Co Nanoparticles Confined In Hierarchical Pores For HMF Oxidative Esterification

The high-value utilization of biomass resources is one of the important ways to solve the energy crisis and environmental problems.Biomass-derived platform molecules can be converted to value-added fuels and chemicals through chemical catalysis.Among the numerous biomass upgraded reactions,the oxidative esterification reaction of the furan-based platform molecule 5-hydroxymethylfurfural（HMF）has important research value.The product of this reaction,dimethyl 2,5-furandicarboxylate（FDE）,is one of the monomers used to synthesize biomass-based polyester plastic polyethylene 2,5-furandicarboxylate（PEF）,which is considered to be an ideal substitute for polyethylene terephthalate（PET）.Cobalt-nitrogen-carbon materilas are demonstrated to be effective for the oxidative esterification of HMF,but their catalytic performance still needs to be improved.Metal-organic frameworks（MOFs）,which are self-assembled by metal nodes and organic ligands,are typical precursors/templates for preparing transition metal carbon-based materials.The MOFs-derived cobalt-nitrogen-carbon materials have highly dispersed metal active sites,good electrical conductivity and controllable morphology,thus are widely used various catalysis reactions.Based on these premises,in this thesis hierarchical pores encapsulated Co-based nanocomposites were prepared by using Zn Co-ZIF as the precursor through a coating-pyrolysis protocol,which were used to catalyze the oxidative esterification of HMF.Besides,the relationship between the materials morphology and catalytic performance was studied.The main research contents and findings are as follows.A novel coating-pyrolysis protocol was developed for the preparation of hierarchical pores encapsulated Co-based nanocomposites.Co nanoparticles were confined within the nitrogen-doped hierarchical porous carbon skeletons containing micro-,meso-and marcopores.The synthesis was facile and effective,only involved the solvothermal self-assembling of Zn Co-ZIF precursor,subsequent coating of starch and the final pyrolysis.The as-prepared Co@NC-2-800 composite exhibited outstanding catalytic performance in HMF oxidative esterification,achieving 96%FDE yield at a complete HMF conversion with a turnover frequency（TOF）as high as 14.50 h^-1 at 80oC and 0.1 MPa O₂ in the absence of base.Besides,no obvious activity loss or structural changes were observed after six cycles of reaction.Results indicated that the coating of starch could remarkably modulate the morphology evolution during the MOF pyrolysis process.The nanoconfinement effect as well as open channels of the Co@NC-2-800could not only promote the accessibility of Co sites but also prevent them from leaching or aggregations,therefore significantly promoting the catalytic activity and durability.Additionally,the nitrogen doping in the carbon skeletons would also contribute to the high FDE selectivity.