To achieve selective hydrodesulfurization (HDS) of fluid catalytic-cracked (FCC) gasoline for producing sulfur-free gasoline (S < 10 ppm), the reactivity of various olefins contained in FCC gasoline on CoMoP/Al2O3 sulfide catalysts was investigated. Isomerization of the C=C double bond from the terminal position to an internal position was observed. The steric hindrance around the C=C double bond suppresses the reactivity of olefin hydrogenation. The sulfidation temperature of the catalyst has a major influence on olefin hydrogenation active sites. Addition of the appropriate amount of cobalt (Co/Mo ratio approximately 0.6) contributes to the suppression of olefin hydrogenation at high reaction temperature (260 degrees C). From the comparison of catalytic performance and characterization of our CoMoP/Al2O3 catalyst with an analogous commercial catalyst, it is suggested that the hydrogenation ofolefins depends not only on the state of the Mo CUS but also on the steric effects of both olefin structure and MoS2 crystalline structure. (c) 2006 Elsevier B.V. All rights reserved.