Chromium Species as Captors of Sulfur Molecules on Nickel-Based Hydrotreating Catalysts

Three nickel-chromium catalysts supported on aluminated mesoporous silica (SBA-15) were prepared with a fixed nickel loading of 15 wt % and differing chromium contents, which ranged between 2.6 and 5.2 wt %. They were tested in the hydrotreating of tetralin in the presence of dibenzothiophene (DBT). Moreover, a monometallic nickel catalyst was also prepared and tested, for comparison. Information regarding the structure of the calcined, reduced, and used catalysts was obtained by several physical-chemical techniques such as X-ray diffraction (XRD), hydrogen temperature-programmed reduction (H-2-TPR), temperature-programmed desorption of ammonia (NH3-TPD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and elemental chemical analysis. The presence of small amounts of Cr3+ ions not only modifies the nickel dispersion, leading to the formation of a more active catalyst in the hydrogenation of tetralin, but also has a strong influence on the stability of these catalysts in the presence of 425 ppm DBT in the feed. The Cr3+ ions seem to act as a sulfur trap, thus preventing sulfur poisoning of nickel particles.