Abstract: A series of CoMo/γ-Al₂O₃ hydrotreating catalysts with different Co content were prepared and characterized by XRD, H₂-TPR, Raman, XPS and in-situ CO-FTIR analysis. The effect of Co content on the morphology of the active metal and the structure of active phase of the sulfided catalysts were investigated and correlated with the hydrodesulfurization (HDS) activity and polycyclic aromatic hydrocarbons (PAH) saturation activity of the catalysts. The results showed that with the increase of Co content, more CoMoO₄ species were formed on the surface of the catalysts, and the CoMoO₄ species with low crystallinity were more likely to form highly active CoMoS phase during sulfurization, thus improving the HDS activity of the catalyst. However, if the content of Co was too high, more Co₉S₈ phase with low desulfurization activity would be formed and competitive adsorption with CoMoS phase would occur, which would decrease the HDS activity of the catalyst. Because the active sites of catalyst for desulfurization and hydrogenation were not the same, the formation of Co₉S₈ phase did not reduce the aromatics saturation activity of the catalyst. When the mass ratio of CoO to MoO₃ was 0.3, the catalyst had the best HDS activity, and when the mass ratio of CoO to MoO₃ was 0.4, the catalyst has the best PAH saturation activity.

Key words: cobalt oxide, molybdenum oxide, hydrodesulfurization, PHA saturation, active phase