Co-MCM-41 catalysts were synthesized and used to support the additional cobalt. Microcalorimetric adsorption of NH3 showed that the Co-MCM-41 and 5%Co/5%Co-MCM-41 exhibited stronger surface acidity than 5%Co/MCM-41. The surface acidity was greatly enhanced upon the sulfidation. The 5%Co/5%Co-MCM-41 after sulfidation possessed strong surface acidity with an initial heat of about 180 kJ/mol and coverage of about 1060,mu mol/g for the adsorption of ammonia. The catalytic tests showed that little skeletal isomerization occurred on the Co-Mo/gamma-Al2O3, whereas it occurred substantially over the MCM-41 related catalysts. Over 60% skeletal isomerizations were observed for the 5%Co/5%Co-MCM-41 at 573 K. In addition, a combination of the Co/Co-MCM-41 with a traditional Co-Mo/gamma-Al2O3 catalyst showed not only the high hydrodesulfurization activity but also converted significant amounts of 1-hexene into branched hexanes. Thus, this technique might be used to compensate the loss of octane number of gasoline during its hydrodesulfurization by first converting linear olefins to branched ones followed by hydrogenating to branched alkanes.