Pd催化木质素醚类二聚体分子内氢转移断裂C—O键研究  

Supported Pd Catalysts for the C—O Cleavage of the Lignin Derived Model Dimers through Intramolecular Hydrogenolysis Reaction

作　　者：严龙[1] 庞欢[1] 黄耀兵[2] 傅尧[1] 

机构地区：[1]安徽省生物质洁净能源重点实验室化学与材料科学学院中国科学技术大学,合肥230026 [2]南京林业大学化学工程学院,南京210037

出　　处：《化学学报》2014年第9期1005-1011,共7页Acta Chimica Sinica

基　　金：973计划(Nos.2012CB215306;2013CB228103);国家自然科学基金(Nos.21325208;21361140372;21172209);教育部中央高校基本科研业务费专项(No.WK2060190025);高等学校博士点基金(No.20123402130008);中国科学院基金(No.KJCX2-EW-J02);霍英东教育基金资助~~

摘　　要：结合氢转移方法,研究了木质素模型物2-(2'-甲氧基苯氧基)-1-苯乙醇(1a)分子在无外加氢源的条件下利用金属钯催化剂催化发生C—O键断裂反应.合成并表征了一系列Pd负载型催化剂,通过优化发现反应体系在环己烷溶剂和弱碱添加剂Na2HPO4条件下显示出较好的催化效率.结合反应特点将催化剂进行改进,使用MgO作为载体的催化剂Pd/MgO高效完成了木质素模型物的分子自供氢降解.反应过程可能分为两步进行:首先,模型物在钯表面先进行脱氢过程,含羟基的木质素模型物二聚体1a脱去氢后生成酮式中间体2-(2'-甲氧基苯氧基)-1-苯乙酮(1b),被脱去的氢原子吸附于钯表面.随后,脱氢中间体1b在Pd催化下与其表面吸附的H作用,发生催化C—O键断键过程.The selective depolymerization of the C—O ether bonds in lignin has attracted considerable attentions which would facilitate the valorization of lignin. The model compounds with β-O-4 type ether bonds were the most frequently studied molecules. In this study, we used 2-（2-methoxyphenyl）oxy-1-phenethanol（1a） as model compound for the C—O cleavage through intramolecular hydrogenolysis reaction. The hydroxymethyl group acted as the hydrogen source by dehydrogenating over Pd catalysts. Then, the cleavage of C—O bond takes place on the supported Pd catalyst with Pd-H active species. All the catalysts were prepared and characterized by XRD, TEM and BET. Among different metal catalysts, Pd catalysts gave best results toward the C—O bond cleavage reaction. After that, the influences of solvent were studied and the best solvent was cyclohexane. Different additives such as acids and bases were also tested in the model reaction. The strong base（i.e. KOH） showed negative effect on the product yield, but a weak base（i.e. Na2HPO4） gave a promotion effect on the reaction. The result indicated that the modification of the Pd catalysts＇ supports would be a good option for the C—O bond cleavage reaction. Thus, different Pd catalysts with different supporting materials were prepared and tested, and found that MgO, a weak basic support, gave promoted performance on this reaction. Finally, to figure out the reaction pathway, the reaction mixtures with different reaction time were analyzed by GC-MS which showed that the ketone was the main intermediate of the reaction. The result indicated that the main route for the intramolecular hydrogenolysis reaction was（1） the dehydrogenation of –CCHOH to ketone to form Pd-H species and then（2） the C—O bond was cleavage by the Pd-H species to form the depolymerization products.

关 键 词：木质素 解聚 Pd催化反应 C—O键切断 氢转移 

分 类 号：O621.13[理学—有机化学]