催化学报

催化学报 ›› 2010, Vol. 31 ›› Issue (6): 645-650.

• 研究论文 • 上一篇    下一篇

HZSM-5 分子筛上乙烯芳构化过程中 C4 至 C6 中间体的反应机理

曹亮 1, 周丹红 1, 邢双英 1, 李新 2   

  1. 1 辽宁师范大学化学化工学院功能材料化学研究所, 辽宁大连 1160292 中国科学院大连化学物理研究所催化基础国家重点实验室, 辽宁大连 116023
  • 收稿日期:2010-06-25 出版日期:2010-06-25 发布日期:2013-12-05

Reaction Mechanism of Ethylene Aromatization over HZSM-5 Zeolite: From C4 to C6 Intermediates

CAO Liang1, ZHOU Danhong1,*, XING Shuangying1, LI Xin2   

  1. 1Institute of Chemistry for Functionalized Materials, College of Chemistry and Chemical Engineering, Liaoning Normal University, Dalian 116029, Liaoning, China2State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, Liaoning, China
  • Received:2010-06-25 Online:2010-06-25 Published:2013-12-05

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被引次数

4

摘要： 应用量子力学和分子力学联合的 ONIOM2 (B3LYP/6-31G(d,p):UFF) 方法, 采用包含分子筛孔道结构的 78T 簇模型, 对 HZSM-5 分子筛上乙烯芳构化过程中 C4 至 C6 中间体的反应历程进行了研究, 探讨了分子筛的酸催化机理和择形催化作用. 结果表明, 作为乙烯二聚产物的表面正丁基烷氧络合物 (C4) 直接与乙烯作用得到正己基烷氧络合物 (C6), 在分子筛孔穴尺寸的限制下, 很难实现碳链的折叠环化. 按照间歇反应历程, 丁基烷氧络合物先发生 C–O 键断裂, 脱质子生成 1-丁烯, 然后在酸性位上再与乙烯加成, 在分子筛表面生成 3-甲基戊基烷氧络合物. 该烷氧络合物脱除质子给分子筛, 同时环化生成甲基环戊烷, 后者再与分子筛酸性质子共同脱除氢分子, 生成不稳定的碳正离子中间体, 然后重构成环己烷正离子. 丁基烷氧络合物脱质子的活化能为 158.42 kJ/mol; 1-丁烯与乙烯加成反应的活化能为 130.71 kJ/mol; 3-甲基戊基烷氧络合物脱氢环化生成甲基环戊烷的活化能为 122.06 kJ/mol. 由于孔穴的限域作用, 五员环的甲基环戊烷是重要的中间体.

关键词: 密度泛函理论, 乙烯, 芳构化, HZSM-5 分子筛, 反应机理, 禁闭效应

Abstract: The ONIOM2 (B3LYP/6-31G(d,p):UFF) method based on the 78T cluster model was used to study the reaction mechanism of C4 to C6 intermediates during the ethylene aromatization over HZSM-5 zeolite. The catalytic mechanism of acidic zeolite and the effect of zeolite pore size on the shape selectivity for the products was discussed. The results indicated that the n-butoxide, which is the intermediate product of ethylene dimmerization, reacted with ethylene to form n-hexane alkoxide, but it was difficult to carry out further cyclization because of the restriction of the pore size of ZSM-5 zeolite. However, along the stepwise pathways, n-butoxide was transformed into n-butene through deprontonation and then reacted with ethylene to form 3-methylpentane alkoxide intermediate, which then formed methylcyclopentane through cyclization and deprotonation. The methylcyclopentane released a hydrogen molecule by the aid of zeolite acidic proton and formed the unstable methyl-cyclopentane carbonium, which then generated the cyclohexane carbonium through reconfiguration. The calculated activation energy was 158.42 kJ/mol for n-butoxide deprontonation, 130.71 kJ/mol for the oligomerization of 1-butene and ethylene, and 122.06 kJ/mol for the cyclization of 3-methylpentane alkoxide. As a result of the confinement of zeolite pore, the five-member ringed me-thylcyclopentane was formed as a crucial intermediate.

Key words: density functional theory, ethylene, aromatization, HZSM-5 zeolite, reaction mechanism, confinement effect