MECHANISMS OF HEPTANE ISOMERIZATION ON BIFUNCTIONAL PD H-BETA ZEOLITES/

Heptane is isomerized and cracked over Pd/H-Beta zeolite catalysts wit h different palladium loadings (0.1 to 1.0 wt%). On these catalysts, i soheptanes are formed according to two different reaction routes. The classic reaction mechanism is operative and involves monomolecular rea ction steps. A second isomerization pathway exists in which acid catal yzed dimerization of heptene intermediates is followed by cracking int o branched C-7 fragments. The contribution of each of the two mechanis ms on zeolite Beta is deduced from the formation of specific isoheptan es. It depends on the Pd content and the acidity of the zeolite. The m onomolecular mechanism predominates at high Pd loadings, or when the a cidity of zeolite II-Beta is partially poisoned with sodium. The bimol ecular mechanism is active, especially at low metal loadings Of the ca talyst. (C) 1996 Academic Press, Inc.