Highly Active CoMoS/Al₂O₃ Catalysts ex Situ Presulfided with Ammonium Sulfide for Selective Hydrodesulfurization of Fluid Catalytic Cracking Gasoline

An improved ex situ presulfidation method for the preparation of the CoMoS/γ-Al₂O₃ catalyst was developed with ammonium sulfide as the sulfiding agent, and the prepared catalysts were evaluated in selective hydrodesulfurization (HDS) of fluid catalytic cracking (FCC) gasoline. The selectivity of the ex situ presulfided catalysts was more than 4 times of that of the in situ presulfided catalysts. The characterization by XRD, HRTEM, XPS, TPR, and FT-IR indicated that ammonium sulfide effectively reacted with the supported Mo oxide to form ammonium tetrathiomolybdate as intermediate, thus realizing the more complete sulfidation of Mo oxide. However, the supported Co oxide could not be sulfided by ammonium sulfide, and the delayed sulfidation would not hinder the easy growth of MoS₂ particles, subsequently lead to the significantly longer slab lengths of MoS₂ particles than that of the in situ presulfided catalyst, which effectively decreased the number of active sites for olefins, thus inducing much higher HDS selectivity