Palladium effect over Mo and NiMo/alumina-titania sulfided catalysts on the hydrodesulfurization of 4,6-dimethyldibenzothiophene

The influence of Pd as additive for Ni and Mo catalysts supported on alumina-titania (Mo/AT) sulfided catalysts was investigated in the hydrodesulfurization of 4,6-dimethyldibenzothiophene. Pd incorporation was carried out in the oxidic phases by using sequential impregnation. The alumina-titania support was formed by anatase-TiO(2) crystallites randomly dispersed on gamma-Al(2)O(3). Characterization by X-ray diffraction and Raman spectroscopy revealed that MoOx species for PdMo supported on alumina-titania displayed larger particles than those in PdNiMo catalysts. HRTEM images showed an increase in order and stacking for MoS(2) slabs after Pd addition to NiMo samples, as compared with Mo/AT. Pd incorporation over the NiMo/AT sample increased the reaction rate by 30% while no significant increase was recorded for the PdMo sample. This value corresponds to the most active catalyst and it points out to a promoting effect by Pd. This prominent hydrodesulfurization capacity for the PdNiMo/AT suggests a close interaction of Pd with NiMo. Furthermore, since Pd promoted the HDS activity for a NiMo system, the alumina-titania support played an important role. (C) 2011 Elsevier B.V. All rights reserved.