Characterization and reactivity of sulfided NiNaY zeolite catalysts for thiophene conversion

Abstract

The hydrodesulfurization (HDS) of thiophene has been studied in the presence of hydrogen at 613 K in a fixed-bed flow reactor over a series of sulfided Ni-exchanged Y zeolite catalysts. Both oxidic precursors and sulfided catalysts have been characterized by X-ray photoelectron spectroscopy, infrared spectroscopy of NO and pyridine adsorbed probes, and acidity measurements. Sulfidation led to the formation of sulfided Ni 2+ and, probably, reduced Ni, species that migrated to the external surface layers and to supercages of the zeolite. There is also an important increase of Brönsted acidity. Both HDS (major reaction) and cracking activities increased with increasing Ni content and, therefore, with increasing acidity of the zeolites, and decreased markedly with pyridine poisoning. Precalcination at 873 K or nonsulfidation pretreatments of the Ni-exchanged zeolites led to an important decrease of HDS activity. All the results point out that sulfided Ni-species formed on zeolite are predominantly involved in the HDS of thiophene.