Acta Phys. -Chim. Sin. ›› 2017, Vol. 33 ›› Issue (4): 769-779.doi: 10.3866/PKU.WHXB201612162

• ARTICLE • Previous Articles     Next Articles

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)

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