Journal
JOURNAL OF CATALYSIS
Volume 285, Issue 1, Pages 115-123Publisher
ACADEMIC PRESS INC ELSEVIER SCIENCE
DOI: 10.1016/j.jcat.2011.09.018
Keywords
Methanol-to-gasoline conversion; Zeolites; Shape selectivity; Hydrocarbon pool; Surface methoxide groups; Alkylation; Olefin methylation; Bronsted acid catalysis
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Funding
- Abu Dhabi-Minnesota Institute for Research Excellence (ADMIRE)
- Petroleum Institute of Abu Dhabi
- Department of Chemical Engineering and Materials Science of the University of Minnesota
- American Chemical Society [ACS PRF DNI5 49591]
- National Science Foundation [CBET 1055846]
- Directorate For Engineering [1055846] Funding Source: National Science Foundation
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Ethylene and propylene methylation rates increased linearly with olefin pressure but did not depend on dimethyl ether (DME) pressures on proton-form FER, MFI, MOR, and BEA zeolites at low conversions (<0.2%) and high DME/olefin ratios (30:1) in accordance with a mechanism that involves the zeolite surface being predominantly covered by DME-derived species reacting with olefins. Higher first-order reaction rate constants for both ethylene and propylene methylation were observed over H-BEA and H-MFI compared with H-FER and H-MOR, indicating that olefin methylation reaction cycles involved in the conversion of methanol-to-gasoline over zeolitic acids are propagated to varying extents by different framework materials. Systematically lower activation barriers and higher rate constants were observed for propylene methylation in comparison with ethylene methylation over all frameworks studied, reflecting the increased stability of reaction intermediates and activated complexes with increasing olefin substitution. A binomial distribution of d(0)/d(3)/d(6) in unreacted DME upon introduction of equimolar protium- and deuterium-form DME under steady-state reaction conditions of ethylene methylation over H-MFI suggests the presence and facile formation of reactive surface-bound methoxide species and the absence of C-H bond cleavage. (C) 2011 Elsevier Inc. All rights reserved.
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