Vanadia containing alumina (Vx-Al2O3) was prepared by the co-precipitation method and used as a catalyst support for Co and Mo oxide (Co-Mo/Vx-Al2O3) in the hydrodesulfurization (HDS) reaction. Incorporation of vanadia in the support shifted the reaction mechanism from the direct desulfurization (DDS) pathway to the hydrogenation (HYD) pathway, and hence promoted the activity of Co and Mo oxide for the HDS reaction of the most sterically hindered compound, 4,6-dimethyldibenzothiophene. Detailed catalyst characterization and catalyst testing showed that the promoter effect of vanadia is due to the synergetic effect of the formation of V-Mo sulfide. A binary powder mixture with intimate contact of Co-Mo/gamma-Al2O3 and Co-Mo/Vx-Al2O3 could facilitate a concerted reaction involving both HYD and DDS pathways. Such a binary powder mixture was shown to yield a high conversion and excellent sulfur removal efficiency for the most refractory sulfur compounds in the production of clean diesel fuels. (C) 2010 Elsevier Inc. All rights reserved.