Synthesis And Catalytic Properties Of Advanced Porous Materials For Carbon Dioxide Capture And Conversion

As the improving of human beings’ living standards and the increasing of industrial activities,the concentration of atmosphere carbon dioxide(CO2)is increasing constantly.As a major component of greenhouse gases(GHGs),excessive CO2 emissions have led to a variety of environmental issues.Hence,CO2 capture and conversion have aroused widespread attention in the academic community in recent years.However,conventional adsorbents and catalysts still have many drawbacks with respect to CO2 capture and conversion.In the past two decades,advanced porous materials such as porous polymers(POPs)and metal-organic framework(MOFs)exhibit excellent performances and application prospects in CO2 capture and conversion due to the designable and tailorable structure,adjustable pore size and relatively high specific surface area.In this thesis,we have synthesized several different kinds of advanced porous materials with high stability based on cheap raw materials.In addition,upon pyrolysis,material compositization,and other post-synthetic modification,the pore sizes of these materials can be adjusted with the introduction of novel catalytic active sites,thus improving their performances in CO2 capture and conversion.The main research results are as follows:1.In view of the small pore size and poor stability of traditional CO2 adsorbents and catalysts,a hierarchically porous phenolic resin-type polymer(PRP-1)was prepared by a one-step solvothermal synthesis from two cheap polymer monomers(phloroglucinol and 4,4’-biphenyldicarboxaldehyde).Due to the relatively high stability and specific surface area,hierarchical pores as well as high-density phenolic hydroxyl group,PRP-1 not only exhibited outstanding CO2 capture capacitiy but also showed high activity for catalyzing the CO2 fixation reaction.At 298 K and 1 bar,the CO2 uptake capacity of PRP-1 can reach up to 71 mg g-1.Besides,there was no apparent drop in the CO2 adsorption capacity during 10 cycles of CO2 uptake.In addition,with the aid of tetrabutyl ammonium bromide,PRP-1 can catalyze the conversion of CO2 cycloaddition with diverse epoxides under mild conditions with no remarkable drop during 6 runs of cycling,indicating its good catalytic stability.2.The types and quantities of active sites play a critical role in catalysis.However,traditional catalysts generally have single structures,and it is difficult to introduce multiple catalytic sites,especially the acidic and basic sites simultaneously into a single catalyst.As a kind of relatively novel crystalline porous materials,MOFs can introduce multiple catalytically active sites in a single catalyst by selecting different metal centers and organic linkers.Besides,the MOF derivatives afforded by thermal conversion of MOFs can not only inherit the structural advantages of the original MOF but also present new properties.As for this,the ZIF-8 template was pyrolyzed to give ZnO@NPC composite with high specific surface area.Upon the subsequent oxidization by sodium hypochlorite,hydroxyl and carboxyl groups can be introduced into framework while retaining original catalytic active sites(zinc oxide and pyridinium nitrogen).Based on the synergy between multiple catalytic active sites and the porosity inherited from ZIF-8,the oxidized catalyst(ZnO@NPC-Ox)displayed remarkable catalytic activity,selectivity and stability for CO2 cycloaddition of epoxy compounds under mild conditions.3.The rational integration of multiple functional components into a composite material could result in enhanced activity tailored for specific applications.The modifiable pore cavities of MOFs provide favorable conditions for material recombination.In this context,an ethanol solution of ionic liquid(imidazolium salt),1,2-divinylbenzene and isobutyronitrile(AIBN)was introduced into the pores of MIL-101 via incipient-wetness impregnation method.The poly(ionic liquid)s was obtained from the radical copolymerization reaction initiated by AIBN at 70℃ and then confined within the pores of MIL-101,which further enhancing the CO2 adsorption performance of the resultant composites(polyILs@MIL-101).On the basis of the the good CO2 enrichment capacity as well as the synergistic effect between Lewis base sites in the ionic liquid and the Lewis acid sites in MIL-101,polyILs@MIL-101 represented significantly enhanced activity for the catalysis of the cycloaddition of CO2 with epoxides,surpassing both of the polylLs and MIL-101.Remarkably,the catalytic activity of polyILs@MIL-101 is well retained during the 10 runs of cycling reaction.Additionally,when subatmospheric pressure CO2 was utilized as C1 resource,unlike the sharply reduced activity of ionic liquid,polyILs@MIL-101,as a heterogeneous catalyst with CO2 enrichment ability,can maintain its catalytic activity,proving that the importance of CO2 adsorption capacity of catalysts to in their catalytic performance for CO2 conversion.