Design And The Performance Study Of Novel Porous Catalysts For The Synthesis Of 5-hydroxymethylfurfural And 2,5-furanedioic Acid From Biomass Monosaccharide

With the rapid development of modern society,the excessive consumption of non-renewable fossil resources such as oil,natural gas and coal has led to serious environmental pollution and global climate change,which has aroused people’s great attention to the use of renewable resources to replace traditional resources.Biomass is the most abundant renewable resource on the earth,so the preparation of high value-added chemicals from biomass resources has important research significance.Among the many biomass-based chemicals,5-hydroxymethylfurfural（HMF）is a key bio-based platform molecule that can generate many useful organic chemicals through oxidation,hydrogenation,polymerization and ring-opening reactions.2,5-furandicarboxylicacid（FDCA）,a derivative of HMF,has been identified by the U.S.Department of Energy as one of 12 priority compounds for building a"green"chemical industry of the future,with potential applications in pharmaceuticals,polymers,fine chemicals and other fields.Therefore,the efficient synthesis of HMF and FDCA is of great significance to the development of social economy and ecological environment.At present,chemical catalysis is the main method for the conversion of biomass monosaccharide to HMF and further oxidation to FDCA.The key to achieve high yield HMF and FDCA is to construct efficient catalytic system,among which,the development of new catalysts is the core of the design of efficient catalytic system.Porous catalysts have been widely used in the field of catalysis due to their advantages of high specific surface area and porosity,small density,adjustable pore size and modified surface properties.The production of HMF from biomass monosaccharide and the oxidation conversion of HMF to FDCA involve multi-step reactions,and it is difficult for a catalyst with a single active site to obtain high reaction selectivity.Therefore,this paper is devoted to the development of a series of catalysts with hierarchical pores and multiple active sites to realize the efficient conversion of biomass monosaccharides and HMF.The physical and chemical properties of the catalyst,such as morphology,structure,thermal stability and acid-base intensity,were analyzed by systematic characterization.And through the catalytic experiment to explore the key factors affecting the catalyst activity,summarize the catalytic law and reaction mechanism.The specific research content is as follows:（1）Preparation of Mesoporous SBA-15 Catalysts with Different Morphologies and Study on the Preparation of 5-Hydroxymethylfurfural by Fructose DehydrationFour kinds of SBA-15 mesoporous molecular sievers with different morphologies（long-rod、hexagonal prism、short-rod、sphere）were successfully synthesized by using Pluronic P123 triblock copolymer and co-surfactant（CTAB）as structure guiding agent.They were named LR-SBA-15,HP-SBA-15,SR-SBA-15 and SP-SBA-15.The four morphologies of SBA-15 were treated by grafting sulfated zirconia（SZ）layer by layer to obtain a series of SZ@SBA-15 solid acid catalysts.Among them,2SZ@SBA-15catalyst has the largest surface acidity and the best Br（?）nsted/Lewis acid ratio.Mg was loaded on the SZ@SBA-15 catalyst by wet impregnation,which increased the basic sites of the catalyst.The results showed that the short rod SR-2SZ@Mg-SBA-15 had a large specific surface area(744 m² g^-1)and the best acid strength(1.74 mmol g^-1)and basic strength(1.35 mmol g^-1).The four morphology 2SZ@Mg-SBA-15 solid catalysts were applied to the i Pr OH/DMSO co-solvent system to catalyze fructose,and 92.7%HMF yield was obtained.The catalytic results showed that the morphology and mesoporous channels of SBA-15 played an important role in the catalytic performance of the catalysts.The activity sequence of these catalysts was as follows:Long rod catalyst（LR-2SZ@Mg-SBA-15）<Hexagonal prism catalyst（HP-2SZ@Mg-SBA-15）<Spherical catalyst（SP-2SZ@Mg-SBA-15）<Short rod catalyst（SR-2SZ@Mg-SBA-15）.The catalytic activity of the catalyst SR-2SZ@Mg-SBA-15 did not change significantly after being used for fifth times,indicating that the