(89d) Effect of the Oxide Precursors on the Sulfurability of Hydrotreating Como(P) Catalysts

Introduction- Removal of sulfur impurities in petroleum fractions requires a catalytic process involving CoMo- or NiMo-type catalysts. Their active phases are consisting of molybdenum disulfide slabs promoted by cobalt or nickel atoms that are well dispersed on a high specific area alumina. As the highest sulfur content allowed in gasoline and diesel is continually decreasing, more and more efficient hydrotreatment catalysts are required. Improvement of these catalysts imposes to have a better understanding of the structure and genesis of the CoMoS active phase. Thus, a procedure to characterize this mixed phase has been established. In this context, a multi-techniques approach correlating X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) with activity measurements has been conducted. This methodology of characterization was used to study the effect of the nature of the oxide phase precursors on the sulfurability of CoMo(P) catalysts and consequently on the formation of the CoMoS phase. Experimental section- Oxidic CoMo- and CoMoP-type precursors were prepared by impregnation of an alumina support with solutions containing the elements to be deposited. The use of cobalt salts of Co₂Mo₁₀O₃₈H₄^6- [1] and P₂Mo₅O₂₃^6- [2] has enabled the preparation of CoMo and CoMoP catalysts with high molybdenum loading and an oxide phase evenly spread out in the alumina framework. The oxidic precursors were activated by sulfidation with a H2S/H2 (15%-85%) gas mixture. Results and conclusion- The objective of this work was to study the effect of the nature of the oxide phase precursor on the formation of the active phase during the sulfidation step. We have characterized various CoMo and CoMoP catalysts prepared by using heteropolycompounds and sulfided at different temperatures. XPS characterization, TEM analysis and toluene-hydrogenation activity measurements allowed us to highlight that the nature of the heteropolycompound used to prepare the oxidic precursor has an influence on the sulfurability of the catalysts. So we have determined the better way of preparation and the optimal sulfidation temperature for the hydrotreatment catalysts that we have studied. [1] C. Martin, PhD thesis, Lille (2003) - [2] A. Griboval et al., Catal. Today, 45, 277-283 (1998)