THIOPHENE HYDRODESULFURIZATION ON SULFIDED NICKEL-EXCHANGED USY ZEOLITES - EFFECT OF THE PH OF THE CATALYST PREPARATION

Nickel-containing ultrastable HY zeolites prepared by ion exchange at pH 2.7, 5.6 and 11 (NH4OH medium) were characterized in oxidic and/or sulfided state by X-ray diffraction, temperature-programmed reduction, scanning electron microscopy and energy dispersive X-ray analysis, and their thiophene hydrodesulfurization (HDS) activity and acidity were evaluated. A nickel-exchanged zeolite sample treated with a NaOH solution was also investigated. As regards to oxidic samples, significant differences in reducibility and, consequently, location of the Ni2+ ions, which were mainly inside the zeolite cavities, were found. After sulfidation such differences were minor since most of the nickel sulfide species migrated to the mesopores of the zeolite particles. The zeolite samples having only one type of active site, either acidic (prepared at pH 2.7) or nickel sulfide species (treated with a NaOH solution), showed a low thiophene HDS activity. However, those that have both types of sites, such as the samples prepared at pH 5.6 and it (NH4OH medium), exhibited a high activity for thiophene HDS and also for subsequent hydrogenation of butenes.