Photocatalytic And Electrocatalytic Reduction Of Carbon Dioxide By Binuclear Rhenium Complexes

The demand for energy is growing all over the world.As the main energy source,non-renewable fossil fuel is faced with the problems of energy crisis,environmental pollution and greenhouse effect.According to statistics,the global atmospheric carbon dioxide（CO₂）concentration in 2021 has exceeded 417ppm,has seriously affected and threatened the human survival of the earth’s environment.Therefore,the study of CO₂conversion and utilization and the exploration of a sustainable energy conversion strategy are urgent technological challenge and problem to be solved.In recent years,transition metal molecular homogeneous catalysts have shown high efficiency in catalytic reduction of CO₂,which has attracted much attention from researchers.Rhenium bipyridine complexes,as noble metal catalysts,have the characteristics of strong catalytic activity,high durability and high selectivity in CO₂reduction,and have become the focus of research.The conjugate properties of the bipyridine ligands optimize the electron transport process and stabilize the formation of active intermediates.It has special chelating ability and coordination energy with the transition metal to effectively stabilize the low state of the transition metal.The structure and properties of bipyridine complexes can be accurately regulated through the design of molecular structure and functional modification.In recent years,there have been many reports on the production of gaseous product CO by photo/eletrocatalytic reduction of CO₂with metal complexes,and the turnover number and selectivity of CO are very high.However,most of the reports about the liquid formic acid are in the predicament of low conversion number and low selectivity.In order to solve the problem,the performance of photo/eletrocatalytic reduction of CO₂was investigated in this paper with the binuclear rhenium complex as the main research object.The thesis mainly includes four chapters.The first chapter is the introduction,which mainly introduces the structure and thermodynamic properties of CO₂molecules,and summarizes the latest research progress of photo/electrocatalytic reduction of CO₂with binuclear rhenium complexes and other binuclear metal complexes.The second chapter is about synthesis and characterization,which mainly describes the application of organic synthesis and coordination chemistry theory in practical experiments,and summarizes the coupling reaction types of transition metal C-C bonds.A rigid xanthraxene ligand framework was designed to conduct electrons efficiently and prevent deactivation of the metal center.Based on the mechanism of Suzuki-Miyaura coupling reaction,the dinuclear rhenium complexes cis-4-Bibpy Re₂（CO）₆Cl₂and trans-4-Bibpy Re₂（CO）₆Cl₂were successfully synthesized.The synthesis methods and characterization methods of the reagents used in the experiment are listed.The third chapter is the study on the photocatalytic reduction of carbon dioxide with binuclear rhenium complex.Through the blue light and ultraviolet light irradiation experiments,itisfoundthatthecatalyticsystemof4-Bibpy Re₂（CO）₆Cl₂/BIH/Ru（phen）₃Cl₂/H₂O has the performance of highly selective formation of formic acid,the TON is as high as 4018,the selectivity is as high as 91%.However,4-Bibpy Re₂（CO）₆Cl₂/BIH/TEA catalyzed carbon monoxide was highly selective,with the TON and TOF are up to 1160 and 1320h^-1,respectively,with the selectivity up to95%.At the same time,the two central metals of the dinuclear rhenium complex have been explored to cooperate with light absorption excitation and cyclic catalysis.The fourth chapter is the study of electrocatalytic reduction of carbon dioxide with binuclear rhenium complex.We have carried out the performance test of cyclic voltammetry and Coulomb analysis of controlled potential.By regulating the experimental components,we have explored the system of selective and efficient electrocatalytic reduction of carbon dioxide to carbon monoxide or formic acid.The Faraday efficiency and selectivity of carbon monoxide were as high as 87.41%and 90%,and that of formic acid was as high as 80.49%and 74%.The results of UV-Vis spectroscopy showed that the monuclear rhenium complex was easier to form Re-Re dimer than the binuclear rhenium complex,which proved that the xanthene ligand framework and the bimetal complex were stable molecular systems capable of efficient photocatalytic reduction of CO₂.