Optimization of the synthesis technique of molybdenum sulfide catalysts supported on titania for the hydrodesulfurization of thiophene

The present work deals with the optimization of the preparation method for the synthesis of unpromoted molybdenum catalysts supported on titania. Four methodologies have been followed: equilibrium–deposition–filtration (EDF), wet impregnation (WI), dry impregnation (DI) and controlled wet impregnation (CWI). The Mo surface density of all catalysts was 3.2 Mo atoms/nm2. The catalysts were characterized using N2 adsorption, XRD, XPS and DRS. The catalysts were evaluated in the hydrodesulfurization (HDS) of thiophene, using an atmospheric differential fixed bed reactor. EDF technique provided the most active catalyst followed by that prepared by WI and then by those prepared by DI or CWI. Although the impregnation technique does not influence the structure of the catalysts at nanoscale, a suitable choice of the impregnation technique leads to the increasing contribution of supported molybdenum clusters with small size and thus with high number of the Ti–O–Mo (Ti–S–Mo) bridges per Mo atom, stabilizing highly S-deficient structures. In order to confirm the favorable influence of titania on the catalytic performance, we have synthesized by DI a Mo catalyst supported on γ-alumina with the same loading. The relatively low activity exhibited by this catalyst was attributed to the different structure of the supported molybdenum species with respect to those formed on titania and to the lower Mo dispersion.