Studies On The Catalytic C-O And C-C Bonds Activation Of Biomass Molecules For Oxygen-containing Chemicals Production

The utilization of biomass resources will be of great importance to the sustainable development of human society.As the most abundant biomass resource,lignocellulose presents dominant C-O and C-C bonds structure.It is feasible to prepare high-value chemicals by directional shearing and conversion of C-O and C-C bonds in biomass molecular structural units,however,there remains great challenges.This thesis focuses on the catalytic C-O and C-C bonds activation of biomass molecules for the purpose of exploring and developing simple and efficient strategies to achieve high-efficiency catalytic conversion of biomass feedstock into valuable chemicals such as aromatic compounds,adipic acid,etc.The first part of this thesis focuses on the development of the photocatalytic strategy for the lignin and its model compounds C-O and C-C bonds depolymerization under simulated solar irirradiation to obtain high value-added aromatic compounds.Two kinds of photocatalysts system for the selective cleavage of C-O or C-C bonds in lignin were exploited in this thesis.First,we found the lignol β-O-4 bond could be fragemented selectively by sulfide photocatalysts(such as CdS,Zn_mIn₂S_m+3)into phenolic derivatives with high yields,what’s more,this strategy could be directly applied to the photocatalytic depolymerization of organosolv lignin to obtain valuable aromatic monomers.Mechanism investigations on the lignol β-O-4 model indicated that the formation of a benzyl radical intermediate from hydrogen abstraction of Cα-H from β-O-4 model compound was the key step.In addition,the performance of photocatalytic cleavage of P-O-4 C-O bond could be further improved by a band gap engineering strategy for Zn_mIn₂S_m+3（ZIS）solid solution photocatalysts,a positive correlation between the ability of photocatalytic H-abstraction of Ca-H and catalysts’valence oxidizing potential is revealed.Besides,the SH groups on photocatalysts surface were verified to be indispensable for triggering the H-abstraction reaction by the generation of S*radical.On the other hand,apart from β-O-4 linkage,the β-1 linkage also constitutes a significant portion of lignin linkages.However,due to the chemical inertness of C-C bond,there are very scarce methods for the β-1 C-C bond cleavage,which results in the recalcitrance of lignin for its complete conversion to aromatic products.In the work of this thesis,an efficient strategy for the selective cleavage of β-1 lignin models to aldehydes under simulated solar irirradiation using Ag₃PO₄-C₃N₄ composite photocatalyst was developed.Mechanism investigations found the carbon radical intermediate generated by holes oxidation of Cp-H interacted with superoxide anion,resulting in C-C bonds cleavage.66%-95%yields of aromatic aldehydes were obtained from various substrates in this photocatalyst system.The second part of this thesis focuses on the preparation of the bulk chemical adipic acid by the dehydroxylation of glucaric acid originating from biomass cellulose.By investigating the performance of various transition metal oxide catalysts for the dehydroxylation of glucaric acid,it was found that the rhenium catalyst has an unique and excellent catalytic deoxydehydration（DODH）reactivity.Then,we have tried and developed a heterogeneous rhenium catalysts system for the dehydroxylation of glucaric acid and found that the ReO_x/ZrO₂ catalyst exhibited the best catalytic performance,affording DODH products in 93%overall yield with 41%yield of completely dehydroxylation products.Mechanism investigation found catalyst supports could affect the redox properity of[ReO_x]species and controlled its activity for C-O cleavage.The rhenium species may undergo a redox process between Re（Ⅵ）and Re（Ⅳ）.In addition,by coupling with hydrogenation steps using commercial Pd/C as the catalyst,the alkene intermediates can be completely converted into the adipate product with 82% yield.