Synthesis and characterization of Ti-HMS and CoMo/Ti-HMS oxide materials with varying Ti content

Hexagonal mesoporous materials with wormhole framework structures having Si/Ti molar ratios of 80, 40, and 20 (Ti-HMS) were used as supports of CoMo HDS catalysts. The supports and catalysts were characterized by N-2 adsorption-desorption (S-BET), X-ray diffraction (XRD), UV-vis diffuse reflectance spectroscopy (DRS UV-vis), X-ray photoelectron spectroscopy (XpS), Si-29 nuclear magnetic resonance (Si-29 NMR), FT-IR of adsorbed NO, and reactivity. The catalysts were tested in the reaction of hydrodesulfurization (HDS) of dibenzothiophene (DBT). The incorporation of titanium into the framework of HMS did not change its mesoporous character but modified the surface properties. The presence of Ti impedes the formation of CO2SiO4 and of beta-CoMoO4 phases and increases the amount of octahedral Co species. The incorporation of titanium into the HMS framework led to an increase in the catalytic activity in comparison to that of the Ti-free catalyst. All Ti-containing catalysts manifest higher activity than that of a conventional CoMo/Al2O3 catalyst. The effect of Ti is not linear, the highest activity was observed for the sample with Si/Ti = 40 atomic ratio. This catalyst demonstrated to be 30% more active than the conventional industrial catalyst and 50% more active than the Ti-free catalyst. It is suggested that the higher activity of this catalyst is related to the higher value of the Co/Mo ratio in the sulfide state of the catalysts, to the larger amount of exposed Co species and to the specific degree of sulfidation of the Co species, characterized by specific electronic properties, which promote both the DDS and the HYD routes of HDS of DBT. The large pore diameter of this sample should also contribute to the elimination of possible diffusion effects.