FLUORINATED HYDROTREATMENT CATALYSTS EFFECT OF THE DEPOSITION ORDER OF F(-) IONS ON F-COMO/GAMMA-AL2O3 CATALYSTS

In order to elucidate the influence on the hydrodesulphurization (HDS) activity of the order of deposition of F- ions on CoMo/gamma-Al2O3-F catalysts, we prepared, characterized (using BET, NO chemisorption, DRS and XPS) and determined the HDS activity (at atmospheric pressure and various temperatures using the HDS of thiophene as model reaction) of four samples. Specifically, we prepared one undoped CoMo/gamma-Al2O3 catalyst (denoted as MC) and three fluorinated catalysts in which the F- ions were deposited before (FMC), after (MCF) and simultaneously with the Mo(VI) and Co(II) phases ( (MCF) ). All the specimen which were prepared contained a fixed amount of Mo (11.5 wt.-% MoO3), Co (3.5 wt.-% Co3O4) and F (0.8 wt.-% F). It was found that a change in the deposition order provoked a change in the specific surface area, in the dispersity of the supported Mo and Co species and in the intrinsic activity of each HDS active site. The last change was found to be related to the ratio Mo(octahedral)/Mo(tetrahedral). Moreover, it was inferred that fluorination increased the number of active sites per unit active surface. The above explained the changes in the density of the HDS active sites, in the number of these sites and finally on the HDS activity which follows the order MCF> FMC > MC > (MCF) in all temperatures studied. Finally, an attempt was made to convincingly develop pictures related to the preparation which explain the influence of the F doping on the specific surface area and dispersity of the Mo and Co supported species.