catalyst has good reproducibility.In addition,we found that not only Br（?）nsted/Lewis acidic sites,but also basic sites are conducive to the dehydration of fructose to produce HMF.In this work,we developed mesoporous SBA-15 catalysts with different morphologies and acid-base bifunctions,which provided a new direction for the realization of efficient catalytic synthesis of fructose HMF.Using the green solvent i Pr OH to replace part of DMSO can reduce the harm to the environment.Therefore,this work provides a general strategy for the development of green catalytic system,rational utilization of biomass resources and environmental protection.（2）Pickering HIPEs template method to construct hierarchical pore nitrogen-doped carbon catalyst for glucose conversion to 5-HydroxymethylfurfuralUsing oleic acid modified SBA-15 as a stabilizer to stabilize the water-in-oil（W/O）Pickering HIPEs,DVB and 1-vinylimidazole were thermally polymerized in the Pickering template to obtain nitrogen-containing Poly（HIPEs）.Carbonization and sulfonation prepared hierarchical pores,acid-base bifunctional nitrogen-doped carbon catalyst（SNC）.By changing the parameters of Pickering HIPEs,the porous structure of the catalyst can be adjusted.By changing the ratio of DVB and 1-vinylimidazole and different carbonization temperatures,the nitrogen content and nitrogen form of the catalyst（pyridine nitrogen,pyrrole nitrogen and graphite nitrogen）can be adjusted.The results of the catalytic reaction showed that the pyridine nitrogen provided the main basic site for the glucose isomerization process,and the sulfonate group provided the main Br（?）nsted acid active site during the fructose hydrolysis process.The prepared acid-base bifunctional,hierarchical pore catalyst was used for one-pot catalytic conversion of glucose to HMF.Among them,the catalyst SNC2-700 has a large specific surface area(268 m² g^-1)and the best acidity value(2.35 mmol g^-1)and basicity value(3.02 mmol g^-1).Under the optimum reaction conditions,the yield of HMF from glucose was 61.3%.In addition,SNC2-700 can be recycled in the same catalytic system for four cycles,and the catalyst still has good catalytic activity.This work provides a general strategy for the development of nitrogen-doped carbon catalysts with hierarchical pore structure for the efficient conversion of carbohydrate compounds to platform chemicals.（3）Pickering HIPEs template method to construct Co O_x-HPC（hierarchical porous carbon）supported Au Pd catalyst for efficient catalytic oxidation of HMF to FDCAPoly（HIPEs）was synthesized by Pickering HIPEs template method,the cobalt salt was uniformly dispersed in Poly（HIPEs）by wet immersion method,and Co/Poly（HIPEs）was calcined at different temperatures to obtain the hierarchical porous carbon support（Co O_x-HPC）doped with polyvalent cobalt（Co O_x）.The hierarchical pore Au Pd/Co O_x-HPC catalyst was prepared by sol-immobilization loading Au Pd bimetallic onto Co O_x-HPC surface.Au nanoparticles are easy to inactivate during the selective oxidation process of HMF.The active interface formed by supporting alloyed Au Pd on the reducible metal cobalt oxide can effectively solve this problem.The Co O_x-HPC carrier synthesized by Pickering HIPEs method has improved the catalytic activity of the catalyst due to the uniform dispersion of cobalt oxide（Co O_x）on the hierarchical porous carbon material.Among the prepared series of catalysts,Au₂Pd₁/Co O_x-HPC has a larger specific surface area(228 m² g^-1)and the best ratio of Au/Pd.showing the best activity in the catalytic conversion of HMF reaction,and obtaining 97%FDCA yield.The reaction process was analyzed by kinetic calculation,and it was confirmed that the oxidation of FFCA to FDCA was the rate-determining step of this reaction.Finally,a cycle experiment was performed on the synthesized catalyst,and there was no significant loss of activity after repeated use for four cycles.This study provides an efficient,cost-saving and environmentally friendly catalytic system for the production of FDCA by HMF,and highlights the great potential of using Pickering HIPEs method to synthesize hierarchical carbon as a carrier for the preparation of highly active catalytic systems.