The roles of acid strength and pore diffusion in the enhanced cracking activity of steamed Y zeolites

B. A. Williams, S. M. Babitz, J. T. Miller, R. Q. Snurr, Harold H Kung

Research output: Contribution to journalArticle

138 Citations (Scopus)

Abstract

Steamed HY or ultrastable Y (H-USY) zeolites are active hydrocarbon cracking catalysts. The high activity of H-USY compared to HY zeolite has been previously explained by the generation of unusually strong and active Brønsted acid sites, or an increase in the number of accessible sites in a micropore diffusion-controlled reaction. However, neither model explains the accumulated literature observations. A model is proposed that incorporates a change in the predominant cracking reaction mechanism as a function of alkane conversion and the very different rates of these mechanisms. Additionally, an oligomeric cracking mechanism is introduced to explicitly account for coking and deactivation of the catalyst. The model is capable of accounting for most literature results. It concludes that the large enhancement in cracking activity by steaming is due to a proportionally smaller increase in external surface area of the zeolite crystals and possibly a small increase in the specific initiation activity of each site. These small changes lead to a much larger overall effect because of the sensitive dependence of oligomeric cracking and, to a lesser extent, bimolecular cracking on the alkene partial pressure.

Original languageEnglish
Pages (from-to)161-175
Number of pages15
JournalApplied Catalysis A: General
Volume177
Issue number2
Publication statusPublished - Feb 22 1999

Fingerprint

Zeolites
Acids
Catalysts
Alkanes
Coking
Alkenes
Hydrocarbons
Partial pressure
Paraffins
Olefins
Crystals

Keywords

  • Cracking mechanism on zeolites
  • Cracking, effect of acid strength
  • Cracking, effect of diffusion
  • Cracking, effect of steaming
  • Diffusion effect on cracking
  • Hydrocarbon cracking
  • Zeolite Y

ASJC Scopus subject areas

  • Catalysis
  • Process Chemistry and Technology

Cite this

The roles of acid strength and pore diffusion in the enhanced cracking activity of steamed Y zeolites. / Williams, B. A.; Babitz, S. M.; Miller, J. T.; Snurr, R. Q.; Kung, Harold H.

In: Applied Catalysis A: General, Vol. 177, No. 2, 22.02.1999, p. 161-175.

Research output: Contribution to journalArticle

Williams, B. A. ; Babitz, S. M. ; Miller, J. T. ; Snurr, R. Q. ; Kung, Harold H. / The roles of acid strength and pore diffusion in the enhanced cracking activity of steamed Y zeolites. In: Applied Catalysis A: General. 1999 ; Vol. 177, No. 2. pp. 161-175.
@article{16990b997b4f4ead82b53d30f0e11a98,
title = "The roles of acid strength and pore diffusion in the enhanced cracking activity of steamed Y zeolites",
abstract = "Steamed HY or ultrastable Y (H-USY) zeolites are active hydrocarbon cracking catalysts. The high activity of H-USY compared to HY zeolite has been previously explained by the generation of unusually strong and active Br{\o}nsted acid sites, or an increase in the number of accessible sites in a micropore diffusion-controlled reaction. However, neither model explains the accumulated literature observations. A model is proposed that incorporates a change in the predominant cracking reaction mechanism as a function of alkane conversion and the very different rates of these mechanisms. Additionally, an oligomeric cracking mechanism is introduced to explicitly account for coking and deactivation of the catalyst. The model is capable of accounting for most literature results. It concludes that the large enhancement in cracking activity by steaming is due to a proportionally smaller increase in external surface area of the zeolite crystals and possibly a small increase in the specific initiation activity of each site. These small changes lead to a much larger overall effect because of the sensitive dependence of oligomeric cracking and, to a lesser extent, bimolecular cracking on the alkene partial pressure.",
keywords = "Cracking mechanism on zeolites, Cracking, effect of acid strength, Cracking, effect of diffusion, Cracking, effect of steaming, Diffusion effect on cracking, Hydrocarbon cracking, Zeolite Y",
author = "Williams, {B. A.} and Babitz, {S. M.} and Miller, {J. T.} and Snurr, {R. Q.} and Kung, {Harold H}",
year = "1999",
month = "2",
day = "22",
language = "English",
volume = "177",
pages = "161--175",
journal = "Applied Catalysis A: General",
issn = "0926-860X",
publisher = "Elsevier",
number = "2",

}

TY - JOUR

T1 - The roles of acid strength and pore diffusion in the enhanced cracking activity of steamed Y zeolites

AU - Williams, B. A.

AU - Babitz, S. M.

AU - Miller, J. T.

AU - Snurr, R. Q.

AU - Kung, Harold H

PY - 1999/2/22

Y1 - 1999/2/22

N2 - Steamed HY or ultrastable Y (H-USY) zeolites are active hydrocarbon cracking catalysts. The high activity of H-USY compared to HY zeolite has been previously explained by the generation of unusually strong and active Brønsted acid sites, or an increase in the number of accessible sites in a micropore diffusion-controlled reaction. However, neither model explains the accumulated literature observations. A model is proposed that incorporates a change in the predominant cracking reaction mechanism as a function of alkane conversion and the very different rates of these mechanisms. Additionally, an oligomeric cracking mechanism is introduced to explicitly account for coking and deactivation of the catalyst. The model is capable of accounting for most literature results. It concludes that the large enhancement in cracking activity by steaming is due to a proportionally smaller increase in external surface area of the zeolite crystals and possibly a small increase in the specific initiation activity of each site. These small changes lead to a much larger overall effect because of the sensitive dependence of oligomeric cracking and, to a lesser extent, bimolecular cracking on the alkene partial pressure.

AB - Steamed HY or ultrastable Y (H-USY) zeolites are active hydrocarbon cracking catalysts. The high activity of H-USY compared to HY zeolite has been previously explained by the generation of unusually strong and active Brønsted acid sites, or an increase in the number of accessible sites in a micropore diffusion-controlled reaction. However, neither model explains the accumulated literature observations. A model is proposed that incorporates a change in the predominant cracking reaction mechanism as a function of alkane conversion and the very different rates of these mechanisms. Additionally, an oligomeric cracking mechanism is introduced to explicitly account for coking and deactivation of the catalyst. The model is capable of accounting for most literature results. It concludes that the large enhancement in cracking activity by steaming is due to a proportionally smaller increase in external surface area of the zeolite crystals and possibly a small increase in the specific initiation activity of each site. These small changes lead to a much larger overall effect because of the sensitive dependence of oligomeric cracking and, to a lesser extent, bimolecular cracking on the alkene partial pressure.

KW - Cracking mechanism on zeolites

KW - Cracking, effect of acid strength

KW - Cracking, effect of diffusion

KW - Cracking, effect of steaming

KW - Diffusion effect on cracking

KW - Hydrocarbon cracking

KW - Zeolite Y

UR - http://www.scopus.com/inward/record.url?scp=0040887840&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0040887840&partnerID=8YFLogxK

M3 - Article

VL - 177

SP - 161

EP - 175

JO - Applied Catalysis A: General

JF - Applied Catalysis A: General

SN - 0926-860X

IS - 2

ER -