Mechanistic Insights into the Desorption of Methanol and Dimethyl ether over ZSM-5 Catalysts

Toyin Omojola, Nikolay Cherkasov, Andrew McNab, Dmitry Lukyanov, James Anderson, Evgeny Rebrov, Andre van Veen

Research output: Contribution to journalArticle

10 Citations (Scopus)
27 Downloads (Pure)

Abstract

Abstract: The desorption of methanol and dimethyl ether has been studied over fresh and hydrocarbon-occluded ZSM-5 catalysts with Si/Al ratios of 25, 36 and 135 using a temporal analysis of products reactor. The catalysts were characterized by XRD, SEM, N 2 physisorption and pyridine FT-IR. The crystal size increases with Si/Al ratio from 0.10 to 0.78 µm. The kinetic parameters were obtained using the Redhead method and a plug flow reactor model with coupled convection, adsorption and desorption steps. ZSM-5 catalysts with Si/Al ratios of 25 and 36 exhibit three adsorption sites (low, medium, and high temperature sites), while there is no difference between medium and high temperature sites at a Si/Al ratio of 135. Molecular adsorption on the low temperature site and dissociative adsorption on the medium and high temperature sites give a good match between experiment and the plug flow reactor model. The DME desorption activation energy was systematically higher than that of methanol. Adsorption stoichiometry shows that methanol and DME form clusters onto the binding sites. When non-activated re-adsorption is accounted for, a local equilibrium is reached only on the low and medium temperature binding sites. No differences were observed, other than in site densities, when extracting the kinetic parameters for fresh and activated ZSM-5 catalysts at full coverage. Graphical Abstract: [Figure not available: see fulltext.].

Original languageEnglish
Pages (from-to)474-488
Number of pages15
JournalCatalysis Letters
Volume148
Issue number1
Early online date4 Dec 2017
DOIs
Publication statusPublished - 1 Jan 2018

Keywords

  • Activation energies of desorption
  • DME
  • Methanol
  • Methanol-to-hydrocarbons
  • Polanyi–Wigner
  • Redhead
  • TPD
  • ZSM-5

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)

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