Nature of cobalt active species in hydrodesulfurization catalysts: Combined support and preparation method effects

Co/?-Al2O3, Co/SiO2, Co/MCM-41, Co/ASA and Co/S2 (amorphous aluminosilicate with Al/Si = 0.13 and with Al/Si ? 2, respectively) were prepared by the method of wet impregnation and by the method of precipitation in the presence of sodium carbonate. The samples were characterised by XPS, XRD and TPR. The catalytic activity was tested in the hydrodesulfurization of thiophene using a continuous flow reactor. Among the wet impregnated catalysts those supported on the amorphous and ordered mesoporous silica exhibited higher HDS activity as compared to the alumina containing supports. Particularly, the use of the mesoporous, high surface area MCM-41 support, determined the best performing cobalt catalyst. Quite surprisingly, the catalytic performance of the cobalt catalysts was completely reversed by using the method of precipitation with sodium carbonate. In this case the alumina supported catalyst was the most active. For the wet impregnated samples, the positive influence of SiO2, as compared to the aluminosilicates, was related to the formation of Co3O4 which on the other supports was hindered by the interaction with alumina. On the contrary, using the method of precipitation with sodium carbonate, Co3O4 formed on the alumina containing supports, whereas cobalt-support interacting species formed over the two types of SiO2. Increased cobalt reducibility and cobalt dispersion accounted for the different catalytic behaviour. © 2007 Elsevier B.V. All rights reserved.