Construction Of Nickel Catalysts Supported On Schiff-base Covalent Organic Frameworks And Its Catalytic Performance For Ethylene Oligomerization

Covalent organic frameworks（COFs）,as a new type of crystalline organic porous materials,have the advantages of high specific surface area,low density,high crystallinity and adjustable building units.COFs are widely used in gas storage,energy storage,photocatalysis,heterogeneous catalysis,sensing,photoelectricity and other fields,which have become one of the research hotspots in materials in recent years.In this thesis,based on the systematic and comprehensive review of homogeneous and heterogeneous catalysts for ethylene oligomerization and COFs materials,one-dimensional Schiff-base polynuclear nickel catalyst,two-dimensional Schiff-base COFs supported nickel catalysts and three-dimensional Schiff-base COFs supported nickel catalyst were synthesized by using three kinds of amino compounds as main building units and butanedione and terephthalaldehyde as auxiliary building units,and their catalytic performance for ethylene oligomerization was systematically investigated.The main research contents and results are as follows:1.One-dimensional Schiff-base ligand（PS-ligand）and its corresponding one-dimensional Schiff-base polynuclear nickel catalyst（PS-Ni complex）were synthesized by polycondensation and coordination reaction with p-phenylenediamine and 2,3-butanedione as raw materials,（DME）Ni Cl₂ as metal precursor and organic acid as catalyst.IR,SEM,NMR and other characterization methods confirmed that the chemical structure of PS-ligand and PS-Ni complex were consistent with the theoretical structure.With MAO as cocatalyst and cyclohexane as solvent,PS-Ni complex had a good catalytic performance for ethylene oligomerization.When the reaction pressure was 0.5 MPa,the reaction temperature was 25℃,the molar ratio of Al/Ni was 500 and the reaction time was 60 min,the highest catalytic activity of PS-Ni complex for ethylene oligomerization was 17.62×10⁵ g/（mol Ni·h）and the selectivity of C₄ and C₆ olefins was highest.2.Two-dimensional Schiff-base covalent organic frameworks（MABD-COF and MAPA-COF）and their corresponding two-dimensional Schiff-base covalent organic framework supported nickel catalysts（Ni@MABD-COF and Ni@MAPA-COF）were synthesized by polycondensation and coordination reaction with melamine,2,3-butanedione and terephthalaldehyde as raw materials,（DME）Ni Cl₂ as metal precursor and organic acid as catalyst.IR,SEM,NMR,and other characterization methods confirmed that the chemical structures of the synthesized MABD-COF,MAPA-COF,Ni@MABD-COF and Ni@MAPA-COF were consistent with the theoretical structure.3.With MAO as cocatalyst and cyclohexane as solvent,Ni@MABD-COF and Ni@MAPA-COF had good catalytic performance for ethylene oligomerization.When the reaction pressure was 0.5 MPa,the reaction temperature was 25℃,the reaction time was 60min,and the molar ratio of Al/Ni was 700 and 500,respectively,the highest catalytic activity of Ni@MABD-COF and Ni@MAPA-COF for ethylene oligomerization was 7.62×10⁴ g/（mol Ni·h）and 12.86×10⁴ g/（mol Ni·h）,respectively,and the main products of C₄ and C₆ were up to 90%.After three cycles,the catalytic activity of Ni@MABD-COF and Ni@MAPA-COF decreased slightly and the distribution of oligomerization products was almost not affected by the number of cycles,which proved that Ni@MABD-COF and Ni@MAPA-COF had excellent regeneration properties.4.Three-dimensional Schiff-base covalent organic framework（TAPA-COF）and its corresponding three-dimensional Schiff-base covalent organic framework supported nickel catalyst（Ni@TAPA-COF）were explored by polycondensation and coordination reaction with tris（4-aminophenyl）amine and terephthalaldehyde as raw materials,（DME）Ni Cl₂ as metal precursor and organic acid as catalyst.IR,SEM,NMR,and other characterization methods confirmed that the chemical structures of the synthesized TAPA-COF and Ni@TAPA-COF were consistent with the theoretical structure.With MAO as cocatalyst and cyclohexane as solvent,Ni@TAPA-COF had good catalytic performance for ethylene oligomerization.When the dosage of precatalyst was 2μmol,the Al/Ni molar ratio was 500,the ethylene pressure was 0.5 MPa,the reaction time was 60 min and the reaction temperature was 25℃,the highest catalytic activity of Ni@TAPA-COF for ethylene oligomerization was 15.18×10⁴g/（mol Ni·h）and the content of C₆ was up to 57.71%.Ni@TAPA-COF also had excellent catalytic stability and extraordinary regeneration performance.5.The effect of ligand structure on the catalytic performance of three kinds of organic polymer supported nickel catalysts for ethylene oligomerization showed that the products of three kinds of catalysts are mainly C₄-C₆ olefins,and the catalytic activity sequence for all catalysts was as follows:PS-Ni complex>Ni@TAPA-COF>Ni@MAPA-COF>Ni@MABD-COF.