Activity and Structure of Hydrotreating Ni, Mo, and Ni–Mo Sulfide Catalysts Supported on γ-Al2O3–USY Zeolite

Abstract

The catalytic hydrocracking (HC) of diphenylmethane (DPM) and hydrodesulfurization (HDS) of dibenzothiophene (DBT) over Ni, Mo, and Ni–Mo sulfide catalysts supported on a mixed ultrastable Y (USY) zeolite and γ-Al2O3 were studied. The catalysts were characterized using NH3 temperature-programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS), UV–Vis–NIR diffuse reflectance spectroscopy (DRS), high-resolution transmission electron microscopy (HRTEM), and chemical composition analysis. Because addition of zeolite to a conventional alumina support improves acidity, Ni, Mo, and Ni–Mo catalysts supported on the combined supports had much higher HC activity. Ni was found to be uniformly distributed throughout the catalysts; however, Mo preferentially entered the structure of γ-Al2O3 or was accommodated as oxide aggregates on γ-Al2O3, rather than associating with zeolite. Ni and Mo catalysts supported on γ-Al2O3–USY zeolite were good HDS catalysts and showed a shallow maximum in catalytic activity at a NiO and MoO3 content of 5 mol%. The higher activity at this content occurred because Ni or Mo species had higher surface concentrations, higher dispersion, and were more easily sulfided. Ni–Mo catalysts supported on γ-Al2O3–USY zeolite had high HDS activity, which showed a prominent maximum at a NiO/(NiO+MoO3) ratio of about 0.4, because at this ratio the surface species of Ni and Mo were well dispersed and more easily sulfided to form a Ni–Mo–S phase responsible for the high HDS activity. The Ni–Mo catalysts supported on γ-Al2O3–USY zeolite have slightly higher HDS activity than γ-Al2O3-supported Ni–Mo catalysts.