbons were prepared by one-pot pyrolysis of chitosan and Zeolitic imidazolate frameworks(ZIFs)respectively.And their reactivity in the oxidative esterification of HMF were studied.The research contents are as follows:First,using chitosan as a precursor,the corresponding cobalt/nitrogen co-doped carbons are synthesized by high-temperature carbonization of chitosan.The oxidative esterification of 5-hydroxymethylfurfural(HMF)using these materials as a catalysts was studied.Among them,the optimal reaction conditions are as follows:using Me OH as solvent,O₂ as oxidant at 50?under atmospheric pressure for 24 h giving the product up in good yield(94%).Through the recovery test,it is found that the system can be recycled 4 times without losing activity,guaranteeing the possibility of large-scale production.At the same time,studies have shown that the high surface area caused by the partial evaporation of zinc in the precursor and the increase in Lewis basic sites and the decrease in strong Lewis acid sites caused by the residual zinc in the catalyst also ensure the higher catalytic performance of the catalyst.Secondly,the application of catalysts prepared with amine-modified ZIFs in the oxidative esterification of HMF was explored.The influence of the type of amine on the morphology and particle size of ZIFs was studied.And the particle size of ZIFs modified with aniline was the smallest.Through experiments and calculations,it is found that the synergistic effect produced by the electronic interaction of Co N_x sites and Co nanoparticles(Co NPs)also improves the activity of the catalytic reaction.The optimal reaction conditions are as follows:using Me OH as solvent,air as oxidant at room temperature under atmospheric pressure for 48 h giving the product up in good yield(93%)).At the same time,the catalyst can be used repeatedly for 6 times without affecting its catalytic activity.