物理化学学报 >> 2013, Vol. 29 >> Issue (07): 1467-1478.doi: 10.3866/PKU.WHXB201304262

理论与计算化学 上一篇    下一篇

H-ZSM-5催化甲苯与碳酸二甲酯和甲醇甲基化的反应机理

李玲玲1, Janik J. Michael2,3, 聂小娃1,4, 宋春山1,2,3, 郭新闻1   

  1. 1 大连理工大学化工学院精细化工国家重点实验室, PSU-DUT联合能源研究中心, 辽宁 大连 116024;
    2 宾夕法尼亚州立大学能源与矿物工程系能源研究所, PSU-DUT联合能源研究中心, 宾夕法尼亚 16802, 美国;
    3 宾夕法尼亚州立大学化学工程系, 宾夕法尼亚 16802, 美国;
    4 俄亥俄州立大学化工与生物分子工程系, 俄亥俄 43210, 美国
  • 收稿日期:2013-01-29 修回日期:2013-04-26 发布日期:2013-06-14
  • 通讯作者: Janik J. Michael, 郭新闻 E-mail:mjanik@engr.psu.edu;guoxw@dlut.edu.cn
  • 基金资助:

    新世纪优秀人才项目(NCET-04-0268)及教育部111 计划工程基金和大连理工大学网络与信息化中心高性能计算部基金资助

Reaction Mechanism of Toluene Methylation with Dimethyl Carbonate or Methanol Catalyzed by H-ZSM-5

LI Ling-Ling1, Janik J. Michael2,3, NIE Xiao-Wa1,4, SONG Chun-Shan1,2,3, GUO Xin-Wen1   

  1. 1 State Key Laboratory of Fine Chemicals, PSU-DUT Joint Center for Energy Research, School of Chemical Engineering, Dalian University of Technology, Dalian 116024, Liaoning Province, P. R. China;
    2 EMS Energy Institute, PSU-DUT Joint Center for Energy Research and Department of Energy & Mineral Engineering, Pennsylvania State University, University Park, PA 16802, USA;
    3 Department of Chemical Engineering, Pennsylvania State University, University Park, PA 16802, USA;
    4 Department of Chemical & Biomolecular Engineering, The Ohio State University, Columbus, OH 43210, USA
  • Received:2013-01-29 Revised:2013-04-26 Published:2013-06-14
  • Contact: Janik J. Michael, GUO Xin-Wen E-mail:mjanik@engr.psu.edu;guoxw@dlut.edu.cn
  • Supported by:

    The project was supported by the Program for New Century Excellent Talent in University, China (NCET-04-0268), Plan 111 Project of the Ministry of Education of China, and High Performance Computing Department of Network and Information Center, Dalian University of Technology, China.

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摘要：

对二甲苯是重要的石油化工产品之一, 可以通过甲苯甲基化生产. 本文采用“our own-N-layeredintegrated molecular orbital+molecular mechanics”(ONIOM)和密度泛函理论(DFT)结合的方法, 计算了H-ZSM-5催化甲苯与碳酸二甲酯(DMC)和甲醇甲基化反应机理. 考察了反应物吸附和产物脱附. 描述了主要的中间物种和过渡态的结构. 用计算的速率常数来估计甲苯甲基化反应的动力学活性. H-ZSM-5 催化的甲苯与DMC和甲醇甲基化的机理不同. 甲苯和DMC甲基化包括DMC完全解离, 接着甲基化生成二甲苯异构体. 相比而言, 在甲苯甲基化反应中, 甲醇作为甲基化试剂的活性比DMC更好. 甲苯和甲醇甲基化的分步反应路径和联合反应路径的本征活化能相似. 在773 K, 分步反应路径的速率常数比联合反应路径更高. 在甲苯和这两种试剂甲基化的反应中, 生成对二甲苯为动力学优先, 而间二甲苯为能量最低产物. 我们的计算结果和实验观察到的现象一致.

关键词: 密度泛函理论, ONIOM, 甲苯甲基化, 碳酸二甲酯, 甲醇, H-ZSM-5

Abstract:

Para-xylene is an important petrochemical that can be produced by the methylation of toluene. Here, the mechanism of toluene methylation with dimethyl carbonate (DMC) or methanol catalyzed by H-ZSM-5 was studied using the“our own N-layered integrated molecular orbital+molecular mechanics” (ONIOM) in combination with density functional theory (DFT) methods. The adsorption of reactants and desorption of products are considered, and the structures of important intermediates and transition states are described. Computational rate constants are used to estimate the kinetic activity of toluene methylation reactions. The reaction mechanism of toluene methylation with DMC and that with methanol catalyzed by H-ZSM-5 differ. Toluene methylation with DMC involves full decomposition of DMC prior to methylation to form xylene isomers. In contrast, methanol is more active than DMC as the methylation reagent in toluene methylation. The stepwise and concerted paths of toluene methylation with methanol have similar intrinsic activation energies. At 773 K, the stepwise path has a higher rate constant than the concerted one. For toluene methylation with both reagents, para-xylene formation is kinetically preferred, whereas meta-xylene is the lowest-energy product. The results of our calculations agree well with experimental observations.

Key words: Density functional theory, ONIOM, Toluene methylation, Dimethyl carbonate, Methanol, H-ZSM-5

MSC2000: 

  • O641