TiO2-supported Mo (6 and 12 wt.%) and Fe (0.25-1.0 wt.%) containing catalysts have been prepared using H3PMo12O40 heteropolyacid (HPMo) and Fe salt of HPMo. Catalysts have been characterized by BET, SEM, IR, TPR, XPS methods and by their HDS activity in the reaction of thiophene conversion. Promoting effect of TiO2 on Mo catalysts was confirmed, higher in case of catalysts with low Mo concentration (6) wt.%) than in case of the catalyst with 12 wt.% Mo. The highest HDS activity and stability was observed after introducing Fe in the form of HPMo countercation (Fe/Mo similar to 0. 1). Iron increases concentration of Mo6+ and Mo5+ in octahedral coordination. After sulfidation, the Fe-containing catalysts show presence of different Mo valence states (Mo4+, Mo5+, Mo6+), Fe-P, Mo-P and/or Fe-Mo-P bonds that affect the HDS catalytic activity. (c) 2005 Elsevier B.V. All rights reserved.