Study On The Selective Catalytic Oxidation Of Cα Alcohol Lignin Model Compounds

With the increasing scarcity of fossil resources on the earth,lignin,as an abundant and renewable energy source,has a very broad development prospect in the conversion to biofuels and high value-added chemical products.In this thesis,the lignin monomer model compound 1-phenylethyl alcohol containing Cα alcohol,and the dimer model compound containing β-O-4 bond were used as research objects to explore an effective way to promote selective oxidation of lignin.Firstly,MoVNbOx composite oxide catalysts,which have high selectivite activities to secondary alcohols,were synthesized.After calcined at different temperatures,the catalysts were characterized by XRD,SEM,EDS and physical adsorption-desorption tests.The results showed that the intensity of the corresponding X-ray diffraction peaks increased with the increase of the calcination temperature of MoVNbOx catalyst,and the conversion of 1-phenylethanol increased from 43.7%to 60.7%.At the same time,with the increase of the amount of H2O2 in the reaction system,the conversion of 1-phenylethanol increased linearly.When the amount of H2O2 in the reaction system reached 7 ml/2.5 mmol reaction substrate,the conversion of 1-phenylethanol reached 82.2%.In addition,after the MoVNbOx catalyst was used for 3 times,the conversion of 1-phenylethanol was almost unchanged and stabilized at about 80%,indicating that the catalyst has good catalytic stability.Secondly,when the MoVNbOx catalyst was used in the oxidation reaction of lignin dimer,the mechanism of the oxidation-cleavage one-step reaction of the lignin model substrate depolymerization was proposed.During the catalytic reaction,the α-OH of the dimer compound was first oxidized by MoVNbOx catalyst to obtain the Ca ketone,this structure can reduce the adjacent β-O-4 ether bond energy,and then the oxidized model compound was further catalyzed by the catalyst to break the β-O-4 and C-C bond to obtain aromatic monomer compounds.With the MoVNbOx catalyst,oxidative depolymerization of lignin dimer was achieved under room temperature and atmospheric pressure,the conversion rate of lignin dimer and the yield of aromatic monomer were 88.8%and 84.7%,respectively.Finally,in the experiment of modifying the MoVNbOx catalyst,the Mo/V molar ratio and the Nb loading in the catalyst were changed to explore the optimal ratio of element combination,and loaded MoVNbOx on the nano-TiO2 to increase the specific surface area of the MoVNbOx catalyst.At the same time,the activity of the catalyst was also investigated by 1-phenylethanol conversion on MoVNbOx/TiO2 catalyst.The results showed that the catalyst with the best catalytic activity was M00.61V0.31Nb0.08Ox/TiO2.In addition,the optimum conditions for the selective oxidation of 1-phenylethanol were obtained as 0.1 g catalyst with 7 ml H2O2/2.5 mmol reaction substrate,and reacting for 5 hours at 80℃.The conversion rate of the lignin monomer model compound 1-phenylethanol can reach 86.5%.In the thesis,a series of MoVNbOx composite oxide catalysts were studied for selective oxidative dehydrogenation of secondary alcohol lignin model compounds.The catalysts showed good catalytic oxidation activities for lignin monomers and dimers with Ca secondary alcohol group.Moreover,changing the main composition of Mo,V,Nb could affect the conversion rate of ODH reaction.The oxidative dehydrogenation mechanism of the catalysts and the oxidation-cleavage reaction mechanism of the dimers were explored,which provided basic data for further research on the high value utilization of lignin.