Study On Catalyzing Cleavage Of C-O Bond In Lignin Model Compound By Vanadium-based Catalyst

Biomass energy,as an environment-friendly renewable energy source,is one of the effective alternative energy sources in the global energy crisis in the new century,the use of catalytic methods to convert renewable lignocellulose into value-added chemicals and biofuels,which is of vital importance and attraction to sustainable chemistry.Degradation of C-O bonds accounting for 67%-75%of lignin structure can realize the conversion of lignin biomass into fuel and chemical raw materials.However,the complex structure of lignin make its degradation and utilization still in its infancy,most of lignin is treated as waste,which can easily cause environmental pollution and resource waste.Therefore,it is very important to explore a high value utilization of lignin by exploring a high efficiency catalytic cracking C-O bond technique in lignin.Due to the difficult separation and purification of products after degradation.Firstly,lignin model compounds were selected for experiments to provide a theoretical basis for the catalytic degradation of lignin to understand and develop the processes involved in lignin catalytic transformation.In order to investigate the properties of catalyzing fracture of C-O bond in lignin model compounds,in this paper,2,6-dimethoxyphenol was used as lignin model compound,V/TiO₂catalyst was prepared by sol-gel method and bimetallic catalyst was prepared by impregnation method（V-X/TiO₂where X=Co,Cu,Ni）.Using V,V/TiO₂ and V-X/TiO₂ as catalysts,the properties of catalyzing break of C-O bond in 2,6-dimethoxyphenol were studied,The study found that:（1）when only distilled water was used as solvent and hydrogen supplier,the catalytic breaking of C-O bond in 2,6-dimethoxyphenol by vanadium（described briefly in the following article as V）showed obvious activity,and the main products were 3-methoxycatechol and pyrogallol.（2）The possible catalytic mechanism was as follows:the first step was that V first catalyzed the cleavage of C-O bonds in 2,6-dimethoxyphenol to form3-methoxycatechol;and then to catalyze the breaking of C-O bonds in 3-methoxycatechol to produce pyrogallol.The degradation rate of 2,6-dimethoxyphenol was 89.50%,proportion of pyrogallol was 43.38%,and the selectivity was 52.00%.（3）The introduction of TiO₂ in the catalyst could reduce carbonization and coking in the reaction process,and improved proportion and selectivity of pyrogallol to 57.58%and 68.90%.（4）Bimetallic catalyst can further improve the degradation rate of 2,6-dimethoxyphenol,degradation rate of 2,6-dimethoxyphenol can be further increased to 94.00%and the ratio of pyrogallol to 62.95%by bimetallic catalysts introducing Ni metals.Secondly,benzyl phenyl ether withα-O-4,the representative bonding form of lignin,was selected as the lignin model compound.It was found that:（1）compared with the catalytic degradation of 2,6-dimethoxyphenol under the same reaction conditions,V has obvious catalytic cracking performance forα-O-4 bonds in benzyl phenyl ether,the degradation rate was 96.74%,and the products were mainly 4-benzylphenol and 2-benzylphenol.（2）when n-propanol or n-butanol was used as the reaction solvent,V catalyzed the C-O bond of benzyl phenyl ether to break at the same time C-C bond to further obtain monophenolic compounds.（3）The activity of catalytic cleavage of C-O bond in benzyl phenyl ether decreased by V-based bimetallic catalyst that introducing Co、Cu、Ni.The results of XRD and SEM showed that Co,Cu,Ni and V form compounds supported on TiO₂ surface and pore channels resulted in the reduction of the catalyst’s specific surface area and the catalytic performance.but the degradation rate of V/Co-TiO₂、V/Cu-TiO₂、V/Ni-TiO₂ were reduced from 97.15%to 96.80%,94.55%and 92.57%respectively.The experimental results showed that vanadium-based catalysts showed obvious catalytic degradation on C-O bonds of lignin model compounds.The vanadium-based catalyst could catalyze breaking of C-O bond in lignin model compound as 2,6-dimethoxyphenol and benzyl phenyl ether under green catalytic system with distilled water as the reaction solvent,providing a certain research basis for the conversion of lignin into high value-added chemicals.