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, an d their thiophene hydrodesulfurization (HDS) activity and acidity were evaluated. A nickel-exchanged zeolite sample treated with a NaOH solu tion was also investigated. As regards to oxidic samples, significant differences in reducibility and, consequently, location of the Ni2+ io ns, which were mainly inside the zeolite cavities, were found. After s ulfidation such differences were minor since most of the nickel sulfid e species migrated to the mesopores of the zeolite particles. The zeol ite samples having only one type of active site, either acidic (prepar ed at pH 2.7) or nickel sulfide species (treated with a NaOH solution) , showed a low thiophene HDS activity. However, those that have both t ypes of sites, such as the samples prepared at pH 5.6 and it (NH4OH me dium), exhibited a high activity for thiophene HDS and also for subseq uent hydrogenation of butenes.