Reaction kinetic behavior of sulfated-zirconia catalysts for butane isomerization

Citation
Z. Hong et al., Reaction kinetic behavior of sulfated-zirconia catalysts for butane isomerization, CATAL TODAY, 51(2), 1999, pp. 269-288
Citations number
110
Categorie Soggetti
Physical Chemistry/Chemical Physics
Journal title
CATALYSIS TODAY
ISSN journal
09205861 → ACNP
Volume
51
Issue
2
Year of publication
1999
Pages
269 - 288
Database
ISI
SICI code
0920-5861(19990630)51:2<269:RKBOSC>2.0.ZU;2-Z
Abstract
Sulfated-zirconia catalysts show rapid deactivation (deactivation constants near 0.02 min(-1)) during isomerization of n-butane when olefins are prese nt in the feed. Removal of olefins from the feed decreases the rate of cata lyst deactivation over sulfated-zirconia (to values near 0.007 min(-1)). Th e rates of deactivation are slower during isobutane isomerization (deactiva tion constants near 0.003 min(-1)) than during n-butane isomerization over sulfated-zirconia catalysts in the presence of feed olefins. Deactivation o f the catalysts during n-butane isomerization appears to be caused by the p roduction of coke on the catalyst from straight-chain olefinic species eith er present in the feed or produced on the catalyst under reaction condition s. Butane isomerization over sulfated-zirconia can be viewed as being a sur face chain reaction comprising initiation, propagation, and termination ste ps. The primary initiation step in the absence of feed olefins is the dehyd rogenation of butane over sulfated-zirconia, generating butenes which adsor b onto acid sites. Quantum-chemical calculations, employing density functio nal theory, suggest that the dissociative adsorption of dihydrogen, isobuty lene hydrogenation, and dissociative adsorption of isobutane are feasible o ver the sulfated-zirconia cluster, and these reactions take place over the Zr-O sites. (C) 1999 Elsevier Science B.V. All rights reserved.