Hydrodesulfurization of dibenzothiophene on Ni-Co alloy boride catalysts supported on alumina

Mixed Ni-Co boride alloys supported on alumina and varying the Ni/(Co+Ni) ratio as: 0.00, 0.25, 0.50, 0.75, and 1.00 were synthesized by the chemical reduction method using a potassium borohydride solution. The black precipitates obtained were characterized by different physic-chemistry techniques such as X-ray diffraction (XRD), Fourier-transformed infrared spectroscopy (FT-IR), surface measurements (BET specific area, pore volume and pore diameter), chemical analysis, elemental analysis, temperature programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The results of characterization showed the formation of amorphous Ni-Co boride alloys. These solids were tested in the reaction of hydrodesulfurization (HDS) of dibenzothiophene (DBT). The results showed a behavior of a volcano-like curve as a function of the Ni content in the alloy with a maximum at Ni/(Co+Ni) ratio of 0.5. These results agree with the degree of reduction confirmed by TPR. On the other hand, these catalysts showed more hydrogenating that hydrodesulfurizing properties, which could be related to the active phases present in these boride alloys. Two actives phase are proposed as responsible for this activity: metallic Co and Ni (responsible for the hydrogenation properties) and Co and Ni borides (responsible for the hydrodesulfurization properties). Furthermore, kinetic studies for HDS of DBT were carried out using these catalysts and the results showed that these catalysts follow the classical mechanism of HDS of DBT, where two catalytic sites are proposed.