Dealuminated ZSM-12, zeolite beta and their composites with gamma-Al2O3 as a matrix were evaluated for the reforming of an industrial naphtha (rich in naphthenes). The reactions were carried out at temperatures in the 270-470 degrees C range. It was found that dealuminated ZSM-12 demonstrates unique time-on-stream stability for the reactions investigated. This behavior is a combined result of : (a) its pore structure which does not favor coke formation, and (b) the balance of its acidity. Zeolites with channel intersections, which are slightly larger than the zeolite aperture do not favor coke formation. Our results demonstrated that the composite catalysts produce more gasoline-range hydrocarbons and show much better time-on-stream behavior than conventional gamma-Al2O3 catalysts. Fresh and deactivated catalysts were characterized by XRD, NH3-stepwise TPD, TGA, and FTIR. Soluble carbonaceous deposits analyzed by high-resolution GC/MS are mostly paraffinic in nature. The paraffin deposits present over the Pt/gamma-Al2O3 catalyst were of higher molecular weight than those over the zeolite catalysts. We propose that, at relatively lower reaction temperatures, the catalyst deactivates via a successive alkylation type of mechanism in which carbonaceous coking precursors propagate through the continuous addition of olefinic intermediates to carbenium/carbonium ions.