Mechanism Study On Catalytic Hydrogenation And Oxidative Esterification Of 5-Hydromethylfurfural

5-hydroxymethylfurfural（HMF）has emerged as an important platform chemical to degrade lignocellulosic biomass into valuable chemicals and fuels such as 2,5dihydroxymethylfuran,2,5-dimethylfuran,2,5-furan dicarboxylic acid（ester）,γvalerolalactone.So far,numerous studies focus on the transformation of HMF over earth-abundant 3d metal catalysts,but there are numerous issues such as low efficiency,low selectivity,harsh reaction condition,or complex reaction system.Previous studies have demonstrated that nitrogen-doped carbon materials can significantly enhance metal dispersion,change metal electronic structures,and tune the interactions between metal catalysts and substrates/intermediates,thereby directionally improving catalytic performance.Therefore,it’s of great significance to develop novel 3d metal/nitrogendoped carbon materials for the catalytic conversion of HMF and to reveal the relationship between catalytic activity and reaction performance.This thesis takes HMF as the research object,a series of 3d metal/nitrogen-doped carbon materials were developed for the oxidative esterification and reduction of HMF for the preparation of polymer monomers furan-2,5-dimethylcarboxylate（FDMC）and 2,5-dihydroxymethylfuran（DHMF）,and the catalytic active sites and reaction mechanism of specific reactions are discussed in detail.To solve the limit of HMF oxidative esterification relying on noble metal catalysts and mixed catalyst systems,ZIF-67 derived Co@C-N material was reported to be a highly effective catalyst for the selective conversion of HMF into FDMC in 95%yield.The high activity of the Co@C-N can be attributed to the electron transfer between nitrogen-doped carbon shells and Co nanoparticles.The appropriate graphitic N and pyridinic N doping increase the electronic mobility and active sites.DFT simulations indicated that oxygen,HMF and methanol molecules are adsorbed and activated on CN materials.Furthermore,no DFF was captured as an intermediate because the oxidative esterification of aldehyde preferentially occurred than the oxidation of hydroxyl group in HMF.We anticipate that these results can drive progress in the biobased polymers sector and oxidative esterification reaction.A low-cost and sustainable cobalt/nitrogen-doped carbon catalyst（Co/Co-N/CN）containing both metallic Co and Co-N components was developed to solve the problems of expensive precursors and harsh oxidative esterification conditions of traditional Co/nitrogen-carbon catalysts.The catalyst exhibits satisfying activity for the oxidative esterification of 5-hydroxymethylfurfural and other investigated alcohols in methanol without the base additive under mild conditions.Experimental results show that an appropriate ratio of Co to Co-N is responsible for the high activity of the Co/CoN/CN catalysts towards oxidative esterification.Theoretical computational results demonstrate that the Co/Co-N group synergistically promotes electron transfer from the Co adatom to the surface oxygen atoms,facilitates O₂ adsorption and activation on the Co sites,and further reduces the energy barrier for the oxidation of alcohols to aldehydes,all of which contribute to the overall activity of oxidative esterification of alcohols to the corresponding esters.In addition to exhibiting superior intrinsic activity,the as-prepared Co/Co-N/CN catalyst also shows excellent stability and recyclability.Manganese catalyzed transfer hydrogenation of aldehydes is an attractive method for the synthesis of alcohols.A novel and efficient MnO@C-N catalyst was reported for the transfer hydrogenation（TH）of biomass-derived 5-hydroxymethylfurfural and other aldehydes to alcohols in high yields.Catalytic experimental studies showed that the MnO and nitrogen-doping are responsible for the high selectivity and high conversion,respectively.Isotopic labeling experiments demonstrated that the CTH of aldehydes to alcohols over MnO@C-N is via a route by direct hydrogen transfer.Kinetic studies revealed that N-doping can improve the reaction rate and reduce the activation energy of the aldehydes conversion.DFT calculations also indicated that both pyridine N and pyrrolic N doping can reduce the energy barrier for acetone desorption by the interaction between N and hydroxyl-H of alcohol.Furthermore,MnO@C-N showed good recyclability for at least five reaction cycles.We anticipate that these results can drive progress in the manganese catalyzed transfer hydrogenation reaction.HMF transfer hydrogenation suffers from low efficiency and relying on isopropanol.A single-atom Ni-N₄ site doped carbon catalysts was builded and bring high activity and selectivity for the reduction of hydroxymethyl-functionalized aldehydes/ketones using renewable and nontoxic ethanol as the hydrogen source.When biomass-derived 5-hydroxymethylfurfural was used as the substrate,a TOF value of 22 h-1 for the as-prepared catalyst was achieved.Experiments and simulating computation revealed that pyridinic N of the Ni-N₄ site is the active center and the presence of single-atom Ni reduces the electron density of its coordinated pyridinic N and thus achieves the high catalytic activity,demonstrating the possibility of catalytic TH reactions over metal-free sites.