Bimetallic Ni-Mo/gamma-Al2O3 catalysts (Ni20MoX, Ni = 20 wt.%, X= 0, 3, 5, 7, and 9 wt.%) with different Mo contents were prepared using a co-impregnation method. The role and effect of Mo on the catalytic performance of the Ni-Mo/gamma-Al2O3 catalysts in the auto-thermal reforming of ethanol was examined. It was found that the addition of Mo up to 7 wt.% decreased the interaction between the Ni species and the alumina support, increasing the reducibility of Ni species. On the other hand, the Ni20Mo9 catalyst was less effective in hydrogen production than the Ni20Mo7 catalyst due to the formation of bulky NiMoO4 in the Ni20Mo9 catalyst. It was also revealed that Mo species served as a barrier for preventing the growth of Ni particles, leading to the formation of highly dispersed Ni-Mo/gamma-Al2O3 catalysts. In the auto-thermal reforming of ethanol, bimetallic Ni20MoX catalysts (X= 3,5, and 7 wt.%) catalysts exhibited a higher catalytic performance than the monometallic Ni20 catalyst. Among the catalysts tested, the Ni20Mo5 catalyst showed the best catalytic performance. However, addition of excess Mo (9 wt.%) decreased the catalytic performance of the bimetallic supported catalyst, resulting from both poor reducibility of Ni species and coverage of Ni sites by MoOx species. It was also observed that the Ni20 catalyst experienced a severe catalyst deactivation due to coke deposition on the catalyst surface during the catalytic reaction. (c) 2006 Elsevier B.V. All rights reserved.