DEALUMINATED ZEOLITE-BASED COMPOSITE CATALYSTS FOR REFORMING OF AN INDUSTRIAL NAPHTHENE-RICH FEEDSTOCK

Dealuminated ZSM-12, zeolite beta and their composites with gamma-Al2O 3 as a matrix were evaluated for the reforming of an industrial naphth a (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 invest igated. This behavior is a combined result of: (a) its pore structure which does not favor coke formation, and (b) the balance of its acidit y. Zeolites with channel intersections, which are slightly larger than the zeolite aperture do not favor coke formation. Our results demonst rated that the composite catalysts produce more gasoline-range hydroca rbons and show much better time-on-stream behavior than conventional g amma-Al2O3 catalysts. Fresh and deactivated catalysts were characteriz ed by XRD, NH3-stepwise TPD, TGA, and FTIR. Soluble carbonaceous depos its analyzed by high-resolution GC/MS are mostly paraffinic in nature. The paraffin deposits present over the Pt/gamma-Al2O3 catalyst were o f higher molecular weight than those over the zeolite catalysts. We pr opose that, at relatively lower reaction temperatures, the catalyst de activates via a successive alkylation type of mechanism in which carbo naceous coking precursors propagate through the continuous addition of olefinic intermediates to carbenium/carbonium ions. (C) 1998 Elsevier Science B.V.