Study On The Electrocatalytic Reduction Of Carbon Dioxide By Iron Porphyrin

Consumption of fossil fuels leads to a sharp increase of CO2 concentration in the atmosphere,which causes a series of environmental problems.In order to utilization of C02,scientists have developed many catalysts for CO2 electrocatalytic reduction(CO2 RR),which are divided into homogeneous and heterogeneous catalysts.and the clear active sites of homogeneous catalysts are more easier to study mechanism of CO2 RR.Iron porphyrin homogeneous catalysts have been widely concerned because of their high efficiency and stability,and their structures are easy to be modified,which can regulate the activity of electrocatalysis.As we all know,the type of solvent and the structure of catalyst will directly affect the catalytic performance of catalyst.In order to solve these problem,In this thesis,effects of CO2 RR and the influence of porphyrin ligand structure on CO2 RR were studied.The main contents of this paper are as follows:Firstly,we studied FeⅢ chloride tetrakis(pentafluorophenyl)porphyrin(1)as a catalyst for CO2 reduction in different solvents.Fe porphyrin 1 is known to have poor electrocatalytic activity for the CO2-to-CO conversion in dimethylformamide.In this work,we re-examined Fe porphyrin 1 as a CO2 reduction catalyst in various solvents.Our results show that 1 displays fairly high electrocatalytic CO2-to-CO activity in acetonitrile with a turnover frequency(TOF)up to 4.2 × 104 s-1.On the other hand,1 shows a modest activity in propylene carbonate,and is inefficient to catalyze CO2 reduction in benzonitrile,dimethylformamide,and tetrahydrofuran.Several solvent effects were considered,but none of these effects alone can explain the observed large activity difference of 1 for CO2 reduction in these solvents.Based on the results,it is suggested that more care should be paid when comparing different CO2 reduction catalysts because solvent effects are significant and are underevaluated.Secondly,a Fe porphyrin with an inverse axial ligand was designed for CO2 reduction.The tail group of the inverse axis of the catalyst is imidazole,which can regulate the electronic structure of the central metal of the catalyst.Thus,the catalytic performance of Fe porphyrin for CO2 reduction can be regulated.The properties of the catalysts were studied by means of NMR,MS,electrochemistry and so on.The results show that the catalysts has stable catalytic performance for CO2 reduction,which provides a precondition for exploring the regulation of the electronic structure of the central metal by the axial ligands.