Preparation Of Ru And Ni Catalysts And Research On Degradation Of Lignin Model Compounds

As the second natural organic compound in nature,lignin accounts for 15%-30%of lignocellulose.The content is only the same as cellulose.It is rich in complex aromatic compounds.Lignin is very important in the field of biomass.Large application potential is expected to replace fossil energy sources and produce aromatic compounds as raw materials.Lignin is polymerized by three monomer units(sinapyl alcohol,coniferyl alcohol and p-coumarol)connected by C-C and C-O bonds through a free radical coupling reaction.The C-O ether bonds in lignin account for 67-75%,of which 4-O-5 accounts for 4-9% of the lignin ether part,?-O-4 and?-O-4 are about 45-62% and 3-12%respectively.The structure of lignin is relatively complex and the C-O bond is relatively stabilization,the degradation of lignin still presents a very big challenge.The metal catalysts used in the degradation of lignin mainly include noble metal catalysts and transition metal catalysts.The transition metal catalysts mainly include Cu,Co,Fe,Ni,especially Ni.Ni catalyst has superior selectivity in the cleavage of C-O bonds.However,under high temperature conditions,Ni catalysts are easy to sinter and have poor carbon deposit stability and activity.Therefore,further improvements are needed in nickel catalysts.Noble metals such as Pt,Pd,Rh and Ru have excellent catalysis,but too strong hydrogenation capacity will further reduce the benzene ring,which is unfavorable for the degradation of lignin.Bimetallic catalysts can produce synergistic effects and can improve the single metal Catalyst selectivity and activity overcome the shortcomings of single metal catalysts.In addition,the influence of the carrier on the reaction is also particularly important.This paper mainly studies the basic research and application of the hydrodeoxygenation reaction of Ru and Ni metal catalysts in the four model compounds of lignin and the application research of the degradation reaction of natural lignin.Mainly synthesize different single metal catalysts and different supported catalysts,as well as different supported bimetallic catalysts,to study the degradation reaction process of lignin and the performance of the catalyst.The main work content is as follows:(1)Pd/AC,Ru/AC,Fe/AC,Ni/AC catalysts were prepared by equal volume impregnation method and chemical reduction method,and the catalyst structure was analyzed by BET,XRD,XPS,SEM,TEM and other characterization methods In the characterization and application of the reaction with three model compounds of lignin(diphenyl ether,benzyl phenyl ether,phenoxy ethylbenzene),the reaction results found that the hydrogenation activity Ru>Pd,Ni>Fe,the choice of aromatic compounds In terms of nature,Pd>Ru,Ni>Fe.The effects of the reaction conditions of Ru/AC and Ni/AC catalysts on the three lignin model compounds of diphenyl ether,benzyl phenyl ether and phenoxy ethyl benzene were studied in detail.The higher the temperature,the lower the activity of the catalyst.The effect of hydrogen pressure and time on the product is mainly due to the product content of aromatic compounds.The greater the pressure and time,the aromatic compounds will gradually decrease.Moreover,the conversion rate of Ru/AC catalyst is generally high,and the conversion rate of Ni/AC catalyst is relatively low.However,Ni/AC has better catalytic selectivity,and changes in reaction conditions have little influence on output.(2)The molecular sieve HZSM-5 catalyst support was synthesized by hydrothermal synthesis method,and different supports HZSM-5,ZSM-5,Nb₂O₅,Ti O₂,and NbAlS-1,Ru and Ni single metal catalyst were prepared by equivalent-volume impregnation and chemical reduction method.Metal catalyst,and the structure of the catalyst was characterized by BET,XRD,XPS,SEM and other characterization methods.It was found that the four carrier species are rich in acidity.Among them,HZSM-5 and ZSM-5 contain Bronsted acid and Lewis acid,Nb₂O₅and Ti O₂carriers are rich in Lewis acids.In the reaction of lignin model compounds,it was found that a catalyst carrier rich in Bronsted acidity can effectively improve the selectivity of aromatic compounds,and a carrier rich in Lewis acidity can promote further hydrogenation reactions.In addition,a new type of NbAlS-1 molecular sieve carrier with adjustable acidity was synthesized.The Ru/NbAlS-1 and Ni/NbAlS-1catalysts were synthesized and applied to the lignin model compound reaction species to have a higher conversion rate.Adjusting the ratio of acidity can make the product obtain more aromatic compounds.(3)HZSM-5 molecular sieve was synthesized by hydrothermal synthesis method,and Ni Ru bimetallic catalysts with different carriers HZSM-5,ZSM-5,Nb₂O₅,Ti O₂were prepared by equivalent-volume impregnation and chemical reduction method,and through BET,XRD,XPS,SEM and other characterization methods.Catalyst applied to the reaction study of lignin model compounds.The effect of different metal contents of Ni and Ru on the reaction is studied in detail.Research have shown that the addition of Ru metal can resultfully enhancement the reaction,maintain the activity of the reaction and the high selectivity of Ni to C-O bond cleavage,and the hydrogenation reduction of the benzene ring can be inhibited.In addition,comparing different bimetallic catalyst supports,it is found that HZSM-5 has good aromatic compound selectivity.Finally,lignin was extracted from poplar wood by a fast and low-temperature method,and characterized by FTIR,NMR,SEM,etc.It was found that the extracted lignin has a complete structure without introducing other functional groups,and the size is small,which is conducive to the reaction.Finally,the Ni-Ru/HZSM-5 bimetallic catalyst was applied to the catalytic degradation reaction of poplar lignin,the conversion rate reached 35.4%,the yield of small molecule compounds reached 26.3%,and the yield of lignin structural derivatives It reached 9.1%,and the yield of aromatic compounds reached 28.16%.