Excessive emissions of carbon dioxide(CO2)in the atmosphere result in a series of energy and environmental issues all around the word.Thus,it is urgent to prepare efficient materials for the conversion of CO2 as a C1 source into energy-related chemical products.Porous metal–organic frameworks(MOFs)are a class of rapidly growing crystalline materials,which have attracted significant attention for application in the conversion of CO2 into cyclic carbonates.Therefore,the research work in this thesis focuses on the development of high-efficiency MOFs-based catalysts for the formation of cyclic carbonates from carbon dioxide and epoxides.The first MOFs-based catalyst:using the designed and synthesized 2,6-bis(2,4-dicarboxylphenyl)-4-(4-carboxylphenyl)pyridine(H5BDCP)as organic ligand,one highly robust microporous framework of{(Me2NH2)[Tm3(BDCP)2)(H2O)3]?4DMF?H2O}n(NUC-25)was synthesized by skillfully integrating the wave-like 2D sheet of[Tm(CO2)3(H2O)]n and mononuclear unit of[Tm(CO2)4(H2O)2],which contains near-rectangular nanochannels.Furthermore,the activated NUC-25 with the removal of associated water molecules is a rarely reported bifunctional heterogeneous catalyst.Just as expected,NUC-25 exhibits greatly high catalytic activity for the cycloaddition reaction of epoxides with CO2 into alkyl cyclic carbonates under bland solvent-free conditions,which should be ascribed to the devotion of nitrogen-containing pyridine heterocycles as Lewis base sites on the inner surface of nano-caged voids and the recognized Lewis acid sites of Tm3+cations.The experimental results strongly prove that the pre design of multi carboxyl nitrogen-containing heterocyclic ligands for the assembly of MOF catalyst is an ideal strategy to improve the performance of CO2cycloaddition reaction.The second MOFs-based catalyst:by integrating the coplanar[Tm4(CO2)10(μ3-OH)2(μ2-HCO2)(H2O)2]clusters and structure-oriented functional BDCP5-ligand,leading to one highly robust nanoporous tetranuclear{Tm4}-organic framework,{(Me2NH2)[Yb4(BDCP)2(μ3-OH)2(μ2-HCO2)(H2O)2]?7DMF?5H2O}n(NUC-37).NUC-37possesses hierarchical microporous and nanoporous channels with larger pore size and specific surface area than NUC-25.The inner wall of NUC-37 is characterized by plentiful coexisted Lewis acid-base sites,including open Tm3+sites,Npyridineatoms,μ3-OH andμ2-HCO2 ions.The catalytic experimental studies exhibit that NUC-37 possesses high selective catalytic activity on the cycloaddition of epoxides with CO2 as well as high recyclability under mild conditions,which should be ascribed to its nanoscale channels,rich bifunctional active sites,large surface areas,and stable physicochemical properties.This work offers an effective means of synthesizing the productive cluster-based Ln-MOF catalysts by employing structure-oriented ligands and controlling the solvothermal reaction conditions. |