活性碳上羧酸根锚定AuCl3催化乙炔氢氯化反应的理论研究  

A theoretical investigation of acetylene hydrochlorination catalyzed by AuCl3-anchored by carboxylic group on activated carbon

作　　者：张冠如 宁利超 谭凯 吕鑫 ZHANG Guanru;NING Lichao;TAN Kai;Lü Xin(College of Chemistry and Chemical Engineering,Xiamen University,Xiamen 361005,China)

机构地区：[1]厦门大学化学化工学院

出　　处：《厦门大学学报（自然科学版）》2019年第4期464-470,共7页Journal of Xiamen University：Natural Science

基　　金：国家自然科学基金(91545105,21273177)

摘　　要：采用密度泛函的B3LYP方法,运用分子模型对活性碳(AC)上羧酸根负载AuClx催化剂的活性结构、稳定性以及催化乙炔氢氯化的反应机制进行了理论探讨:结果表明:AuCl3催化剂可以被表面羧酸根单原子级分散锚定,形成AC-COOH-AuCl3表面活性中心,进而在氢氯化过程中与乙炔发生协同加成反应生成氯乙烯;同时形成具有螯合结构的表面活性中心AC-CO2>AuCl2,进而催化遵循分步反应异步加成机制的氢氯化反应,即乙炔活化吸附到Au(Ⅲ)中心,HCl异裂亲核加成到乙炔伴随羧酸根质子化,分子内质子迁移形成Au(Ⅲ)-氯乙烯d-π配键络合物,脱除氯乙烯恢复AC-CO2>AuCl2螯合结构.计算还表明,AC-COOH-AuCl3表面活性中心比Au2Cl6催化组分更不易与乙炔发生Au(Ⅲ)→Au(Ⅰ)的还原反应.By means of density functional theory B3LYP and molecular models,we have explored theoretically the possible structures and stability of active catalytic center(s)on AuClxcatalyst supported on the carboxylic group-containing activated carbon(AC)and the catalyzing mechanism of acetylene hydrochlorination.Single-atomic-level dispersion of Au(Ⅲ)catalyst can be achieved by coordinating to carboxylic group(-COOH)available on AC,forming such surface species as AC-COOH-AuCl3 with very low tendency of AuCl3 aggregation.Such surface species can react with acetylene following a concerted addition mechanism to release vinyl chloride(VCM)and to form another surface species AC-CO2>AuCl2,in which the Au(Ⅲ)center is chelated by the carboxylic group.The AC-CO2>AuCl2 is quite active in catalyzing acetylene hydrochlorination following a stepwise/asynchronous addition mechanism,i.e.,activated chemisorption of acetylene onto the Au(Ⅲ)center,nucleophilic addition of chlorine to acetylene with protonation of carboxylic group,intramolecular proton transfer to form Au(Ⅲ)-VCM d-π complex,and finally release of VCM with resumption of the AC-CO2>AuCl2 species.In addition,the computations disclosed that the tendency of Au(Ⅲ)being reduced to Au(Ⅰ)by acetylene is lower in AC-COOH-AuCl3 than in Au2Cl6.

关 键 词：乙炔氢氯化反应 活性碳 羧酸基团 AuCl3 

分 类 号：O643.12[理学—物理化学]