Zeolite-supported Ni and Mo catalysts for hydrotreatments - I. Catalytic activity and spectroscopy

The catalytic hydrodesulfurization (HDS) of dibenzothiophene (DBT) and hydr ocracking (HC) of decalin, tetralin, and diphenylmethan (DMP) over Ni-Mo su lfide catalysts supported on ultrastable Y-type (USY) zeolite have been stu died. The catalysts are characterized using NH3 temperature-programmed deso rption (TPD), X-ray photoelectron spectroscopy (XPS), UV-vis-NIR diffuse re flectance spectroscopy (DRS), and Na and Al K-edge X-ray absorption near-ed ge structure (XANES). Ni-Mo sulfide catalyst supported on USY zeolite has a n unusually high catalytic activity for the hydrotreating reactions of the model compounds compared with other zeolites and their supported catalysts, NH3 TPD shows the presence of a strong acid site at about 430 degrees C in USY zeolite and its supported Ni-Mo catalyst, which is dominantly characte rized by Bronsted acidity. The surface concentrations of Ni and Mo in both calcined and sulfided Ni-Mo/USY zeolite catalysts are very low, indicating that the Ni and Mo phases are present in the crystal structure of USY zeoli te. The diffuse reflectance spectra of calcined Ni-Mo/USY catalyst show tha t Mo is dominantly four-coordinate with oxygen and Ni is six-coordinate, co nsistent with the Ni and Mo species being present in the crystal structure of USY zeolite, Al Kedge XANES spectra of calcined Ni-Mo/USY catalyst also indicate the presence of extra-framework Al, and the content of the extrafr amework Al is much higher in Ni-Mo/USY than in Ni-Mo/NaY catalyst. However, there is no evidence that the extra-framework Al contributes to the acidit y and the increased catalytic activity. Thus, the high catalytic HDS and HC activities of Ni-Mo/USY compared with other zeolites and their supported N i-Mo catalysts are attributed to the synergistic effect between the strong Bronsted acid sites and the Ni and Mo sulfide phases in the sodalite cage a nd/or supercage of USY zeolite. (C) 1999 Academic Press.