Hydrogenation Of Biomass Platform Compounds Over Metal Nanoparticles Stabilized By Lignin Derivatives

Lignin,as a renewable biomass resource with rich reserves and high aromatic ring content,has attracted much attention.However,due to its complex molecular structure,the effective utilization rate is less than 5%,which is an urgent problem to be solved in the field of biomass utilization.The research shows that the abundant oxygen-containing functional groups in lignin structure can provide effective sites,and the main structure of aromatic ring can provide a more stable framework,which makes lignin have the potential to be used as catalyst matrix.If lignin can be applied to the catalytic conversion process of biomass after processing and modification,it will be conducive to the green closed-loop production of"from biomass to biomass".Aiming at the hydrogenation value-added reaction process of vanillin and levulinic acid,two representative industrial platform products in the conversion of lignocellulose,two kinds of metal nanoparticle catalysts stabilized by lignin derivatives were designed and prepared,and their catalytic performance in the hydrodeoxygenation of vanillin to 2-methoxy-4-methylphenol and the hydrogenation of levulinic acid toγ-valerolactone were studied respectively:（1）Aqueous-phase reduction-stabilized Pd nanoparticles（Pd NPs）catalysts for the hydrodeoxygenation of vanillin:Sodium lignosulfonate（SLS）,a waste product from paper black liquor,was used as the reducing and stabilizing agent to investigate its ability to reduce and stabilize different metal salt precursors in the aqueous-phase system,and the catalytic ability of the prepared aqueous-phase NPs system for the hydrodeoxygenation reaction of vanillin.By optimizing the conditions of metal salt precursors,preparation temperature,SLS concentration and stirring speed,combined with the characterization results of UV-Vis,FT-IR,XRD,XPS and TEM,the Pd NPs with an average particle size of 14.63 nm were selected as the best catalyst for the hydrodeoxygenation of vanillin.The reaction was carried out at n_{（Vanillin）}/n_（Pd）=300,1mmol vanillin,1 MPa H₂,and 70°C for 2 h.The conversion of vanillin could reach 99.8%and the selectivity of the target product 2-methoxy-4-methylphenol（MMP）reached98.5%.The target product has a low solubility in water,and its self separation from the catalytic system could be achieved by standing after the reaction.The aqueous-phase catalytic system also showed good cycling stability,and the conversion of vanillin was always maintained above 98%after 10 cycles of reuse under the optimized hydrodeoxygenation process;while the selectivity of MMP was maintained above 92%after 5 cycles,and still reached 85.4%after 10 cycles of reuse.（2）Preparation ofγ-valerolactone by hydrogenation of levulinic acid catalyzed by lignin based hydrothermal carbon supported Ru:Based on the fact that the nano particle system reduced and stabilized by SLS is difficult to effectively catalyze the hydrogenation of levulinic acid,a hydrothermal carbon material with high loading performance is obtained by hydrolysis-hydrothermal-activation three-step method with sodium lignosulfonate as raw material,and Ru is loaded on its surface through impregnation and reduction to prepare a new lignin based catalyst.The effects of hydrothermal synthesis process,impregnation loading conditions and the amount of metal salt on the performance of the catalyst in promoting the hydrogenation of levulinic acid were investigated.The optimized Ru/LHC-0.2A catalyst could get 98.4%levulinic acid conversion and 98.5%γ-valerolactone selectivity under the conditions of 10 mmol levulinic acid with 30 mg catalyst dosage,1 m L water,70℃,2 MPa initial hydrogen pressure for 2 h.It is much higher than the catalytic ability of commercial Ru/C under the same conditions.Characterizations of TEM,SEM,N₂ adsorption-desorption,XRD,FT-IR,TEM,XPS,and Raman showed that the increase of amorphous carbon proportion and carbon defects in the carrier material is the favorable condition for effectively Ru metal loading.The effects of catalyst dosage,solvent water dosage,reaction temperature,reaction pressure and reaction time on the catalytic performance of Ru/LHC-0.2A in the hydrogenation reaction of levulinic acid were further studied.Under the mild process conditions of 20 mg Ru/LHC-0.2A,10 mmol levulinic acid,5 m L of water,80℃,initial hydrogen pressure of 1.5 MPa for 2 h,99.3%levulinic acid conversion and 98.9%γ-valerolactone selectivity could be obtained.The catalyst also has good stability,and the conversion of levulinic acid was still above 90%and the selectivity ofγ-valerolactone was always higher than 95%after 5 times of reuse under the optimized conditions.