Construction Of Porous And Multi-functional Catalysts For Catalytic Conversion Of Carbohydrates To 5-Hydroxymethylfurfural And 2,5-Furandicarboxylic Acid

Traditional fossil energy represented by coal,oil and natural gas is an important pillar of national economic development.However,it is not renewable and reserves are limited.At the same time,their exploitation,processing and utilization can cause serious environmental pollution.Therefore,the development and utilization of green renewable energy is an important way for solving energy and sustainability issues.In recent years,the preparation of high value-added chemicals from renewable biomass-based carbohydrates has important research significance.Among them,5-hydroxymethylfurfural?HMF?and its derivative 2,5-furandicarboxylic acid?FDCA?have attracted extensive attention from researchers as two important platform compounds.At present,chemical catalysis is the main research method for the conversion of carbohydrates to prepare HMF and FDCA.The construction of catalytic reaction system is the key to improve the yield of HMF and FDCA.Moreover,the development and application of new catalysts is the core of the design of catalytic reaction systems.Porous catalysts are widely used in the field of catalysis because of their large specific surface area,low density,easy separation and low corrosion to equipment.At present,the production of HMF and FDCA directly from carbohydrates is insufficient,which is often manifested in a multi-step catalytic reaction with more intermediate products.Obtaining high yield of products requires high selectivity for the reaction,while porous catalysts with a single active site are difficult to achieve high selectivity.This paper is devoted to the design and preparation of a series of novel porous multi-site catalysts for the catalytic conversion of glucose,cellulose to HMF and further catalytic oxidation of HMF to FDCA.The morphology,structure,stability,and acid-base intensity of the synthesized catalysts were analyzed by systematic testing methods,and the performance of the catalysts was evaluated by catalytic conversion experiments.The specific research contents are as follows:?1?The preparation of nitrogen-doped carbonaceous catalysts with acid-base bifunctional sites for conversion of glucose to HMFThe modified halloysite nanotubes?m-HNTs?were prepared by grafted vinyl and precipitation polymerization.Subsequently,a series of nitrogen-doped carbonaceous catalysts?NCC?with acid-base bifunctional sites and typical mesoporous structure were synthesized by calcination and sulfonation of m-HNTs.Among them,the catalyst NCC-2 has the superior acidity value(1.35 mmol g^-1)and alkalinity value(1.09 mmol g^-1),which exhibited optimal performance in the conversion of glucose to HMF in 90/10 volume ratio of isopropanol and DMSO.The maximum yield of HMF obtained under the optimum reaction conditions was 62.8%.?2?Pickering HIPEs template constructed hierarchical porous solid catalyst with acid-base bifunctional active sites for the conversion of cellulose to HMFIn order to solve the problem of poor mass transfer efficiency of mesoporous catalyst in catalyzed cellulose,in this experiment,the m-HNTs with basic active sites were utilized as stablizer and employing the Pickering HIPEs template successfully synthesized hierarchical porous catalyst with acid-base bifunctional active sites.The characterization results show that the catalyst HPSC-3 has an average cross-linked pore size of 9.8?m and a mesoporous size of 5.6 nm,a total acidity of 4.11 mmol g^-1and a total alkalinity of 1.35 mmol g^-1,which exhibited optimal performance in the one-pot conversion of cellulose to HMF in ionic liquids?ILs?.The maximum yield of HMF obtained under the optimum reaction conditions was 45.6%.?3?The preparation of supported catalysts Pd/MC and their catalytic oxidation of HMF to FDCAThe MnO_x-CeO₂ mixed oxide was synthesized by co-precipitation method and used as a carrier.Then,the supported mesoporous catalyst Pd/MC was prepared by the sol-immobilization method.The catalyst 2%Pd/MC has a large specific surface area(103.5 m² g^-1)and high catalytic oxidation activity,which exhibited optimal performance in catalytic oxidation of HMF to FDCA.The maximum yield of FDCA obtained under the optimum reaction conditions was 92.5%,which further broadens the industrial application of HMF.In addition,cycle experiments show that the catalyst has superior recyclability.