Effect of coordinating groups of chelating agents on the hydrodesulfurization over CoMo/γ-Al₂O₃ catalysts

The modified CoMo/γ-Al₂O₃ catalyst was prepared by addition of ethylene diamine (EN), ethanolamine (EA), ethylene glycol (EG) or malonic acid (MA). The effect of four bidentate molecules with different coordination groups on the dibenzothiophene HDS was compared. And the catalytic activity is determined in the sequence of CoMo (EN) > CoMo (EA) > CoMo (EG)≈CoMo (MA) > CoMo. For all catalysts, the direct desulfurization route is dominated, but with the increase of reaction temperature, the desulfurization by hydrogenation route become more apparent. Chelating agents facilitate the HDS reaction through hydrogenation route. CoMo (EN) catalyst presents the highest hydrogenation ability. The catalysts were characterized by UV-vis, EA, XPS and HRTEM. The results show that NH₂ group has a strong complexing interaction with Co²⁺. COOH group mainly has an electrostatic interaction with cobalt ion. Meanwhile, OH group hardly interacts with Co²⁺. It is noted that the HDS activity is directly related to the interaction between coordinating groups and Co²⁺. The combination of coordinating molecules with Co²⁺ leads to the effective formation of Co-Mo-S active center, and the carbonization of chelating decreases the interaction of the support with active phases, facilitating the formation of type Ⅱ active phases which has a higher intrinsic catalytic activity.