Activity of Amorphous NiB/SiO₂ in Hydrotreating Model Reactions: Hydrodesulfurization of 4,6-DMDBT

For the first time, we examined the catalytic performance of a NiB/SiO₂ catalyst with 10 wt % NiB in model hydrodesulfurization of 4,6-dimethyldibenzothiophene (4,6-DMDBT) also together with a competing nitrogen compound, that is, carbazole. The NiB/SiO₂ catalyst (fresh, reduced, and spent) was characterized using the following techniques: N₂ sorption, ICP, XRD, CO chemisorption, XPS, and elemental analysis. The results of XRD, XPS, and elemental analysis indicated the partial decomposition of the NiB phase into metallic nickel (accompanied by boron atoms) and partial sulfidation into Ni₃S₂ species under reaction conditions. FT-IR spectra have shown the formation of -SH moieties on the NiB/SiO₂ surface. As revealed in the distribution of the products, regardless of the reaction mode (in the absence or presence of carbazole), the dominant conversion pathway for 4,6-DMDBT was its hydrogenation (HYD route) to 3-(3'-methylcyclohexyl)-toluene (MCHT). The efficiency of dimethylbiphenyl (3,3'-DMBPh) formation was low and was weakly dependent on contact time. Furthermore, it was found that the donation of electrons from B to Ni species tuned the electron structure, not only enhancing the selectivity of the HYD pathway but also improving the thioresistance of the catalyst. As a result of the strong adsorption of carbazole on the catalytic centers, the phenomenon of hindering the transformation of 4,6-DMDBT is observed. Nevertheless, the NiB/SiO₂ catalyst was found to be active in the HDS reaction for about 100 h.