物理化学学报 >> 2017, Vol. 33 >> Issue (4): 769-779.doi: 10.3866/PKU.WHXB201612162

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苯和甲醇在H-ZSM-5催化剂上甲基化的反应机理

李玲玲1,陈韧1,戴戬1,孙野1,张作良1,李晓亮1,聂小娃2,*(),宋春山2,3,郭新闻2,*()   

  1. 1 辽宁科技学院冶金工程学院,辽宁本溪117004
    2 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
    3 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,大学城16802,宾夕法尼亚,美国
  • 收稿日期:2016-10-31 发布日期:2017-03-23
  • 通讯作者: 聂小娃,郭新闻 E-mail:niexiaowa@dlut.edu.cn;guoxw@dlut.edu.cn
  • 基金资助:
    辽宁省教育厅科学研究一般项目基金(L2014503);辽宁省自然科学基金项目(201602403);辽宁科技学院博士科研启动基金项目(1406B08);国家自然科学基金项目(21503027)

Reaction Mechanism of Benzene Methylation with Methanol over H-ZSM-5 Catalyst

Ling-Ling LI1,Ren CHEN1,Jian DAI1,Ye SUN1,Zuo-Liang ZHANG1,Xiao-Liang LI1,Xiao-Wa NIE2,*(),Chun-Shan SONG2,3,Xin-Wen GUO2,*()   

  1. 1 Department of Metallurgical Engineering, Liaoning Institute of Science and Technology, Benxi 117004, Liaoning Province, P. R. China
    2 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
    3 EMS Energy Institute, PSU-DUT Joint Center for Energy Research and Department of Energy & Mineral Engineering, Pennsylvania State University, University Park, PA 16802, USA
  • Received:2016-10-31 Published:2017-03-23
  • Contact: Xiao-Wa NIE,Xin-Wen GUO E-mail:niexiaowa@dlut.edu.cn;guoxw@dlut.edu.cn
  • Supported by:
    the Scientific Research Foundation for the general Program of Department of Education of Liaoning Province of China(L2014503);Natural Science Foundation of Liaoning Province, China(201602403);Research Fund for the Doctoral Program of Liaoning Institute of Science and Technology, China(1406B08);National Natural Science Foundation of China(21503027)

摘要:

采用“our own-N-layered integrated molecular orbital + molecular mechanics”(ONIOM)和密度泛函理论(DFT)结合的方法,在5T、12T、104T9和104T12 H-ZSM-5模型中研究了苯和甲醇甲基化的分步和协同机理。描述了中间体物种和过渡态的结构。考察了H-ZSM-5催化剂Br?nsted(B)酸强度对苯和甲醇甲基化反应机理的影响。反应活化能结果表明,在B酸强度更强的H-ZSM-5催化剂上,苯和甲醇甲基化反应更容易发生,反应活化能更低。随着B酸强度增强,分步机理的反应活化能比协同机理的反应活化能降低的更多。B酸强度增强对分步机理更有利。当分步机理成为主导反应路径时,分步机理中甲醇脱水步骤生成的甲氧基中间体进一步生成大体积烃类的副反应会导致H-ZSM-5催化剂因积炭而失活。合理调变H-ZSM-5催化剂的酸强度对提高催化剂的催化活性和稳定性有重要意义。

关键词: 密度泛函理论, ONIOM, 苯甲基化, 甲醇, H-ZSM-5

Abstract:

The stepwise and concerted mechanisms of benzene methylation with methanol were studied with the 5T, 12T, 104T9, and 104T12 H-ZSM-5 models using the"our own-N-layered integrated molecular orbital + molecular mechanics"(ONIOM) in combination with density functional theory (DFT) methods. The structures of intermediate species and transition states were described. The effect of the Br?nsted (B) acid strength of HZSM-5 catalyst on the reaction mechanism of benzene methylation with methanol was considered. The reaction activation energy results indicate that benzene methylation with methanol preferentially occurs over H-ZSM-5 catalyst with greater B acid strength, and a lowering of the activation barrier was observed. With increasing B acid strength, the reaction activation energy of the stepwise mechanism decreases more than that of the concerted mechanism. Increasing the B acidic strength is more beneficial to the stepwise mechanism. When the stepwise mechanism becomes the dominant reaction path, the secondary reaction arising from further formation of bulky hydrocarbons through the methoxide intermediate produced in the methanol dehydration step of the stepwise mechanism might lead to the inactivation of the H-ZSM-5 catalyst owing to coke formation. Reasonable modulation the acid strength of the H-ZSM-5 catalyst is important in improving its catalytic activity and stability of the catalyst.

Key words: Density functional theory, ONIOM, Benzene methylation, Methanol, H-ZSM-5

MSC2000: 

  • O641