EFFECT OF COBALT ON THE SULFIDING TEMPERATURE OF COO-MOO3 AL2O3 STUDIED BY TEMPERATURE-PROGRAMMED SULFIDING/

The effect of cobalt on the sulfiding temperature of CoO-MoO3/Al2O3 wa s investigated by means of temperature programmed sulfiding (TPS). MoO 3 supported on alumina transforms into MoS2-x by sulfidation via forma tion and subsequent hydrogenation of Mo oxi-sulfide or MoS3. The tempe rature of which the Mo oxi-sulfide or MoS3 phase are hydrogenated (Ps temperature) decreased with increasing amount of cobalt in the CoO-MoO 3/Al2O3 catalysts. A decrease in the Ps temperature was also observed in the case of 'Co/Al+Mo/Al catalysts' which were prepared by mechanic al mixing of CoO/Al2O3 and MoO3/Al2O3. On the other hand, the Ps tempe rature did not change by mechanical mixing of bulk CoO and the MoO3/Al 2O3 catalyst. The cobalt adsorption test suggested that the cobalt spe cies preferably interact with the molybdenum species during impregnati on. It was concluded that the well dispersed cobalt species have a cap ability to provide spillover hydrogen to accelerate the hydrogenation of the Mo oxi-sulfide. Furthermore, a correlation between the Ps tempe rature and HDS activity for light gas oil was obtained. This result su ggests that the cobalt species facilitate the hydrogenation of sulfur atoms adsorbed on the HDS active sites (coordinatively unsaturated Mo sites) by supplying spillover hydrogen and consequently accelerate the HDS reaction. (C) 1997 Elsevier Science B.V.