Preparation Of Iron/Nitrogen Co-doped Carbon Supported Ni Catalyst And Its Catalytic Hydrogenolysis Of Lignin

Lignin is an important renewable energy for the producation of high value-added chemicals,which is a three-dimensional polymer of different phenylpropane units connected by the random combination of different C-O and C-C bonds.The utilization of lignin to produce high value-added chemicals is conducive to alleviating the fossil energy crisis.In this thesis,Ni nanoparticles supported on iron/nitrogen co-doped carbon was prepared by co-pyrolysis and solvothermal reduction method.The catalysts were prepared under different contiditons including different iron precursor,calcination temperature,N/C ratio,Ni precursor and Ni loading,and the optimal catalyst that is Ni_10%@Fe/NC_0.33-800（iron precursor:Fe（NO₃）₃,calcination temperature:800℃,N/C ratio:0.33,Ni precursor:Ni（AC）₂,Ni loading:10%）was used to catalytic hydrogenolysis（CH）of lignin model compound.Combined with the catalyst characterization and detailed product analysis,and the reaction pathway of CH process were proposed.CH of dealkalized lignin（AL）,alkali lignin（AL）,and kraft lignin（KL）over Ni_10%@Fe/NC_0.33-800 were futher conducted and the compositions of resulting obtained product were analyzed.Ni_10%@Fe/NC_0.33-800 showed good catalytic performance on the selective cleavage of C-O bond of benzyl phenyl ether（BPE）and phenoxy ethylbenzene（PPE）.The BPE conversion reached up to 97.7%over Ni_10%@Fe/NC_0.33-800 under mild conditions（230℃,1 MPa H₂,and 0.5 h）with toluene and cyclohexanol as the major products.PPE was primarily converted into cyclohexane and ethylbenzene over Ni_10%@Fe/NC_0.33-800 under 270℃,1 MPa H₂,and 4 h.High-resolution transmission electron microscopy images and powder X-ray diffraction characterizations proved that there was a“synergistic effect”between Ni and Fe,which was affected by N content.The synergetic effect could result from the formation of Fe Ni alloy as well as the decrease of metal particle sizes and the improvement of metal dispersion.Ni could improve the disperision of Fe and Fe could enhance the interactions between the support and Ni.Based on the experimental results,Ni Fe alloy could be speculated to play a crucial role in the CH of PPE and BPE,which was major active sites for the cleavage of C-O bond.On this basis,possible reaction pathways of the Ni_10%@Fe/NC_0.33-800catalyzed hydrogenolysis of BPE and PPE were proposed,respectively.The CH experiments of three lignins were performed over Ni10%@Fe/NC0.33-800.Compared with the non-CH（NCH）reaction,the results showed that the catalyst showed the best performance on the CH effect of DL.The conversion and liquid yield（LY）of DL increased by 27.9%and 25.3%under the reaction conditions of 300℃,1 MPa H₂,and 6 h,respectively.However,the conversion of AL and KL increased by 13.1%and19.8%,and the LY increased by 15.7%and 20.9%,respectively.Gas chromatography mass spectrometry analysis showed that group components in the liquild obtained from lignin hydrogenolysis were mainly composed of phenols,arenes,aromatic ketones,aromatic aldehydes,aromatic ethers,aromatic esters,aromatic alcohols,aromatic acids,aliphatic esters,alkyl alcohols,and alkyl ketones.The yields of both phenols and aromatic alcohols from CH of lignin over Ni_10%@Fe/NC_0.33-800 were obviously higher than those from NCH.In addition,the structural features of liquild products were further evaluated by 2D ¹H–¹³C HSQC nuclear magnetic resonance.Compared with NCH,the types of compounds generated by the cleavage ofβ-O-4,β-5 andβ-βbond in LP of CH were increased.These results suggested that Ni_10%@Fe/NC_0.33-800 could effectively cleave C-O bridges in DL,AL,and KL,which significantly promoted the formation of aromatic compounds such as phenols and aromatic alcohols.There are 66 figures,16 tables,and 108 references in this thesis.