| Lignin is an important renewable biomass resource.Based on the concept of green chemistry and considering energy saving,environmental protection,safety and other factors,this paper developed a method of high-value utilization of lignin.Through preparation,optimization and characterization,the nickel-based catalyst with the highest photocatalytic activity was selected,and the visible light photocatalytic lignin model compounds and real lignin were studied,and aromatic monomer products with high utilization value were obtained under mild conditions.(Normal temperature and pressure)Achieve high selectivity and high conversion rate,at the same time in-depth study of the photocatalytic reaction system and mechanism.This paper mainly includes the following contents:(1)This subject has made a series of preparation,screening,optimization and characterization around nickel-based catalysts.First,a comparative experiment shows that the nickel-based catalysts has photocatalytic activity without precious metal doping.In the process of examining the most suitable catalyst carrier,the catalyst with Al2O3,MgO,and ZrO2 as the carrier showed the best photocatalytic activity.The optimal nickel loading and reduction temperature were further investigated.10%is the optimal nickel loading and 600℃ is the most suitable reduction temperature.Various characterization methods revealed the effect of reduction temperature on the catalytic activity of nickel.(2)This subject further explores the effects of various factors in the reaction system on photocatalytic cracking.The first is to explore the influence of the solvents and additive on reaction system separately.Taking the benzyl phenyl ether lignin model compound as an example,commonly used alcohol solvents have a hydrogen donating effect on the photocatalytic reaction,and sec-butanol is the best hydrogen donating solvent.When hydrazine hydrate replaced NaOH as an additive,its catalytic conversion rate increased significantly from 66%to 96%,indicating that hydrazine hydrate additive has a more obvious promotion effect.Nickel-based catalysts have different catalytic activities for different types of C-O aryl ether bonds and aromatic monomer structures.This topic is aimed at 9 model compounds(BPE,PEB,DPE,PPOL,GE,MMP,DMP,HMP,HDMP).A photocatalytic reaction was carried out,showing that the nickel catalyst has photocatalytic activity for various types of C-O aryl ether bonds.Furthermore,the degree of the photocatalytic reaction under different light sources is investigated.The stronger the light intensity,the higher the conversion rate.When natural light is used and no energy is consumed,the β-O-4 bond can also be partially broken.(3)Real lignin contains a large amount of C-O aryl ether bonds.After exploring the photocatalytic activity of C-O aryl ether bonds,this topic explores the photocatalytic cracking of real lignin.Experiments show that under mild reaction condition(room temperature and atmospheric pressure),the nickel-based catalyst catalyzes the lignin structural unit.The main occurrence of C-O aryl ether bond breaks.The main products are guaiacol,vanillin,BHT,and vanillyl alcohol.There are no products of excessive hydrogenation of benzene rings.Achieved high conversion and high selectivity under mild reaction conditions.Lignin can achieve a degradation rate of 68%under natural light without energy consumption,indicating that the real lignin macromolecular structure can also achieve photocatalytic reactions at normal temperature and pressure.This study provides a new idea based on green chemistry for the high-value utilization of lignin.It is a potential industrial application that can achieve low energy consumption,high selectivity,and high conversion rate.The C-O aryl ether bond is a functional group of a large class of important chemical raw materials and pharmaceutical intermediates.This study has also greatly expanded the application range of the photocatalytic activity of nickel-based catalysts. |
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