Density Functional Theory Study of the Zeolite-Catalyzed Methylation of Benzene with Methanol
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The reaction coordinates based on Gibbs free energies for the methylation of benzene with methanol over HZSM-5 and Hβ, both concerted and stepwise pathway, were investigated by applying density functional theory. From the estimated adsorption energies of benzene and methanol on these zeolites, stronger guest–host interactions were observed in HZSM-5 compared to Hβ. We find that at low temperatures, the concerted mechanism dominates, however, the mechanism converts to the stepwise pathway at higher temperatures. The formation of methoxy group is found to be the rate-determining step for the stepwise pathway, and the calculated free energy barriers at 673 K were 138 kJ/mol for HZSM-5 and 149 kJ/mol for Hβ, lower than those in the concerted pathway (165 kJ/mol for HZSM-5 and 168 kJ/mol for Hβ), indicating that the stepwise pathway is kinetically favored for the methylation of benzene with methanol at 673 K. Gaseous methane can be produced via one intramolecular hydrogen transfer from the ring carbon to the carbon of methyl group in the protonated toluene species, and the calculated free energy barriers for forming methane over HZSM-5 and Hβ are 112 and 100 kJ/mol, respectively, suggesting that methane is more easily formed over 12-ring Hβ catalyst.
KeywordsMethylation of benzene Methanol conversion HZSM-5 Hβ DFT
This work was sponsored financially by the Natural Science Foundation of Shandong Province (ZR2018LB028).
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Conflict of interest
The authors declare that they have no conflict of interest.
- 6.Wen Z (2016) East China University of Science and Technology, Doctor ThesisGoogle Scholar
- 12.Li L, Chen R, Dai J, Sun Y, Zhang Z, Li X, Nie X, Song C, Guo X (2017) Reaction mechanism of benzene methylation with methanol over H-ZSM-5 catalyst. Acta Phys-Chim Sin 33:769–779Google Scholar
- 13.De Wispelaere K, Martínez-Espín JS, Hoffmann MJ, Svelle S, Olsbye U, Bligaard T (2018) Understanding zeolite-catalyzed benzene methylation reactions by methanol and dimethyl ether at operating conditions from first principle microkinetic modeling and experiments. Catal Today 312:35–43CrossRefGoogle Scholar
- 29.Lide DR (2009) Handbook of chemistry and physics, 90th edn. CRC Press, Boca RatonGoogle Scholar
- 31.Sun X, Hung C, Zhang J, Chen B (2009) Location of Al and acid strength of brønsted acid in beta zeolite. Acta Phys-Chim Sin 25:1136–1142Google Scholar
- 40.Wen Z, Yang D, Zhu X (2017) Alkylation of benzene and methanol and research progress of its catalysts. Mod Chem Ind 37:41–44Google Scholar