Morphological and Structural Properties of MoS_2 and MoS_2-Amorphous Silica-Alumina Dispersed Catalysts for Slurry-Phase Hydroconversion

摘要

Unsupported MoS2 and bifunctional MoS2-amorphous silica-alumina (ASA) catalysts, active for hydrogenation and hydrocracking reactions, were obtained by in situ thermal decomposition of molybdenum octoate in the presence of a sulfur source at temperatures between 300 and 400 degrees C. Unsupported MoS2 was formed at temperatures as low as 300 degrees C with yields higher than 76%. Increasing temperature increased the degree of sulfidation but also increased particle dimensions and, consequently, decreased the MoS2 dispersion. The presence of ASA reduced MoS2 particle dimensions compared to the unsupported MoS2, while the effect on sulfidation degree was dependent on temperature. High temperature (400 degrees C) was required to achieve high MoS2 yield due to interactions with the support at lower temperatures. The catalytic activity of the unsupported MoS2 showed that, as a result of the opposing effects of temperature on the MoS2 dispersion and MoS2 sulfidation degree, the activity toward hydrogenation of phenanthrene, reported on a per edge site basis, was not affected by morphological and structural differences. The bifunctional MoS2-ASA catalyst at 400 degrees C promoted cracking, isomerization, and ring-opening reactions due to the moderate Bronsted acidity of the ASA and changed the product distribution favorably when compared to the unsupported MoS2.