Synthesis Of Reductive POMs-based Coordination Compounds For Photo-and Electrocatalytic CO₂ Reduction

Photo-/Electrocatalytic CO2 reduction reaction can selectively reduce excess CO2 in the air into available Ci?Cn products,which is of great significance for sustainable development of human beings.POMs-based heterogeneous molecular catalysts with the well-defined structure,excellent redox activity and thermal stability have shown good application prospects in the field of CO2 reduction.Traditional POMs are difficult to be separated from catalytic systems because of their easy solubility,which is not conducive them to be further researched.Therefore,the design and synthesis of recycled POMs-based heterogeneous crystalline catalysts with high activity,selectivity and stability have become the persistent goal of the Chemists.In this thesis,we chose {P4MoV6O3iH6}6-(abbr.{P4MoV6})unit with strong reducibility as the research object,which connected with transition metal ions or nitrogenous organic ligands through coordination bond or weak interaction into the reaction system to construct several novel POMs-based heterogeneous catalysts.Then,we researched the activity of these compounds in the field of photo/electrocatalytic CO2 reduction.Two inorganic POMs-based crystalline materials(NENU-605 and NENU-606)with strong reducibility were synthesized by hydrothermal synthesis method under the control of reaction conditions(temperature,pH,etc.)and used as heterogeneous catalysts for photocatalytic CO2 reduction reaction,realizing the highly selective reduction of CO2 to CH4 in aqueous solution.Photocatalytic analysis revealed that the hetero-metallic active sites of NENU-606 finally exhibited a higher CH4 generation selectivity(85.5%)in the photocatalytic CO2RR than those of NENU-605(76.6%).To our knowledge,this is the first report of {P4MoV6}-based crystalline inorganic materials applied in the photocatalytic CO2RR.Ultimately,this work was published on Chen.Sci.,2019,10,185-190 and highlighted by X-MOL.By analyzing the structure of single crystal,element composition and TG,the chemical formulas are determined as follows:NENU-605:H{[Na2K4Mn4(PO4)(H2O)4](?){[MO6O12(OH)3(HPO4)3(PO4)]4[Mn6(H2O)4]}·16H2ONENU-606:H{[Na6CoMn3(PO4)(H2O)4][{[MO6O12(OH)3(HPO4)3(PO4)]4[Co1.5Mn4.5]}·21H2O Adopting the hydrothermal synthesis method and controlling the reaction temperature at 180?,adjusting the pH of the solution about 3,we successfully obtained three new organic-inorganic hybrid POMs-based crystalline materials,which are mainly made of {P4MoV6} unit with strong reducibility,nitrogenous organic ligand(4,4'-Vinylenedipyridine)and transition metal ions(Co? or Fe?).Then,they were used as heterogeneous catalysts in the field of electrocatalytic reduction CO2 to achieve the efficient conversion of CO2 to HCOOH.Electrocatalytic analysis revealed that the efficiency of NENU-609 with the highest degree of unsaturated coordination at the metal active site is optimal.When the applied voltage is-0.7V vs.RHE,the faraday efficiency of HOOH reaches 52.3%.Moreover,the types of metal active sites also have an impact on the electrocatalytic reduction performance of CO2:NENU-608(Co?,-0.6v,FEHCOOH=21.3%),>NENU-610(Fe?,-0.6v,FEHCOOH=11.2%).By analyzing the structure of single crystal,element composition and TG,the chemical formulas are determined as follows:NENU-608:2(C12H12N2)[Mo6O12(OH)3(HPO4)3(PO4)]2[Co3(C12H11N2)2(H2O)2]·8H2ONENU-6092(C12H12N2)2(Cl2H11N2)[Mo6O12(OH)3(HPO4)3(PO4)]2[Co3(H2O)6]·10H2ONENU-610:2(C12H11N2)3(C12H12N2)[Mo6O12(OH)3(HPO4)3(PO4)]2[Fe2(H2O)2]· 6H2O...