Theoretical Study On Hydrodeoxygenation Of Phenolic Compounds Over Ru-doped Fe Catalysts

In this thesis,density functional theory（DFT）calculations were performed to study the hydrodeoxygenation（HDO）mechanism of phenolic compounds over Ru-doped Fe catalyst.The structure-performance relationship of phenolic hydrodeoxygenation and the microcosmic nature of bimetal synergistic catalysis were discussed from the aspects of Ru doping method,Ru doping amount,and Fe-Ru bimetallic composition and structure.The computational results provide important theoretical basis for future design and synthesis of efficient HDO catalysts.The calculation results show that Ru doping promotes the dissociation of H₂ molecules on the Fe（211）surface and improves the hydrodeoxygenation reaction rate.The surface H*coverage has a small effect on the adsorption properties of phenolic compounds on the catalyst surface.On 1Ru-Fe（211）surfaces,the horizontal adsorption of phenolic reactants through the interaction between benzene ring and catalyst surface is more stable than the vertical adsorption through the interaction between hydroxyl group and catalyst surface.The adsorption of phenolic reactants on 1Ru_ads-Fe（211）is more stable than that on 1Ru_sub-Fe（211）,and the barriers of phenol and o-cresol dehydroxylation steps are reduced by 0.13 e V and 0.28 e V,respectively,leading to facile formation of the target aromatic products on 1Ru_ads-Fe（211）.The dominant route of guaiacol hydrodeoxygenation on 1Ru_sub-Fe（211）goes through first generation of phenol via demethoxidation,followed by phenol dehydroxylation to produce benzene（the rate-limiting barrier is 1.16 e V）.On the surface of 1Ru_ads-Fe（211）,the preferred pathway proceeds through guaiacol first dehydroxylation followed by demethylation to form phenol（the rate-limiting barrier is 1.21 e V）.Ru doping affects the surface structure and electronic properties of Fe catalyst,thus influencing the adsorption properties of phenolic reactants,hydrodeoxygenation path,and the catalytic performance.The effects of Ru doping amount on the adsorption activation and hydrodeoxygenation of phenolic compounds were also investigated.Compared to 1Ru_ads-Fe（211）catalyst,the deoxygenation barrier of C_Ar-O bond cleavage is increased by 0.75 e V on the 4Ru_ads-Fe（211）surface,thereof inhibiting benzene production.The direct hydrogenation barrier on the benzene ring and subsequent dehydroxylation barrier of the saturated benzene ring are lower than that of the direct deoxygenation of phenolic reactants via C_Ar-O bond breaking.On the 4Ru_ads-Fe（211）surface,phenolic reactants are more likely to convert into ring-saturated products such as cyclohexane through fast hydrogenation on the benzene ring.Increasing the Ru atom number to form cluster supported model of 4Ru_ads-Fe（211）can further improve the adsorption strength of phenolic reactants.Further increasing the doping amount of Ru can lead to the formation of alloy structure such as Fe Ru（111）,based on which the phenolic reactants are found to be more stably adsorbed than on the 1Ru_sub-Fe（211）surface.The calculation results reveal that doping Ru in Fe catalyst can modify the surface structure and electronic properties of the catalyst,and thus affects the adsorption and activation of reactant molecules as well as the hydrodeoxygenation performance.Doping a small amount of precious metal Ru into Fe catalysts in the form of surface adsorption is more conducive to the hydrodeoxygenation of phenolic compounds to aromatics.