Development of hydrodesulfurization catalyst using comparative model feed reactions and quantum chemical studies

Model HDS catalysts (NiW, NiCoMo, NiMo, CoMo/γ-Al₂O₃) were used in the HDS of dibenzothiophene and 4,6-dimethyldibenzothiophene (4,6-DMDBT), with and without the addition of H₂S or NH₃. The highest HDS performance was achieved using NiCoMo catalyst in the presence of additives, while NiMo was the best catalyst in the absence of additives. The hydrogenation (HYD) selectivities of NiMo and NiCoMo catalysts were higher than that of CoMo. The presence of NH₃ significantly decreased the overall reaction rate constant for the conversion of 4,6-DMDBT for the catalysts to a great extent. The addition of NH₃ decreased significantly the reaction rate constant of CoMo catalyst. A comparison of the HDS reaction mechanism via HYD and the direct desulfurization (DDS) rate constants among catalysts showed that the ranking of HYD and DDS rate constants is dependent on the catalyst and the additives. This is an abstract of a paper presented at the 18th Saudi Arabia-Japan Joint Symposium (Dhahran, Saudi Arabia 11/16-17/2008).