Preparation,Characterization And Catalytic Performance Of Polyoxometalate Functionalized Nitrogen-Rich Covalent Organic Framework Materials

Covalent organic framework materials(COFs)are a new type of porous material composed of C,H,O,N,and B elements.The framework contains a wealth of preset functional group sites,with a large specific surface area and the characteristics of adjusted pore volume and aperture make it widely used in gas storage,catalysis,adsorption and semiconductor fields.Among them,nitrogen-rich COFs coordinate with the nitrogen atoms and other functional groups in the material,and some active sites(such as transition metal ions,metal complexes and heteropoly acids,etc.)can form an interaction and be effectively immobilized on nitrogen-rich COFs.Above,inhibiting the aggregation of active sites is an important type of catalyst carrier.Polyoxometalates(POMs),as a cheap and efficient acidic oxidizing material,are excellent catalytically active substances.However,because POMs are easily soluble in water and most organic solvents,they are usually homogeneous in catalytic reactions.It is difficult to separate,which is not conducive to recycling and reuse,which may cause pollution and increase production costs.Therefore,the preparation of supported polyoxometalate catalysts has become a research focus.In this work,the two types of polyoxometalate(PCuMo₁₁)catalysts prepared are used in epoxidation of styrene and hydrogenation of nitrobenzene.The main research contents are as follows:(1)Nitrogen-rich COFs(SNW-1,PC and CIN-1)were prepared by solvothermal method,and supported composite materials(PCuMo₁₁@SNW-1,PCuMo₁₁@PC and PCuMo₁₁@CIN-1)were prepared by impregnation method,the characterization results show that PCuMo₁₁ has been uniformly dispersed on the surface or inside of nitrogen-rich COFs,and a relatively stable chemical connection has been established between the two.Applying the prepared composite material to the air styrene epoxidation reaction,the conversion of styrene can reach 93%?98%,and the selectivity of styrene oxide is 76%?84%,respectively.(2)Research on the catalytic hydrogenation of nitrobenzene has been carried out.High temperature carbonization of nitrogen-rich COFs(CIN-1 and PC)to obtain nitrogen doped carbon materials(CC-700 and NC-700),and immobilized them on PCuMo₁₁ to obtain multiphase composite materials(PCuMo₁₁@CC-700 and PCuMo₁₁@NC-700),to catalyze the hydrogenation of nitrobenzene with hydrazine hydrate as the hydrogen source.Taking CC-700 as an example to catalyze the hydrogenation of nitrobenzene,graphite nitrogen and its defects are discussed as the active sites of the reaction.When PCuMo₁₁@NC-700 is used as a catalyst,the reaction time is shortened to 45 min,the conversion of nitrobenzene is 91%,and the selectivity of aniline is higher than 99%,which speeds up the reaction and improves the catalytic efficiency.In summary,the research in this paper helps expand the application range of polyoxometalates and covalent organic framework materials in the field of catalysis.