Styrene epoxidation catalyzed by polyoxometalate/quaternary ammonium phase transfer catalysts: The effect of cation size and catalyst deactivation mechanism  

作　　者：Qiongna Xiao Yuyan Jiang Weiqiang Yuan Jingjing Chen Haohong Li Huidong Zheng 

机构地区：[1]College of Chemical Engineering,Fuzhou University,Fuzhou 350116,China [2]Qingyuan Innovation Laboratory,Quanzhou 362801,China [3]Engineering Research Center of Advanced Manufacturing Technology for Fine Chemicals,Fujian Province University,Fuzhou University,Fuzhou 350116,China [4]College of Chemistry,Fuzhou University,Fuzhou 350116,China

出　　处：《Chinese Journal of Chemical Engineering》2023年第3期192-201,共10页中国化学工程学报（英文版）

基　　金：financial supported by the National Natural Science Foundation of China (22078065);Key Program of Qingyuan Innovation Laboratory (00221001);Quanzhou City Science & Technology Program of China (2020C008R)。

摘　　要：Catalytic epoxidation of alkenes is an important type of organic reaction in chemical industry,and the deep insight into catalyst deactivation will help to develop new epoxidation process.In this work,series of quaternary ammoniums bearing different cationic sizes,i.e.MTOA+(methyltrioctylammonium,[(C_(8)H_(17))_(3)CH_(3)N]+),HTMA+(hexadecyltrimethylammonium,[(C_(16)H_(33))(CH_(3))_(3)N]+) and DMDOA+(dimethyldioctadecylammonium,[(C_(18)H_(37))_(2)(CH_(3))_(2)N]+) were incorporated with polyoxometalate (POM) anions to prepare phase transfer catalysts (PTCs),which were used in the styrene epoxidations.Among them,(MTOA)_(3)PW_(4)O_(24)exhibits the best catalytic performance judged from the highest styrene conversion rate(52%) and styrene oxide selectivity (93%),during which the styrene epoxidation conditions were optimized.Meanwhile,the deactivation mechanism of this kind of PTCs was proposed firstly,i.e.in the case of low H_(2)O_(2) content,the oxidant can only be used in the styrene epoxidation,in which the catalyst can transform into stable Keggin-type POM.But when the content of H_(2)O_(2) is higher,the excess H_(2)O_(2) can reactivate the Keggin-type POM into active (PW_(4)O_(24))_(3)-anions,which can trigger the ring-opening polymerization of styrene oxide.Consequently,the catalyst is deactivated by adhered poly(styrene oxide)irreversibly,which was determined by NMR spectra.In this situation,the active moiety{PO_(4)[WO(O_(2))_(2)]_(4)}_(3)-in phase-transfer catalytic system can break into some unidentified species with low W/P ratio with the presence of epoxides.This work will be beneficial for the design of new PTCs in alkene epoxidation in fine chemical industry.

关 键 词：Phosphotungstic acid phase-transfer CATALYST Styrene epoxidation Catalyst deactivation mechanism Cation size effect 

分 类 号：O621.251[理学—有机化学]