Cobalt -molybdenum-sulfur catalysts preparation

Another SIMS study on model systems concerns molybdenum sulfide catalysts. The removal of sulfur from heavy oil fractions is carried out over molybdenum catalysts promoted with cobalt or nickel, in processes called hydrodesulfurization (HDS) [17]. Catalysts are prepared in the oxidic state but have to be sulfided in a mixture of H2S and H2 in order to be active. SIMS sensitively reveals the conversion of Mo03 into MoSi, in model systems of MoCf supported on a thin layer of Si02 [21]. 

The presulfided catalyst used in this study was industrially prepared of a commercial CoMo type HDS catalyst by the Sulficat Process, impregnation with an organic polysulfide compound followed by fixation at an elevated temperature. The amount of sulfur introduced on the catalyst has been calculated from the theoretical stoechiometry necessary to convert all the molybdenum and cobalt into M0S2 and CoqSg. 

Cobalt-promoted molybdenum sulfides supported on alumina are widely used in petroleum refining for sulfur removal [1]. However, there is now increasing necessity to further improve their performance (activity, selectivity, and stability), due to more and more stringent legislation on sulfur contents in transportation fuels [2]. It is thus primordial to understand the detailed structure and catalytic behavior of these catalysts. In this respect, controlled preparation of catalysts with desired composition and structure has great importance in permitting fundamental study of structure-performance correlation. 

---