The conversion of n-octane over a series of monofunctional HY zeolites, which differed with the contents of Na and over the bifunctional Pt/HY zeolites differed with the contents of Pt, was studied as function of the balance among the specific activity of the components, the distribution of the metallic sites over zeolite surfaces and reaction conditions. The activities of individual metal and zeolite components were quantified in the reactions of 1-hexene hydrogenation and n-octane cracking, respectively. Gradientless reactors of different configurations were applied to rationalize the contribution of hydrogenation, dehydrogenation, cracking, isomerization, oligomerization, and catalyst deactivation reactions to the reaction pathways over the bifunctional Pt/HY zeolites. The conceptual bifunctional mechanism involving the dehydrogenation of n-octane into olefinic counterparts was demonstrated experimentally by using the flow circulation unit equipped with two reactors connected in series and loaded with separated HY and Pt components. The limiting steps were determined depending on the activity of the Pt component in Pt/HY It was shown that an optimum concentration of Pt sites exists in HY zeolites which corresponds to a maximum cracking activity followed by a significant decrease as the concentration of metallic sites further increases. The effect of diffusion transfer of branched octene intermediates inside the zeolite cavities from the acidic sites to Pt sites on the rates and reaction pathways over Pt/HY zeolites is argued. (C) 2003 Elsevier Inc. All rights reserved.