Acidity and cracking activity changes during coke deactivation of ultrastable Y zeolite

P. D. Hopkins, J. T. Miller, B. L. Meyers, G. J. Ray, R. T. Roginski, M. A. Kuehne, H. H. Kung

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Abstract

Changes in acidic ultrastable Y zeolite (H-USY) due to coke deactivation during hexane cracking were determined by ammonia TPD, microcalorimetry, IR spectroscopy of adsorbed pyridine, 13C NMR, powder XRD, TGA of hexane adsorption, and nitrogen and argon adsorption. Small amounts of coke produced a large decrease in activity; however, few acid sites were poisoned. Compared to a fresh USY zeolite, coke deactivated H-USY did not show significant changes in the acid strength distribution, number of acid sites, fraction of Brønsted and Lewis acid sites, pore size distribution, or hexane diffusivity that could account for the large decrease in the cracking activity. It is proposed that the rapid loss in activity resulting from a small decrease in the number of acid sites is consistent with a site poisoning deactivation model for a diffusion-limited reaction, i.e., the rate of hexane reaction is greater than the rate of diffusion. For a diffusion limited reaction, the initial hexane cracking and coke deposition occurs primarily at active sites near the external surface of the crystal with little reaction at the particle interior. As deactivation proceeds, the thickness of coked region grows and hexane diffuses further into the zeolite particle before reaction.

Original languageEnglish
Pages (from-to)29-48
Number of pages20
JournalApplied Catalysis A: General
Volume136
Issue number1
DOIs
Publication statusPublished - Feb 29 1996

Keywords

  • Acid sites in USY
  • Coke deactivation
  • Deactivation of USY
  • Hexane cracking on USY
  • IR
  • Microcalorimetry
  • TPD
  • USY zeolite

ASJC Scopus subject areas

  • Catalysis
  • Process Chemistry and Technology

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    Hopkins, P. D., Miller, J. T., Meyers, B. L., Ray, G. J., Roginski, R. T., Kuehne, M. A., & Kung, H. H. (1996). Acidity and cracking activity changes during coke deactivation of ultrastable Y zeolite. Applied Catalysis A: General, 136(1), 29-48. https://doi.org/10.1016/0926-860X(95)00246-4