Preparation And Catalytic Performances Of Nanomaterials Derived From Metal-Organic Frameworks

The contradiction between supply and demand of fossil fuels and the problem of environmental pollution are becoming increasingly serious.Thus,it is urgent to develop clean and renewable energy sources.Hydrogen energy and ammonia fuel are two clean and efficient energy sources,and the search for suitable catalysts to obtain high-performance hydrogen storage materials and produce ammonia have important research significance.Metal organic framework(MOF)and covalent organic framework(COF)are two types of emerging porous crystalline materials,which can be used as precursors to prepare nanomaterials with various morphologies and structures.And the unique structure properties can provide suitable pores and high active sites,which are beneficial to achieve rapid mass transfer and improve the catalytic performance during the catalysis process.Therefore,in this thesis,MOF and COF are used as precursors to prepare a variety of new catalysts,which can be used to catalyze hydrogen production and produce ammonia by fixing nitrogen.The main research contents of the thesis are as follows:(1)Ni-MOF was synthesized by a hydrothermal method using terephthalic acid and nickel chloride as the organic ligand and metal salt,respectively.Then Ni/C was obtained with a heat treatment process in argon atmosphere.The as-synthesized Ni/C retained the frame structure of MOF and contained graphitized and defective carbon materials.In the NRR reaction,the Ni/C electrocatalyst achieved the highest ammonia production rate(66.57 mg h^-1 mg^-1_cat)and Faraday efficiency(33.67%)at-0.9 V in 0.1 M KOH electrolyte.(2)Rod-like COF material was synthesized by a hydrothermal method,which was used as a catalyst to improve the hydrogen storage performance of LiBH₄.Thermal dehydrogenation of LiBH₄ is found to startat ca.93.67?.(3)A two-step annealing method was used to convert the as-prepared Ni/COF into Ni/NiO/C catalytic material,which was used as an electrocatalyst for the NRR reaction,and its nitrogen reduction performance was studied in detail.After Ni/NiO/C was utilized to catalyze nitrogen in 0.1 M KOH electrolyte,the ammonia yield was 70.75 mg h^-1mg^-1_cat,and the Faraday efficiency can reach 39.76%.(4)Co/Ni-MOF was prepared with a simple solvothermal method,which was used as a precursor to mix with thiourea.Then,the Co Ni₂S₄/C nanomaterial was synthesized through a high-temperature carbonization process and used as an electrocatalyst for the NRR reaction.In 0.1 M KOH electrolyte solution,the Co Ni₂S₄/C electrocatalyst brought the highest ammonia yield rate(223.95 mg h^-1 mg^-1_cat)at-1.7 V and Faraday efficiency(16.05%)at-1.4 V.