碱性X分子筛催化甲苯与甲醇侧链烷基化自由基机理研究（英文）  

Free radical mechanism investigation of the side-chain alkylation of toluene with methanol on basic zeolites X

作　　者：陈焕辉[1] 李孝慈 赵国庆[1] 谷红波[1] 朱志荣[1] 

机构地区：[1]同济大学化学系,上海200092

出　　处：《催化学报》2015年第10期1726-1732,共7页

基　　金：supported by the National Natural Science Foundation of China(51174277);Shanghai Key Basic Research(11JC1412500)~~

摘　　要：苯乙烯是重要的工业原料,年消耗量约3000万吨.传统工艺中,苯乙烯由乙苯催化脱氢得到.由于传统工艺高能耗,高污染,甲苯与甲醇侧链烷基化合成苯乙烯引起了人们广泛关注,但是目前该路线进入工业化还有很多问题需要解决,甚至催化机理仍不明确.本文对甲苯侧链烷基化机理及提高反应选择性等方面进行了研究.采用离子交换法制备CsX分子筛,在固定床反应器上进行甲苯与氘代甲醇的同位素示踪实验和硝基甲苯的侧链烷基化实验,结合量子计算明确反应机理.采用IGA-002系统测定甲醇在CsX,KX和Na X上的等温吸附线,考察甲醇在分子筛不同笼结构中的吸附情况.将氘代甲苯与甲苯在CsX,KX和活性炭催化下进行氢氘交换实验,检验自由基在不同催化剂上的稳定性.以CO2为载气进行甲苯与甲醇侧链烷基化实验,考察CO2对反应的影响.甲苯与氘代甲醇进行侧链烷基化反应时,大多数氘出现在甲苯上,仅少数氘存在于苯乙烯及乙苯上,表明甲苯氢与甲醇的甲基氘进行了氢氘交换.量子化学计算表明,甲苯与甲醇的氢氘交换沿自由基路径的能垒远小于沿离子路径的.氘代实验和量子计算结果表明,甲苯侧链烷基化过程中存在自由基,但并不能证明侧链烷基化是自由基反应.为了验证甲苯侧链烷基化反应是否为自由基机理,以4-硝基甲苯(NO2-Ph-CH3)代替甲苯与甲醇进行侧链烷基化反应.硝基是强吸电子基团,能稳定苄基负离子,如果甲苯侧链烷基化是离子反应,硝基甲苯侧链烷基化产物收率会升高.另外,硝基又能与活泼自由基生成稳定自由基,若反应为自由基机理,则硝基甲苯不发生侧链烷基化反应.分析结果表明,反应液中不存在侧链烷基化产物,确定了甲苯侧链烷基化反应为自由基机理,而不是离子机理.热力学上甲醇更容易进行生成CO和H2等的副反应,从而减少CH·3与H·碰撞甲醇的几率.甲醇等�The side-chain alkylation of toluene represents a novel, environmentally friendly, and low cost route for the production of styrene. However, the yield of styrene produced in this way is cur-rently low, and the mechanism responsible for the side-chain alkylation of toluene is poorly un-derstood. Furthermore, the reason for the higher catalytic efficiency of CsX over NaX and KX remains unclear. In this work, the free radical mechanism of the side-chain alkylation of toluene over basic zeolite X has been elucidated using quantum chemical calculations, together with isotope tracing experiments and the reaction betweenp-nitrotoluene and methanol. The adsorp-tion isotherm of methanol showed that Cs＋ ions could block methanol from accessing theβ-cage, which is where the side-chain alkylation reaction occurred. Furthermore, the H–D exchange results between toluene and deuterated toluene （C6D5CD3） showed that CsX was more efficient as a catalyst than KX for the conversion of toluene to the corresponding benzyl radical （C6H5CH2？）. These two results therefore explain the higher catalytic activity of CsX towards side-chain alkyla-tion than KX. Based on the free radical mechanism, the selectivity of styrene could be increased from 17.4% to 59.4% using CO2 as carrier gas instead of N2.

关 键 词：甲苯 侧链烷基化 自由基机理 X分子筛 苯乙烯 同位素示踪 

分 类 号：O643.31[理学—物理化学] TQ241.21[理学—化学]