Kinetics and mechanism of olefin methylation reactions on zeolites

Ian M. Hill, Saleh Al Hashimi, Aditya Bhan

Research output: Contribution to journalArticlepeer-review

70 Scopus citations

Abstract

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 languageEnglish (US)
Pages (from-to)115-123
Number of pages9
JournalJournal of Catalysis
Volume285
Issue number1
DOIs
StatePublished - Jan 1 2012

Keywords

  • Alkylation
  • Brønsted acid catalysis
  • Hydrocarbon pool
  • Methanol-to-gasoline conversion
  • Olefin methylation
  • Shape selectivity
  • Surface methoxide groups
  • Zeolites

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