Hydrogenation And Upgrading Of Lignin-Derived Phenolic Compounds Under The Action Of Metal-Supported Catalysts

Compared with fossil energy,biomass resources have the advantages of wide sources,green and renewable,and the utilization of biomass will not cause problems such as environmental pollution and greenhouse effect.Liquid bio-oil can be obtained from solid biomass by pyrolysis or liquefaction,but untreated bio-oil contains a large amount of oxygenates（mainly phenolic compounds）from lignin degradation,resulting in bio-oil components.Complex,poor stability,high oxygen content,and low effective hydrogen-carbon ratio,it is not suitable for direct use as high-quality liquid fuel,and requires further refining and upgrading.Bio-oil upgrading and refining methods commonly used in research at home and abroad mainly include catalytic reforming,catalytic cracking,and catalytic hydrogenation,all of which require the use of metal-rich hydrogenation catalysts.Bifunctional catalysts prepared by metal-supported oxides are often used in the catalytic hydrogenation process of bio-oil,and have the advantages of high catalytic efficiency and recyclability.In this study,three types of catalysts Ni or/and Mn supported on CeZrO₂,Ni or/and Mn supported on Nb₂O₅ and Ru/CeO₂ catalysts were prepared by incipient wetness impregnation method,and phenol and guaiacol were selected as bio-oil model compounds.Hydro-upgrading process of bio-oil model compounds supported by different metal-like oxide catalysts.（1）First,Ni or Mn were loaded on CeZrO₂,and Ni/CeZrO₂,Mn/CeZrO₂ and Ni-Mn/CeZrO₂ catalysts were prepared by incipient wetness impregnation method.The hydrodeoxygenation of guaiacol,a model compound of bio-oil,was studied.By means of characterization,it is found that the active metal sites on the catalyst have high dispersion,which can improve the catalytic activity of the catalyst in the hydrogenation process of phenolic compounds.The reaction performance of the catalysts was measured,and the bimetallic catalysts showed better hydrogenation activity,and guaiacol（200℃,1 MPa N₂）could be effectively converted into cyclohexanol with a yield of 73.3%.The hydrogenation method used here is in-situ hydrogenation,and hydrogen production through the reforming reaction of isopropanol and water provides a hydrogen source for the reaction.Compared with traditional hydrogen hydrogenation,it is safer and worthy of further study.（2）On the basis of the previous research,this work adopts the impregnation method to synthesize a bimetallic catalyst supported on a Nb2O5 hydrogenation catalyst,and uses a low-carbon alcohol as a hydrogen-donating solvent to perform in-situ hydrogenation of guaiacol.Hydrogen donating capacity of hydrogen solvent.On different bimetallic catalysts,guaiacol can be efficiently converted to cyclohexanol.By means of BET,NH₃-TPD,XRD,XPS,SEM and TEM,the structure and characteristics of Ni-Mn/Nb₂O₅ catalyst with better catalytic performance were determined.Compared with the catalyst,Ni-Mn/Nb₂O₅ has the characteristics of high metal dispersion and large pore size,which may be helpful for the in-situ hydrogen production of hydrogen-donating solvents and the hydrogenation of phenolic compounds.The reaction performance of the catalyst was carried out.It was found that using isopropanol as the hydrogen donor,the reaction temperature was 200℃ and the reaction time was 5 h,the guaiacol could be completely converted,and the yield of cyclohexanol was 71.8%.At the same time,the effects of different hydrogen donors such as isopropanol,sec-amyl alcohol and ethylene glycol on the in-situ hydrogenation of guaiacol were studied in detail.The donor showed good in-situ hydrogen production,so isopropanol was the best hydrogen-donating solvent.（3）Due to the harsh conditions of deoxygenation（high temperature or sufficient acidity）,on the basis of previous research,the preparation of metal-supported catalysts with stronger hydrogenation ability and catalytic activity was considered to further optimize the hydrogenation and upgrading process of phenols,and then The purpose of high-efficiency improvement of bio-oil model compounds.Therefore,Nb₂O₅,CeO₂,ZrO₂,Al₂O₃ supported Ru-based catalysts were prepared by incipient wetness impregnation,and the hydrodeoxygenation of phenol was studied.The results show that the Ru/CeO₂catalyst prepared with CeO₂ generated by the pyrolysis of cerium carbonate as a carrier exhibits excellent catalytic activity,and phenol can be efficiently converted into cyclohexanol under mild conditions（140℃,3 MPa N₂）,and the target product cyclohexane The alcohol yield is as high as 95.6%,indicating that the catalyst has remarkable hydrogenation and deoxygenation performance.Through characterization,it is found that Ru metal active sites have the advantages of small particle size and high dispersibility on the catalyst,and there are certain oxygen vacancies on the catalyst support,which may be one of the reasons for the high activity of the catalyst.