Catalysis Today, Vol.305, 65-74, 2018
Enhancement of dibenzothiophene hydrodesulphurization via hydrogenation route on NiMoW catalyst supported on HMS modified with Ti
This study shows that ternary Ni-Mo-W sulfide catalysts supported on hexagonal mesoporous silica modified with Ti (HMS-Ti) showed a high enhancement of dibenzothiophene (DBT) transformation via hydrogenation route with respect to their Ti-free counterpart. The reaction of hydrodesulphurization (HDS) of DBT was carried out at in a batch reactor at 320 degrees C and 5.5 MPa of total H-2 pressure. The catalysts were characterized by a variety of techniques (chemical analysis, N-2 adsorption-desorption isotherms, low-and wide-angles XRD, TPR, TPDNH3, DRS UV-vis, TPO/TG and HRTEM). At reaction time of 5 h, all synthetized catalysts exhibited higher DBT conversion (84-100%) than both commercial NiMo/gamma-Al2O3 and NiW/gamma-Al2O3 catalysts (59 and 69%, respectively). For all catalysts, the DBT transformation occurs via direct desulfurization (DDS) and hydrogenation (HYD) pathways. The DDS was the main reaction route for Ti-free sample whereas for both Ti-containing samples the DBT transformation occurs mainly via HYD reaction route. At a reaction time of 5 h, the best catalyst (NiMoW/HMS-Ti1) exhibited 100% of DBT conversions and the highest yield of hydrogenation route products. From the activity results, it is concluded that only the structure of Ti species is relevant for the catalyst activity, but not the amount of Ti incorporated in the HMS framework. The superior activity of sulfide NiMoW/HMS-Ti1 is linked with the best properties of its oxide precursor: a lowest band energy gap and a large amount of Mo (W)(6+) ions having octahedral coordination. After sulfidation, the best catalyst exhibited the "onion-type" Mo(W) S-2 structures which offer the best conditions for the formation of "bright rim" Mo edge sites, which are known to be active sites for DBT transformation via HYD reaction route.