Study On Catalytic Cleavage The C-O Bond Of Lignite Model Compounds Over Nickel-based Catalysts

Lignite organic matter is rich in aryl ether bridges.Selective cleavage of the aryl ether bridges of lignite organic macromolecules by catalytic hydrogenation is not only beneficial to understand the macromolecular structure of lignite,but also to achieve the directional depolymerization and high value-added utilization of lignite.In this thesis,catalytic hydrogenolysis?CH?of lignite model compounds was studied.The properties of Ni/AC and Ni-Ru/AC catalysts and reaction mechanism of CH process were investigated.In addition,CH and non-catalytic hydrogenolysis?NCH?of lignin and ShengLi lignite?SL?were carried out and the organic compounds of products were analyzed by gas chromatography/mass spectrometry?GC/MS?.Nickel-based catalysts?Ni/AC,Ni/HZSM-5 and Ni/?-Al₂O₃?were prepared by impregnation method,and the catalytic activity of the catalyst was tested by using the benzyl phenyl ether?BPE?as lignite model compound.The kinetic studies indicated that the order of initial turnover frequency?TOF?of BPE over three Ni-based catalysts was Ni/AC(64 mol/mol Ni_surf?h)>Ni/?-Al₂O₃(58 mol/mol Ni_surf?h)>Ni/HZSM-5(45 mol/mol Ni_surf?h).The order of apparent activation energy?E_a?was Ni/AC?41 kJ/mol?<Ni/?-Al₂O₃?56 kJ/mol?<Ni/HZSM-5?60 kJ/mol?.These results all proved that the type of supports significantly affected CH activity of BPE and Ni/AC was the highest activity catalyst in CH of the C-O bond of BPE.Toluene and phenol were major products in CH of BPE.The reaction mechanism of cleaving C-O bond of BPE over Ni/AC was also proposed.In order to improve the activity and stability of the Ni/AC under mild conditions,a bimetallic catalyst Ni-Ru/AC was prepared by doping the noble metal Ru in the Ni/AC.The catalysts were characterized by various characterization methods such as XRD,XPS,TEM-EDS,SEM-EDX and BET.The characterization results proved that a“synergistic effect”was formed between Ni and Ru.This“synergistic effect”could result in the generation of additional surface active sites,small size of metal particles and high dispersion of metal particles.Thereby improved the overall reactants conversion and modified the product distribution.The bimetallic Ni-Ru/AC exhibits lower reaction E_a?18.3 kJ/mol?and higher TOF(62.7 h^-1)than monometallic Ni/AC.The reaction mechanism of cleaving C-O bond of BPE over Ni-Ru/AC was also proposed.The CH experiments lignin and SL were performed over bimetallic Ni-Ru/AC.The product components were analyzed by GC/MS with NCH as a comparison.The yields of the soluble component from CH of lignin was higher than the yields of NCH,which not only effectively cleave the C-O bond of the lignin macromolecular structure to form an aromatic monomer,but also remove the hydroxyl group of the phenolic compound.Additionally,the soluble components from CH and NCH of SL mainly consist of phenols,arenes,alkanes,alkenes,ketones,lipids and other organic compounds.The yields of phenols of CH were much higher than the yields of NCH.The results also indicated that the Ni-Ru/AC could efficiently crack the C-O bonds in the macromolecular structure of the coal to form aromatic compounds.