Balance between (De)hydrogenation and Acid Sites: Comparison between Sulfide-Based and Pt-Based Bifunctional Hydrocracking Catalysts

Most industrial hydrocracking catalysts contain metal sulfides. It is commonly accepted that sulfide-based bifunctional hydrocracking catalysts are less well balanced than Pt-based catalysts because of their weak (de)hydrogenation activity. However, the difference in catalytic performances between the two catalysts has never been quantified. In the present work, hydrocracking catalysts were prepared by shaping the USY zeolite CBV720 with an alumina binder. Acidity was varied by changing the USY content. The extrudates were impregnated either with platinum or with nickel-molybdenum-phosphate and evaluated in the hydroconversion of n-hexadecane. In the absence of NH3, NiMo sulfide was unable to supply the acid sites and to avoid cracking reactions. Cracking became the dominating pathway. In the presence of NH3, only a tiny fraction of the acid sites was vacant. This allowed the NiMo sulfide catalysts to become fairly well balanced, if the zeolite loading was low. Increasing zeolite loading led to a deviation from ideality. Pt catalysts were, with one single exception (at very high USY content), always balanced, even in the absence of NH3.