Essential role of promoter Co on the MoS₂ catalyst in selective hydrodesulfurization of FCC gasoline

The essential role of Co on the MoS₂ catalyst in selective hydrodesulfurization (HDS) of FCC gasoline was investigated with ammonium tetrathiomolybdate supported on alumina modified with various amount of Co sulfide. According to the data obtained by XRD, HRTEM, XPS, H₂-TPR and Py-FTIR analysis, the Co species could significantly affect the microstructure and composition proportion of the active phase, and thus induced the enormous differences in catalytic properties. The evaluation results demonstrated that the Co atoms tending to form the CoMoS phase as Co/Mo(atomic ratio) < 0.2 could greatly improve the HDS activity, but slightly improve the hydrogenation (HYD) activity of olefins. The spillover hydrogen produced by the formation of Co₉S₈ phase as 0.2 < Co/Mo(atomic ratio) < 0.6 greatly improved the HDS activity, but showed almost no effect on the HYD of olefins. The excess Co could inevitably form some large size Co₉S₈ phase as Co/Mo(atomic ratio) > 0.6, which would hinder the mutual contact of the reactants and the active sites, and thus lead to the decrease of the HDS activity and selectivity. The obtained results were useful for developing highly effective hydrotreating catalyst.