Study On Catalytic Hydrodeoxygenation Of Vanillin As Model Compound Of Bio-oil With Short-chain Aliphatic Alcohol Hydrogen Donor

Nowadays,the tense relationship between the supply and demand of energy has attracted much attention,as well as the serious environment problems such as global warming and atmospheric contamination.Energetically developing the renewable energy as an alternative for fossil fuels is urgent and significant to realize the sustainable development goals.Bio-oil,as a renewable fuel,is a promising bio-crude produced from biomass feedstocks undergoing thermochemical process.However,utilizing raw bio-oil is difficult,mainly due to its undesired characteristics such as high oxygen and water content,high corrosiveness and thermal instability.Bio-oil must be further upgraded and deoxygenated before it can be co-fed into a petroleum refinery.Hydrodeoxygenation（HDO）,among many different upgrading procedures,is considered effective for the deoxygenation of hydrocarbons in bio-oil by catalytically removing oxygen atoms as water.Various oxygen-containing compounds existing in bio-oil make it difficult to understand the reaction pathways during the HDO process.Vanillin,containing three different oxygenic groups,which is a typical model compound of pyrolysis oil from lignin,is regraded as a good condidate for examining the effect of HDO on bio-oil upgrading.Hydrogen is a reactant in HDO reaction,thus,special equipment is required to keep high pressure and prevent gas leakage due to the high flammability of hydrogen gas in contact with air,which incurs a hefty infrastructure cost on the industrial scale.Additionally,hydrogen is consumed largely in this reaction,while molecular hydrogen production is a costly industrial process.Therefore,short-chain aliphatic alcohol,due to its availability,low price and high safety,is an environmental-friendly hydrogen source to replace hydrogen gas in HDO reaction.In this dissertation,the catalytic property was investigated using short-chain aliphatic alcohol as hydrogen donor for the hydrodeoxygenation（HDO）of vanillin over Pt/Ce_0.5M_0.5O₂（M=Zr,Ti）catalysts and Mo₂C/AC catalysts,beside the reaction pathways and activities of these two different types of catalysts.The main results are presented as follows:（1）Mixed oxides Ce_0.5M_0.5O₂（M=Zr,Ti）with high hydrothermal stability were prepared by the coprecipitation and sol-gel method,and highly dispersed Pt/Ce_0.5M_0.5O₂（M=Zr,Ti）catalysts were effectively synthesized by impregnation.It was found that mixed oxides Ce_0.5M_0.5O₂（M=Zr,Ti）were the supports with high hydrothermal stability,and the catalytic activity of Pt/Ce0.sZr0.502 for the HDO of vanillin was superior to that of Pt/Ce_0.5Ti_0.5O₂.The catalytic property was mainly attributed to the surface acidity and the highly dispersed Pt supported on the catalyst.These short-chain aliphatic alcohols were the hydrogenous organic small molecules,and used as the ideal and effective hydrogen donors.（2）The short-chain aliphatic alcohols acted as the solvents in HDO reaction catalyzed by Pt/Ce_0.5Zr_0.5O₂.The polarities and acidities of the solvents had different effects on the overall process,compared to the HDO reaction with hydrogen molecules.It was shown that high polarity of the solvent tended to the hydrogenation of C=O bond,probably due to the strong absorption between solvent and the catalyst which could change the surface of the catalyst.Meanwhile,the alcohols were also the protonic solvents,and the high acidity represented the strong ability to donate the active proton which was beneficial to the process of hydrogenation.Methanol which had the highest polarity and acidity performed best among all the short chain alcohols in HDO reaction,thus,the conversion of vanillin reached 99.3%,and the selectivity of 2-methoxy-4-methylphenol was 80.6%.（3）A series of Mo₂C/AC catalysts were prepared by "carbothermal hydrogen reduction"（CHR）method.Molybdenum carbide nanoparticles highly dispersed on the surface of activated carbon as an effective catalyst for the HDO of vanillin with short-chain alcohol as hydrogen donor.It was found that the reaction pathways of vanillin catalyzed by Mo₂C/AC and Pt/Ce_0.5M_0.5O₂（M=Zr,Ti）were different.With ethanol as hydrogen donor,the hydrogenation of vanillin to produce 2-methoxy-4-methylphenol was the main reaction catalyzed by Mo₂C/AC,while vanillin preferred to convert into guaiacol undergoing the decarbonylation by hydrogenolysis of the C-C bond catalyzed by Pt based catalysts.The production of guaiacol compared to 2-methoxy-4-methylphenol had less atom economy for the loss of another carbon atom,however,the conversion of vanillin was poor.The effect of different reaction conditions on the catalyzed hydrodeoxgenation of vanillin by Mo₂C/AC catalyst were investigated systemically in order to improve the conversion ratio.With ethanol as hydrogen donor,the optimal reaction conditions were:with catalyst loading of 20%,the reaction temperature was 200°C and reaction time was 5 hours.After the recycle of 20%Mo₂C/AC catalyst,the conversion of vanillin and selectivity of 2-methoxy-4-methylphenol seemed to have no apparent changes,indicating that the activity of Mo₂C/AC catalyst was stable,mainly depended on the highly dispersed P-Mo₂C nanoparticles of the catalyst.