Isobutane Cracking over Y-Zeolites: II. Catalytic Cycles and Reaction Selectivity

We describe the activity and selectivity of isobutane cracking on Y-zeolite-based catalysts in terms of catalytic cycles composed of initiation, β-scission, oligomerization, olefin desorption, isomerization, and hydride ion transfer reactions involving carbenium ions. Olefin desorption and isomeriza...

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Bibliographic Details
Published inJournal of catalysis Vol. 153; no. 1; pp. 65 - 75
Main Authors Yaluris, G., Rekoske, J.E., Aparicio, L.M., Madon, R.J., Dumesic, J.A.
Format Journal Article
LanguageEnglish
Published Amsterdam Elsevier Inc 15.04.1995
Elsevier
Subjects
Applied sciences
Energy
Exact sciences and technology
Fuel processing. Carbochemistry and petrochemistry
Fuels
Gas processing
Catalyst selectivity
Reaction mechanism
Fluid catalytic cracking
Kinetics
Zeolite
Isobutane
Catalyst activity
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Summary:We describe the activity and selectivity of isobutane cracking on Y-zeolite-based catalysts in terms of catalytic cycles composed of initiation, β-scission, oligomerization, olefin desorption, isomerization, and hydride ion transfer reactions involving carbenium ions. Olefin desorption and isomerization reactions are at quasi-equilibrium, with the former reactions determining the surface carbenium ion coverages. Microcalorimetric measurements of ammonia adsorption show that catalyst steaming leads to a decrease in the number and strength of acid sites. Decreasing the strength of Brønsted acid sites results in decreasing surface carbenium ion coverages and decreasing rates of all reactions. The hydride ion transfer cycles are affected most by catalyst steaming, leading to lower paraffin selectivities. Lower temperatures and higher conversions increase carbenium ion coverages and favor hydride ion transfer cycles, leading to higher paraffin selectivities.
ISSN:0021-9517
1090-2694
DOI:10.1006/jcat.1995.1108