Effect Of Acid And Base On Photocatalytic And Electrocatalytic Carbon Dioxide Reduction By Cobalt And Rhenium Metal Complexes

With the increase of human’s demand for energy,it leads to the excessive use of fossil fuels,causing the increasingly serious greenhouse effect and other problems.Making full use of solar energy and electricity from solar energy to drive molecular catalysts to reduce carbon dioxide（CO₂）into fuel or high value-added chemicals is particularly important,which is one of the ideal ways to mitigate climate warming and energy problems.Recently,many transition metal molecular catalysts have been developed,but many of them have low catalytic efficiency.Therefore,it is very important to design and synthesize efficient molecular catalysts and improve the catalytic efficiency by optimizing the reaction conditions.The addition of Lewis acid or base can improve the catalytic activity significantly.Based on the above problems,this paper uses oxanthracene bridged tetrapyridine and bipyridine as ligands to synthesize metal cobalt and rhenium complexes as carbon dioxide reduction catalysts,by adding Lewis acid or base to improve the efficiency of electron transfer,thus enhancing the performance of the catalyst.The effects of different Lewis acids and bases on the photocatalytic and electrocatalytic efficiency of cobalt and rhenium complexes were investigated.The details are as follows:1.A cheap metal-cobalt complex biqpy Co（Cl O₄）₂（biqpy=4,4’’’’-（2,7-di-tert-butyl-9,9-dimethyl-9H-xanthene-4,5-diyl）di-2,2’:6’,2’’:6’’,2’’’-quaterpyridine）was designed and synthesized.Using above-mentioned complex as molecular catalyst,organic small molecule2,4,5,6-tetra（9H-carbazol-9-yl）isophthalonitrile（4Cz IPN）as photosensitizer,triethylamine（TEA）and 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole（BIH）as sacrificial agent,a photocatalytic CO₂ reduction system for non-precious metal molecules was established.biqpy Co（Cl O₄）₂ showed excellent activity of photocatalytic reduction of CO₂.The reduction product was HCOO^-,which was rarely reported.The turnover number was 376,the selectivity was 97%,and the yield of HCOO^-was 37.59μmol,which is higher than other two cobalt-based catalysts of biqpy Co₂Cl₄ and qpy Co（Cl O₄）₂·2H₂O.In addition,biqpy Co（Cl O₄）₂showed good electrocatalytic activity when TEA was added in the electrocatalytic system,which corresponded to the good photocatalytic activity of biqpy Co（Cl O₄）₂ in the presence of TEA.2.In order to further improve the catalytic performance of oxanthracene bridging complexes,the metal-rhenium complex 4-bibpy Re（CO）₃Cl（bibpy=4,4’’-（2,7-di-tert-butyl-9,9-dimethyl-9H-xanthene-4,5-diyl）di-2,2’-bipyridine）was designed and synthesized by changing the ligand qpy and metal center Co on the basis of the previous chapter.A photocatalytic system was established using Ru（bpy）₃Cl₂·6H₂O（bpy=2,2’-bipyridine）as the photosensitizer,BIH as the sacrificial agent and Br?nsted acid phenol（Ph OH）as the proton source.4-bibpy Re（CO）₃Cl showed excellent activity of photocatalytic reduction of CO₂.The reduction product was CO.The turnover number was up to 1168 and the selectivity was 100%.When Ph OH is added to the electrocatalytic system,4-bibpy Re（CO）₃Cl shows good electrocatalytic activity,which is in accordance with the good photocatalytic activity of 4-bibpy Re（CO）₃Cl in the presence of Ph OH.In addition,the addition of TEOA or Lewis acid metal ion of Ni²⁺or Ca²⁺promoted the photocatalytic efficiency.