Molybdocobaltate cobalt salts : new starting materials for hydrotreating catalysts
Résumé
This paper deals with the use of Anderson heteropolyanions as alternative starting materials to the ammonium heptamolybdate and cobalt nitrate for the preparation of hydrotreatment oxidic precursors. Ammonium and cobalt salts of molybdocobaltate anions were synthesized and impregnated on alumina. The evolution of these compounds along the different steps of preparation of the oxidic precursors has been followed using various physical techniques such as Raman, XAS and UV–vis spectroscopies. It has been shown that the nature of the surface oxomolybdenum phase strongly depends on the nature of the starting salt. After sulfidation under H2/H2S, the performances of these new catalysts have been evaluated in hydrodesulfuration of thiophene. It appears that the cobalt salt of the decamolybdocobaltate anion [Co2Mo10O38H4]6, with a Co/Mo ratio equal to 0.5, allows us to improve the catalytic conversion by comparison to reference catalysts prepared with ammonium heptamolybdate and cobalt nitrate as starting materials. It has been shown that this improvement is due to the preservation of the heteropolyanionic structure up to the drying step.