Study On Organic-metal Complexes Derived Carbon Supported Metal Catalysts And Their Catalytic Conversion Of Glycerol

The rapid development of biodiesel industry is driven by the rising international crude oil price and increasingly severe environmental problems.The production of biodiesel is accompanied by the production of a large amount of glycerol.The excess supply of glycerol in the market also leads to a large waste of resources.The market price of glycerin carbonate,which is generated by transesterification of glycerol,or dihydroxyacetone,which is generated by selective oxidation of glycerol,is about 4-24 times that of glycerol.However,the main catalysts currently used generally have many problems,such as expensive price,fewer active sites and higher pollution.Cheap and easy to obtain biomass materials contain a variety of complex functional groups and heteroatoms,among which carboxyl and hydroxyl groups can combine with metal ions to form organic-metal complexes,and elements such as N and P in biomass materials can modify metal elements to prepare various functional carbon supported metal catalysts.Focusing on the efficient conversion of glycerol into various value-added fine chemicals,this paper expands the selection of organic ligands from inexpensive and easily available small molecules to natural macromolecules.Through the green synthesis process,the preparation and optimization of highly dispersed carbon supported metal catalysts,and studies its application in catalytic conversion of glycerol.It provides a feasible idea for industrial production and rapid preparation of composite catalysts with abundant pores and uniform distribution of active sites.The specific exploration contents are as follows:(1)Histidine,a small organic material,is an important coordination center for metalloproteins and one of the excellent precursors for the preparation of carbon materials.We directly assembled histidine and potassium nitrate into organic-metal complex by means of mechanical ball milling,and obtained catalyst KX@NC after carbonization at high temperature.The structure of the catalyst were analyzed by FT-IR,SEM and XRD.The performance of K2@NC in catalyzing glycerol transesterification to produce glyceryl carbonate was evaluated.The selectivity of glycerol and glycerol carbonate was 95.4%and97.5%at 100 ~oC for 2 h.The conversion and selectivity of glycerol and glycerol carbonate were still 90%after 7 times of use.Compared with traditional methods such as impregnation reduction,the preparation process of carbon supported metal catalyst derived from organic-metal complex is more simple and efficient.Histidine provides abundant O coordination,the presence of a large amount of N in melamine provides anchor sites for K~+,which is conducive to the synthesis of rich,uniform and stable K~+doped carbon materials.(2)Based on the research in the previous chapter,this chapter extends the organic ligand from small molecules to natural macromolecules.The metal-phenolic network coating strategy was combined with the carbon-loaded metal strategy in the probe reaction of glycerol selective oxidation requiring Pt-Bi bimetal co-catalysis.Tannic,a greener and cheaper biomass material,was used as carbon source and adhesive as well.Bismuth-polyphenol network was constructed on the surface of Si O2.After carbonization at high temperature,precious metal Pt was loaded to obtain catalyst Pt/Bi X-C@Si O2.The structure of the catalyst was characterized by FT-IR,TEM,XPS and other characterization tests.The performance of the Pt/Bi2-C@Si O2 in secondary hydroxyl oxidation of glycerol was evaluated.At 60 ~oC for 6h,85.8%glycerol conversion and 90.2%dihydroxyacetone selectivity were obtained.The introduction of Si O2 as template makes the polyphenol network coating have good structural stiffness after carbonization and the metal-polyphenol network of the second layer limits the active center during carbonization.Porous carbon shells with good structural stiffness and rich Bi sites can be used as efficient and stable carriers of Pt NPs to modify the electrons on the catalyst surface,effectively alleviating the problems of bimetallic active site agglomeration coverage.(3)In order to continuously increase the commercial economic benefit and atomic efficiency,we added nitrogen source to the metal-phenolic network formed by mechanical ball milling without adding template agent.The carbon and nitrogen skeleton of monatomic Bi doped with high content x Bi@NC(content:2.57 wt%)was obtained by calcination,Pt NPs was dispersed on the new carbon supported metal carrier.The carbon composite catalyst Pt/x Bi@NC was obtained,which realized the unique assembly of Pt NPs and ultra-stable single atom Bi.Under mild conditions(30 ~oC,1 atm air),the conversion of glycerol to Pt/0.1Bi@NC was 86.8%and the selectivity of DHA to Pt/0.1Bi@NC was 87.0%.The adsorption configuration of glycerol on the bimetallic site was analyzed in depth with theoretical calculation,and the unique advantages of the new bimetallic configuration in the reaction process were analyzed.In Pt/0.1Bi@NC,the assembly of Pt NPs and Bi promoted the chelation of Bi with the secondary hydroxyl group of glycerol,which accelerated the oxidation of the secondary hydroxyl group in glycerol and required a lower energy barrier to produce DHA.