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.
|Original language||English (US)|
|Number of pages||9|
|Journal||Journal of Catalysis|
|State||Published - Jan 2012|
Bibliographical noteFunding Information:
This work was supported by the Abu Dhabi-Minnesota Institute for Research Excellence (ADMIRE); a partnership between the Petroleum Institute of Abu Dhabi and the Department of Chemical Engineering and Materials Science of the University of Minnesota. Acknowledgement is also made to the donors of the American Chemical Society Petroleum Research Fund for partial support of this research (ACS PRF DNI5 49591) and the National Science Foundation (CBET 1055846). The authors would also like to thank Joel Fawaz and Yong Sam Ng for their contributions to the reaction studies presented herein.
- Brønsted acid catalysis
- Hydrocarbon pool
- Methanol-to-gasoline conversion
- Olefin methylation
- Shape selectivity
- Surface methoxide groups