Hydrodesulfurization of refractory sulfur species. 2. Selective hydrodesulfurization of 4,6-dimethyldibenzothiophene in the dominant presence of naphthalene over ternary sulfides catalyst

The catalytic activities of sulfided Ru-CoMo/Al₂O₃ were examined for the desulfurization of 4,6-dimethyldibenzothiophene (4,6-DMDBT) in decane and decane with naphthalene to find selective catalysts which desulfurize 4,6-DMDBT in the presence of naphthalene through preferential hydrogenation of its phenyl ring. Addition of Ru to CoMo catalyst exhibited an excellent activity for HDS of 4,6-DMDBT and suffered less inhibition by coexisting naphthalene, whereas significant retardation was observed over NiMo/Al₂O₃ and Ru-NiMo/A₂O₃. The ternary combination required much less amount of Ru to maximize the selective HDS reaction, compared to the blend of Ru/Al₂O₃ and CoMo/Al₂O₃. Several structural characteristics of the ternary catalyst were revealed according to XPS and HREM: (1) Mo and Ru existed separately on the same alumina support in forms of respective sulfides, (2) crystal size of MoS₂ increased when Ru was present on the same support, and (3) MoS₂ was easily reduced in the presence of Ru. RuS₂ is suggested as the site for the selective hydrogenation of 4,6-DMDBT, the hydrogenated product of which is transferred immediately to the Co-Mo-S active site to be desulfurized.