Conversion of methanol to hydrocarbons over zeolite H-ZSM-5: On the origin of the olefinic species

This study examined the reaction mechanism with respect to both catalyst deactivation and product formation in the conversion of methanol to hydrocarbons over zeolite H-ZSM-5. The reactivity of the organics residing in the zeolite voids during the reaction was assessed by transient 12C/ 13C methanol...

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Bibliographic Details
Published in:Journal of catalysis 2007-07, Vol.249 (2), p.195-207
Main Authors: Bjørgen, Morten, Svelle, Stian, Joensen, Finn, Nerlov, Jesper, Kolboe, Stein, Bonino, Francesca, Palumbo, Luisa, Bordiga, Silvia, Olsbye, Unni
Format: Article
Language:English
Subjects:
Catalysis
Catalysts
Catalytic cracking
Chemistry
Coking
Deactivation
Exact sciences and technology
General and physical chemistry
Hydrocarbon pool
Hydrocarbons
Ion-exchange
Mechanism
Methanol
MFI
MTG
MTH
MTO
Polyolefins
Surface physical chemistry
Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry
Zeolite
Zeolites: preparations and properties
ZSM-5
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Summary:This study examined the reaction mechanism with respect to both catalyst deactivation and product formation in the conversion of methanol to hydrocarbons over zeolite H-ZSM-5. The reactivity of the organics residing in the zeolite voids during the reaction was assessed by transient 12C/ 13C methanol-switching experiments. In contrast to previously investigated catalysts (H-SAPO-34 and H-beta), hexamethylbenzene is virtually unreactive in H-ZSM-5 and is thus not a relevant reaction intermediate for alkene formation. However, the lower methylbenzenes are reaction intermediates in a hydrocarbon pool-type mechanistic cycle and are responsible for the formation of ethene and propene. An additional reaction cycle not applicable for ethene also must be taken into account. The C 3+ alkenes are to formed through rapid alkene methylation and cracking steps to a considerable extent; thus, methanol is converted to hydrocarbons according to two catalytic cycles over H-ZSM-5. Moreover, in contrast to what occurs for large-pore zeolites/zeotypes, molecules larger than hexamethylbenzenes are not built up inside the H-ZSM-5 channels during deactivation. Thus, deactivation is explained by coke formation on the external surface of the zeolite crystallites only. This is a plausible rationale for the superior lifetime properties of H-ZSM-5 in the methanol-to-hydrocarbon reaction.
ISSN:0021-9517
1090-2694
DOI:10.1016/j.jcat.2007.04.006