Preparation And Catalytic Performance Of ZIFs-derived Carbon-based Nanocomposites

Heterogeneous catalysis plays an important role in chemical an d energy fields.More than 90%of all chemicals are produced with solid catalysts（Calculated by volume）.Carbon material has the advantages of wide source,low density,stable structure,and low-cost,is an ideal heterogeneous catalyst.Despite these advantages,the catalytic activity of unmodified pure carbon materials is very low,and there is still a big gap compared to homogeneous catalysts and other heterogeneous catalysts.Therefore,the design of novel and efficient carbon-based nanomaterials and their application in organic synthesis reactions is one of the research hotspots in the field of catalysis.Zeolitic imidazolate frameworks（ZIFs）have large specific surface area,high porosity,and adjustable structure,which can be used as a precursor for preparing carbon materials.We developed several ZIFs derived carbon-based nanocomposites from the perspective of structural morphology,pore size distribution and the design of active ingredients,and studied their applications in biomass conversion and various organic synthesis reactions.Firstly,to avoid sintering and metal agglomeration that often occur in the calcination process of ZIF-67,zinc was introduced into the ZIFs structure to increase the cobalt atomic spacing,prevent agglomeration,and improve the porosity of carbon materials.Cobalt nanoparticles embedded in N-doped porous carbon（Co@CN）were prepared by the pyrolysis of bimetallic zeolitic imidazolate frameworks（BMZIFs）.The catalyst shows excellent catalytic efficiency in one-pot selective oxidative cleavage of different linkages likeβ-O-4,a-O-4,andβ-1 in organosolv lignin and lignin model compounds in the presence of oxygen（ambient pressure）under mild conditions（383 K）.The catalytic system is also suitable for the cracking of organosolv lignin,which can be decomposed into a series of small-molecule phenols and ketones.Ester furan-2,5-dimethylcarboxylate is an important building unit for the synthesis of bio-polyethylene furanoate to replace polyethylene terephthalate plastic.Therefore,we designed a hollow-yolk-shell Co@CN material for the oxidative esterification of5-hydroxymethylfurfural to synthesis furan-2,5-dimethylcarboxylate.The catalytic system uses environmentally friendly and naturally abundant atmospheric oxygen a s the oxidant to achieve efficient base-free catalyzed oxidative esterification of5-hydroxymethylfurfural at 80℃under high concentrations（2 M）.The Si O₂ acts as a protective shell to prevent the agglomeration of ZIF-67 during pyrolysis.Porous carbon shells derived from ZIF-8 proves to facilitate mass transfer of the active component and protect the catalytic active sites to avoid leaching.Subsequently,the application of ZIFs derived porous carbon load cobalt nanoparticles in organic synthesis reaction was explored.We developed a facile and effective in-situ doping-carbonization method to fabricate highly porous N,P co-doped carbon materials embedded with tiny Co NPs（Co@NCP）by thermolysis of bimetallic zeolitic imidazolate frameworks.Ammonium phosphate nanospheres are not only the sacrificial templates to form porous structure,but also the phosphorus source of the carbon material.The obtained porous Co@NCP exhibits high performance in the base-free hydrogen auto-transfer synthesis of quinoxalines from diols and o-nitroanilines in toluene at 140℃.Moreover,the porous carbon load cobalt nanoparticles derived from ZIFs was successfully applied in primary alcohol ammoxidation reaction.A cobalt catalyst derived from a unique core-shell structure based on hollow ZIF-8 and ZIF-67was prepared,which exhibits excellent catalytic efficiency for the synthesis of nitriles from alcohols in water under mild conditions（1 atm O₂,50°C）owing to its large BET surface area,high pore volume,high basicity,and hydrophilicity.This reaction uses water as solvent,which has the advantages of environmental friendliness,non toxicity and low price,and conforms to the principle of green chemistry.On the one hand,iron is abundant and cheaper than cobalt.On the other hand,the single atom catalyst has the advantage of atomic dispersion and high atom utilization.Therefore,the iron single atom catalyst derived from ZIFs was successfully synthesized and applied in hydrogenation reaction of nitrobenzene and primary alcohol ammoxidation reaction.Firstly,aniline was used as an additive to modify the structure of Fe-ZIFs precursor.Then,the modified Fe-ZIFs was calcined at 900℃to obtain iron single atom catalyst.The as-prepared catalysts exhibit superior catalytic activity and selectivity on the hydrogenation of nitroarenes(TOF up to 1727 h^-1)at room temperature with a broad substrate scope.Moreover,we also designed and prepared a nitrogen-doped porous carbon-supported iron single-atom catalyst and investigated its application in the ammoxidation of primary alcohols.Benzylamine as crystallization modulators proved to be essential to tune the morphology and size of ZIFs re sulting in uniform and smaller particles.The optimal catalyst Fe₁-N-C achieves an efficient synthesis of various aryl,heterocyclic,allylic,and aliphatic nitriles from alcohols in water under very mild conditions.Moreover,the catalyst can be easily recycled and reused without significant loss in activity.Six catalytic systems based on ZIFs derived carbon nanocomposites were established for biomass conversion and organic synthesis.By using different methods to modify the ZIFs precursors,the electronic structure of carbon-based nanocomposites is optimized,the structure and morphology are controlled,and the size of metal nanoparticles is reduced,thus improving the catalytic activity in biomass conversion and organic synthesis.The designed porous carbon nanomaterials have excellent catalytic activity,which highlights the great potential value of porous carbon materials in the field of heterogeneous catalysis.