CHARACTERIZATION OF TUNGSTEN-MODIFIED ULTRASTABLE Y-ZEOLITE CATALYSTS AND THEIR ACTIVITY IN THIOPHENE HYDRODESULFURIZATION

Tungsten-modified ultrastable Y (USY) zeolite catalysts, prepared by conventional impregnation with ammonium metatungstate solutions at three different pHs and calcined at 350, 450, and 550°C have been characterized by X-ray diffraction (XRD), infrared spectroscopy (IR), scanning electron microscopy-energy dispersive X-ray analysis (SEM-EDX). and acidity and surface area measurements. They have also been evaluated for hydrodesulfurization (HDS) of thiophene and subsequent hydrogenation (HYD) of butenes in both oxidic and sultided states. The incorporation of tungstate ions in the USY followed by calcination at high temperature was found to cause a small loss of crystallinity, particularly for the catalysts impregnated at acidic pH. In this case, the EDX and N2 adsorption results indicated that most of tungsten was inhomogeneously deposited outside the zeolite cavities, but without forming WO3 species that could be detected by XRD. This location of tungsten and the increased acidity after sulfidation with H2S generated a substantial increase in HDS activity relative to the parent USY, and the appearance of HYD activity. Conversely, in the catalysts prepared at basic pH, a large part of the tungsten is inside the zeolite cavities, most probably in the supercages. This tungsten location and the loss of acidity resulted in a very low HDS activity and no HYD activity for both calcined and sulfided catalysts. © 1993 Academic Press, Inc.