Synthesis Of 3D Graphene Supported Nickel- Cobalt Catalysts For Electrocatalytic Reduction Of Linfen Lignite

A three-dimensional graphene-supported nickel-cobalt bimetallic electrocatalyst（3D Ni-Co/G）was prepared with combining hydrothermal reduction and freeze-drying techniques,the graphene composite materials loaded with different metals were used as working electrodes.Cyclic voltammetry and current-time curve methods were applied to systematically study the catalytic activity and stability of the catalyst on the electrochemical reduction of coal-based model compounds and Shanxi Linfen lignite（LL）in an H-type membrane electrolytic cell equipped with three-electrode.The main results are as follows:（1）X-ray diffraction,scanning electron microscopy（SEM）and high-resolution transmission electron microscopy combined energy spectrum analysis and other methods were employed to characterize the synthesized catalyst.Results show that the prepared catalyst is a graphene-supported nickel-cobalt bimetal composite materials with high specific surface area（498.11 m²/g）and rich mesoporous structure.Besides,a series of Ni-Co bimetallic catalysts with different particle sizes（about 11 nm）can be prepared by adjusting the ratio of nickel/cobalt precursors and controlling the calcination temperature.（2）The 3D Ni-Co/G catalyst was prepared into the corresponding solution and coated on the surface of the glassy carbon electrode（GCE）as the working electrode,the cyclic voltammetry behavior of model compounds 1-acetylnaphthalene,dibenzyl ether and anthracene on GCE were investigated over 3D Ni-Co/G with DMF as the solvent,EtOH as the hydrogen source,and Bu₄NBr as the supporting electrolyte.Electrolysis products were qualitatively analyzed with orbitrap mass spectrometry and gas chromatography-mass spectrometry（GC-MS）to evaluate hydrogenation performance of the catalyst.Simultaneously,the effects of catalyst composition,solvent ratio,electrolysis potential,and electrolysis temperature on the reaction were discussed.Results prove that the electrocatalytic hydrogenation of coal-based model compounds over 3D Ni-Co/G catalyst is feasible,and the reactants will generate corresponding hydrogenation products after electrocatalysis.（3）Eight kinds of imidazole ionic liquids（IL）were prepared by microwave method and characterized by Fourier infrared spectroscopy（FTIR）and ¹H NMR.Under normal temperature and pressure,the swelling performance of IL to LL was investigated based on the swelling degree and the structural change of coal.Results show that[Bmim]Br is a better solvent for LL swelling and dissolving.FTIR and SEM showed that the molecular structure of LL changed after swelling by IL,which was conducive to the electrolytic reaction.（4）The prepared 3D Ni-Co/G was pressed on nickel foam as the working electrode to study the LL electro-catalytic reduction after the swelling pretreatment by IL with NaOH as the solvent,H₂O as the hydrogen source and Bu₄NBr as the supporting electrolyte.After the electrolysis,the solid/liquid products are separated and further purified.The composition of the liquid products was analyzed by GC-MS,the solid products were characterized with FTIR,¹³C NMR and elemental analysis for deep insights into the compositional changes of functional groups and elements in coal before and after electrolysis.Results show that the 3D Ni-Co/G has great hydrocracking effect for the LL electrolytic reduction.Compared with raw LL,the relative contents of phenol,alkanes,alcohols and naphthenes compounds in electrolysis coal greatly improved,and the catalyst has optimal catalytic performance for LL electroreduction when the ratio of nickel and cobalt is 1:1.There are 70 figures,10 tables,and 118 references in this thesis.