A density-functional study of the dehydrogenation reaction of isobutane over zeolites

The dehydrogenation reaction of isobutane over zeolites was investigated at the B3LYP/6-31G** and 6-311G** levels of calculation, and with T3 and T5 c lusters representing the zeolite. The transition state (TS) exhibits a carb enium ion-like character, and the activation energy, at the best level of t heory, is 53.4 kcal/mol. Contrary to what has been previously proposed, IRC calculations show that the mechanism does not involve the formation of alk oxide, but rather the carbocation collapses directly into isobutene while t he eliminated proton, restores the zeolite's acid site. Increasing the size of the cluster and of the basis set does not change the mechanism. (C) 200 1 Elsevier Science B.V. All rights reserved.