The dispersion of the active phase and loading capacity of the Mo species on carbon nanotube (CNT) was studied by the XRD technique. The reducibility properties of Co-Mo catalysts in the oxide state over CNTs were investigated by TPR, while the sulfided Co-Mo/CNT catalysts were characterized by means of the XRD and LRS techniques. The activity and selectivity with respect to the hydrodesulfur-ization (HDS) performances on carbon nanotube supported Co-Mo catalysts were evaluated. It was found that the main active molybdenum species in the oxide state MoO_3/CNT catalysts were MoO_2, but not MoO_3, as generally expected. The maximum loading before the formation of the bulk phase was lower than 6% (percent by mass, based on MoO_3). TPR studies revealed that the active species in the oxide state Co-Mo/CNT catalysts were reduced more easily at relatively lower temperatures in comparison to those of the Co-Mo/γ-Al_2O_3 catalysts, indicating that the CNT support promoted or favored the reduction of the active species. The active species of a Co-Mo-0.7/CNT catalyst were more easily reduced than those of the Co-Mo/CNT catalysts with Co/Mo atomic ratios of 0.2, 0.35, and 0.5, respectively, suggesting that the Co/Mo atomic ratio has a great effect on the reducibility of the active species. It was found that the incorporation of cobalt improved the dispersion of the molybdenum species on the support, and a phenomenon of mobilization and re-dispersion had occurred during the sulfurization process, resulting in low valence state Mo_3S_4 and Co-MoS_(2.17) active phases. HDS measurements showed that the Co-Mo/CNT catalysts were more active than the Co-Mo/γ-Al_2O_3 ones for the desulfurization of DBT, and the hy-drogenolysis/hydrogenation selectivity of the Co-Mo/CNT catalysts was also much higher than those of the Co-Mo/γ-Al_2O_3. The Co-Mo/CNT catalyst with a Co/Mo atomic ratio of 0.7 showed the highest activity, whereas the catalyst with a Co/Mo atomic ratio of 0.35 had the highest selectivity.
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