A two-layer ONIOM study of thiophene cracking catalyzed by proton-and cation-exchanged FAU zeolite

作者：Sun, Yingxin^*; Mao, Xinfeng; Pei, Supeng^*

来源：Journal of Molecular Modeling, 2016, 22(2): 51.

DOI：10.1007/s00894-016-2916-1

• Thiophene
• Hydrodesulfurization mechanism
• Cation-exchanged FAU zeolite
• C-S bond cracking
• Bimolecular desulfurization step

A two-layer ONIOM study on the hydrodesulfurization mechanism of thiophene in H-FAU and M-FAU (M = Li+, Na+, and K+) has been carried out. The calculated results reveal that in H-FAU, for a unimolecular mechanism, the rate-determining step is hydrogenation of alkoxide intermediate. The assistance of H2O and H2S molecules does not reduce the difficulty of the C-S bond cracking step more effectively. A bimolecular hydrodesulfurization mechanism is more favorable due to the lower activation barriers. The rate-determining step is the formation of 2-methylthiophene, not the C-S bond cracking of thiophene. Moreover, the ring opening of thiophene is much easier to occur than the desulfurization step. A careful analysis of energetics indicates that H2S, propene, and methyl thiophene are the major products for the hydrodesulfurization process of thiophene over H-FAU zeolite, in good agreement with experimental findings. In M-FAU zeolites, both unimolecular and bimolecular cracking processes are difficult to occur because of the high energy barriers. Compared to the case on H-FAU, the metal cations on M-FAU increase the difficulty of occurrence of bimolecular polymerization and subsequent C-S bond cracking steps.

• 出版日期2016-2
• 单位上海应用技术大学