Acta Phys. -Chim. Sin. ›› 2013, Vol. 29 ›› Issue (07): 1467-1478.doi: 10.3866/PKU.WHXB201304262

• THEORETICAL AND COMPUTATIONAL CHEMISTRY • Previous Articles     Next Articles

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.

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