Cleavage Of Lignin Aryl Ether Bonds Over Rhenium Oxides

Lignin is a unique polymer consisting of aromatic rings,which therefore becomes a major renewable source for bio-based products and aromatic chemicals.The efficient transformation of lignin into phenolic monomers and other high value-added chemicals remaina huge challenge due to the variability and the complexity of its irregular structure.In this approach,rhenium(Ⅶ)Oxide(Re2O7)and ReOx/AC were studied as catalysts for selective cleavage of lignin into aromatic compounds under mild conditions.The results in this thesis are summarized as follows:First,selectively catalytic conversion of a series of lignin β-O-4 model compounds and organosolv pine lignin into aromatic chemicals over Re2O7 in tetrahydrofuran under 1 MPa hydrogen pressure was developed.The optimum reaction conditions for depolymerization of ligninwere screened,resulting 76.3%yield of bio-oilThe catalytic mechanism over Re2O7 was proposed via NMR and GC-MS analysis.Second,supported ReOx/AC catalyst,a heterogeneous catalyst,was prepared by wetness-impregnation method.The highly selective cleavage of C-O bonds in typical lignin a-O-4 model compounds and the deconstruction alkali lignin into aromatic chemicals over ReOx/AC were described.The optimize reaction conditions for depolymerizing lignin by ReOx/AC were obtained through experimental conditions screening.The yield of bio-oil can reach 71.5%.ReⅣ-ⅥOx was detected as the active species through XPS and XAFS characterization for the catalyst before and after reaction.