ABSTRACT
Catalyti-cally, molecular shape selectivity by size exclusion can be achieved either through reactant selectivity or product selectivity. Alternative interpretations of the experimental results, on the basis of size exclusion and configurational diffusion inhibition, were ruled out by intramolecular isomerization experiments, which indicated that diffusion of symmetrical trialkylbenzenes in mordenite is not hindered. Kim et al. studied the alkylation of ethylbenzene with ethanol over ZSM-5 and concluded that the transition state selectivity plays the major role in forming the primary product, p-diethylbenzene. However, subsequent studies on the aromatization of n-hexane over Pt clusters supported on a high surface area MgO catalyst led to some doubt on the significance of the confinement effect on the selectivity of this reaction. Several zeolites, such as ZSM-4 and mordenite, show remarkable activity and selectivity for the isomerization and disproportionation of light paraffins.
