Highly active CoMoS phase on titania nanotubes as new hydrodesulfurization catalysts

A series of CoMoS on nanotubular TiO2 (NT) catalysts were prepared by incipient impregnation at Mo = 3–5 atoms/nm2 and Co/(Co + Mo) = 0.2–0.4. A nanotubular TiO2 (NT) of 5.5 nm inner diameter, 236 m2/g surface area and 0.5 cm3/g total pore volume was prepared and used as support. The CoMoS/NT catalysts were characterized mainly by Raman and XPS spectroscopies, HRTEM and HAADF (high angle annular dark field) detector. The sulfided catalysts were tested in the hydrodesulphurization (HDS) of dibenzothiophene at 320 °C and 56 kg/cm2. Inorganic fullerene-like MoS2 and/or CoMoS particles, made up of 2–6 structural layers, depending on the Co/(Co + Mo) ratio, were observed, smeared along the nanotubes. An estimation of CoMoS phase surface density (δ), after taken into account all sulfided species quantified by XPS spectra, indicated that highest HDS activity (43 × 10−4 m3/kgMo s) is attained when Mo = 5 atoms/nm2 and Co/(Co + Mo) = 0.3. In comparison, at a lower (0.2) or higher (0.4) Co/(Co + Mo) ratio, either segregated MoO3 or Co9S8 phases were detected, respectively, with Co sulfidability decreasing 60–42%, respectively, and HDS activity being considerably lower.