Low-Temperature Selective Hydrogenation Of Lignin-Derived Aromatics Catalyzed By Nitrogen-Doped Carbon Supported Ru-Fe Bimetallic Nanoparticles

Lignin derivatives with natural aromatic ring structure have great potential for conversion to aromatics and cycloalkanes for the production of chemicals and liquid fuels.Developing efficient catalysts with high activity and selectivity for hydrogenation of lignin-derived aromatics under mild conditions to obtain high-value added chemicals and clean liquid fuels is a significant step for lignin valorization.In this study,a well-dispersed Ru-Fe bimetallic nanoparticle catalyst supported on porous nitrogen-doped carbon（NDC）was developed through a simple impregnation method.Based on the catalytic hydrogenation of phenyl benzyl ether（BPE）,the effects of different precursors,N/C ratio,calcination temperature and Fe loading on the performance of the catalyst were investigated.The optimal conditions for catalyst preparation were screened out as follows:C₆H₉O₆Ru as ruthenium source,Fe（NO₃）₃·9H₂O as iron source,0.34 of N/C ratio,calcination temperature at 700 ^oC and 5%of Fe loading.In order to further understanding the physicochemical properties of the catalyst,X-ray diffraction,N₂adsorption-desorption,scanning electron microscopy and high-resolution transmission electron microscope were used to characterize the structural properties of Ru Fe/NDC catalysts.X-ray photoelectron spectroscopy was used to reveal the effects of elemental chemical valence states and N/C ratios in the Ru Fe/NDC on the catalytic hydrogenation performance of BPE.Hydrogen temperature programmed reduction was used to analyze the effect of Fe addition on the interaction between the support and the active component Ru and the change of the chemical environment around NDC.The magnetic properties of the catalyst were tested by vibrating sample magnetometry to explore the effect of Fe on the recovery performance of the catalyst.Ru Fe/NDC₇₀₀ showed excellent catalytic activity for hydrogenation of lignin-derived aromatics,such as diaryl ethers,phenolic monomers and arenes to corresponding alicyclic compounds with high selectivity under mild conditions.Combined with the product distribution of catalytic hydrogenation of lignin-derived aromatic dimers and density functional theory calculation,a possible reaction path for catalytic hydrogenation of aromatic dimer was proposed.BPE,a lignin-derived aromatic dimer,was completely converted at 30 ^oC,1 MPa H₂ and 2 h to obtain corresponding alicyclic ether with a selectivity up to 93%,2-phenylethyl phenyl ether and diphenyl ether were completely converted at 40 ^oC,1 MPa H₂ and 2 h,and the selectivity of 2-cyclohexyl ethoxycyclohexane and cyclohexyl ether was 97%and65.4%,respectively.Under the conditions of 50 ^oC,1 MPa H₂ and 2 h,guaiacol was completely converted and the selectivity of 2-methoxycyclohexanol reached up to89.4%.Toluene was completely converted into methylcyclohexane at room temperature.The catalytic hydrogenation performance of other lignin-derived aromatics was carried out at 50 ^oC and 1 MPa H₂,and the results showed that more than 30 lignin-derived aromatics could be completely converted into corresponding alicyclic compounds,indicating that the catalyst had a wide applicability.Ru Fe/NDC₇₀₀ also showed good activity in the catalytic hydrogenation of lignin oil.The main compounds detected by gas chromatography-mass spectrometry（GC-MS）in lignin oil and its hydrogenation products include phenols,aromatic ethers,aromatic ketones,cyclohexanols,aromatic aldehydes,aromatic esters,alkenes,alkyl esters,alkyl ketones and alkanols.The reaction conditions of catalytic hydrogenation of lignin oil were optimized.Under optimal reaction conditions（90 ^oC,2 MPa H₂ and 24 h）,most phenolic compounds in the raw lignin oil were converted into cyclohexanol and its derivatives,and the relative content of phenols decreased from 54.8%to 4.8%,while the relative content of cyclohexanols increased from 11.0%to 53.3%through catalytic hydrogenation.GC-MS and Fourier transform infrared spectroscopy were used to analyze lignin oil and its hydrogenation products under optimal conditions.The results showed that Ru Fe/NDC₇₀₀ could effectively catalyze the selective hydrogenation of aromatic compounds in lignin oil,especially phenols,and could significantly improve the hydrogen/carbon ratio of lignin oil.This thesis has 49 pictures,21 tables and 114 references.