Cu-catalyzed Selective Oxidation Of C/G-type Lignin To Oxygenated Aromatic Chemical

Lignin is a renewable aromatic polymer rich in nature with great potential to produce the high value-added chemicals and materials.Compared with G/S/H type lignin,C type of lignin is found in recent years to coffeol monomer by C-O and C-C bond benzo homopolymer,is considered to be lignin conversion preparation of the high value-added oxygen aromatic chemicals of an"ideal"raw material,the key to the efficient transformation is the C type of lignin C-O and C-C bond catalytic selection oxidation.In this paper develops Cu-based catalytic system and studies C/G lignin catalytic oxidation to oxygen-containing aromatic chemicals.The main research contents are as follows:（1）A strategy was proposed to catalyze C/G lignin oxidation by CuCl₂,converting C/G lignin lysis into four kinds of phenolic monomers:vanillaldehyde/acid and protocatechaldehyde/acid.Using CuCl₂catalyst in CH₃CN/H₂O（8/2,v/v）at 190℃for 4 h,the G and G-type linkages in lignin would be almost completely cleaved and transformed（based on 2D HSQC NMR and GPC characterizations）.The total C/G-type aromatic monomer yield was achieved at 60.8 mg/g（12.9 wt%based on Klason lignin）.The C-type aromatic monomers were yielded at 7.7 mg/g（1.6 wt%）at the initial 0.2 h and gradually decreased as the reaction proceeded.The instability of protocatechuic aldehyde and protocatechuic acid during the high-temperature reaction indicated that a more efficient catalytic oxidative system and milder reaction conditions would favor the production of the C-type aromatic monomers.（2）Non-precious metal MO_x/NC（Mn,Fe,Co,Mo,Cu）catalyzed the oxidation conversion of C/G lignin was studied.The results showed that commercial Pd/C catalysis produced a amount of C type monomer（the total yield of primary catechaldehyde/acid was 4.7 mg/g）,CuO_x/NC catalyzes more polyphenolic monomers,and the total yield of vanillin/acid,protocatechaldehyde/acid was 43.7 mg/g.The study of CuO_x/NC preparation method,catalyst quality and reaction time showed that:（i）the CuO_x/NC prepared by N₂atmosphere roasting after 800℃ of Cu（OAc）₂/Phen（1/2,mol/mol）was the best;（ⅱ）increased catalyst dosage or prolonged reaction time,the total yield of phenolic monomers tended to increase first and then decrease.2D HSQC NMR characterization revealed that CuO_x/NC catalyst can effectively oxidize C/G ligninβ-O-4,β-β,β-5 structural units and C-O or C-C bonds of benzoxyxy structural units to produce C/G type aromatic monomers such as vanillin/acid and protocatechaldehyde/acid.In this paper,it is found that CuCl₂ and CuO_x/NC can effectively catalyze the oxidative lysis of C/G type lignin C-O and C-C bonds and convert them into high value-added oxygenic aromatic chemicals such as vanillin/acid and protocatechaldehyde/acid,providing scientific understanding and technical means for the catalytic oxidative transformation of C/G type lignin.