D. Li et al., Zeolite-supported Ni and Mo catalysts for hydrotreatments - I. Catalytic activity and spectroscopy, J CATALYSIS, 182(2), 1999, pp. 339-348
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.