The effect of presulfidation temperature on the magnetic property, local structure, and intrinsic hydrodesulfurization activity of Co-Mo(W)-S has been studied with SiO2-supported Co-Mo and Co-W sulfide catalysts prepared by exposing presulfided MoS2/SiO2 and WS2/SiO2, respectively, to a vapor of Co(CO)(3)NO. A TPS study shows that complete sulfidation of Mo(W) precursors to Mo(W)S-2 particles is required for the formation of Co-Mo(W)-S Type II. The intrinsic activity of Co-W-S Type II is 1.6 times as high as that of Co-Mo-S Type II. The Co K-edge EXAFS analysis of Co-Mo(W)-S confirms the formation of dinuclear Co sulfide clusters on Mo(W)S-2 edges. The intrinsic activity of Co-Mo-S is correlated with the Co-S-Co anti ferromagnetic interaction strength, suggesting modifications of the electronic state and local structure of Co-Mo-S by MoS2-O-support interactions, in conformity with the EXAFS analysis. (C) 2009 Elsevier Inc. All rights reserved.