Kinetic evaluation of deactivation pathways in methanol-to-hydrocarbon catalysis on HZSM-5 with formaldehyde, olefinic, dieneic, and aromatic Co-Feeds

Brandon L. Foley, Blake A. Johnson, Aditya Bhan

Research output: Contribution to journalArticlepeer-review

25 Scopus citations

Abstract

Formaldehyde (HCHO), formed in situ by transfer dehydrogenation of methanol in methanol-to-hydrocarbon (MTH) conversion, reacts with other organic species including olefins, dienes, and aromatics to cause deactivation. The propensity of these formaldehyde-mediated pathways to cause deactivation during MTH catalysis is evaluated using site-loss selectivity and yield as numerical assessors of catalyst deactivation. The site-loss selectivity of HCHO with 0.2 kPa HCHO and 12 kPa CH3OH at 673 K decreases by 80% when co-feeding 1 kPa propylene, increases by 2× when co-feeding toluene, and increases by 150× when co-feeding 1,3-butadiene, suggesting that olefins react with HCHO in nondeactivating pathways, while aromatics and dienes react with HCHO in pathways that lead to deactivation. Further, dienes have a much higher propensity than aromatics to cause deactivation via HCHO-mediated reactions when compared on a molar basis, suggesting that dienes may be critical intermediates in HCHO-mediated deactivation pathways. This is corroborated by evidence that the site-loss selectivity of HCHO increases with increasing HCHO co-feed pressure, implying that prevalent deactivation pathways are higher order in HCHO than predominant competing nondeactivation pathways. Plausibly this occurs because HCHO reacts with itself or with a HCHO-derived species en route to deactivation, such as a diene or an aromatic, which are known products of HCHO-mediated pathways during MTH catalysis. Therefore, dienes along with HCHO should be considered as critical intermediates in fomenting deactivation in MTH catalysis and strategies to eliminate polyunsaturated species and/or intercept reaction sequences of these intermediates with HCHO will likely enhance catalyst lifetime during MTH catalysis.

Original languageEnglish (US)
Pages (from-to)3628-3637
Number of pages10
JournalACS Catalysis
Volume11
Issue number6
DOIs
StatePublished - Mar 8 2021

Bibliographical note

Publisher Copyright:
© 2021 American Chemical Society

Keywords

  • Butadiene
  • Chemical transients
  • Deactivation
  • Formaldehyde
  • Methanol-to-hydrocarbon conversion

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