NaY zeolites containing different types of nickel species were prepared. The effects of temperature, time and H~2S concentration on sulfidation of the zeolites were investigated. The NiO impregnated zeolite samples are sulfided most readily, while the isomorphous substituted Ni heteroatom bearing zeolite is the hardest to be sulfided. The thermal and hydrothermal stabilities of the sulfide species formed on the zeolite surface were studied. Water desorbed from the zeolite at elevated temperature may cause the hydrolysis of the sulfides and thus leads to the desulfidation of the catalysts. The sulfided Ni-containing zeolite catalysts were characterized by means of XRD, IR and chemical analysis. The nickel sulfide formed on the zeolites after sulfidation is probably Ni~7S~6 with an orthorhombic symmetry. Sulfided Ni heteroatom bearing Y zeolite is not active towards thiophene conversion reaction. The hydrodesulfurization activity of the sulfided Ni^2^+ exchanged zeolites is 5-6 times higher than that of the sulfided NiO impregnated zeolites due to their higher acidity. The coexistence of acid sites and nickel sulfide sites on the zeolite will promote the thiophene hydrodesulfurization reaction significantly.

Key words: CATALYST, NICKEL, HYDRODESULFURIZATION, THERMAL STABILITY, CURING, HYDROTHERMAL STABILITY, NICKELOUS SULFIDE