Mechanisms of Heptane Isomerization on Bifunctional Pd/H-Beta Zeolites

Abstract

Heptane is isomerized and cracked over Pd/H-Beta zeolite catalysts with different palladium loadings (0.1 to 1.0 wt%). On these catalysts, isoheptanes are formed according to two different reaction routes. The classic reaction mechanism is operative and involves monomolecular reaction steps. A second isomerization pathway exists in which acid catalyzed dimerization of heptene intermediates is followed by cracking into branched C₇fragments. The contribution of each of the two mechanisms on zeolite Beta is deduced from the formation of specific isoheptanes. It depends on the Pd content and the acidity of the zeolite. The monomolecular mechanism predominates at high Pd loadings, or when the acidity of zeolite H-Beta is partially poisoned with sodium. The bimolecular mechanism is active, especially at low metal loadings of the catalyst.