Al₂O₃ Concentration Effect on Deep Hydrodesulfurization of 4,6-Dimethyldibenzothiophene over NiWS/Al₂O₃–ZrO₂ Catalysts

The Al₂O₃ concentration effect over NiWS/Al _<i>x</i> Zr_100-<i>x</i> catalysts was investigated for deep hydrodesulfurization (HDS) of 4,6-dimethyldibenzothiophene (4,6-DMDBT). The sol-gel method changed the wt % Al₂O₃ concentrations used to synthesize the Al _<i>x</i> Zr_100-<i>x</i> supports. The NiWS/Al _<i>x</i> Zr_100-<i>x</i> catalysts were prepared with ammonium metatungstate hydrate and nickel(II) nitrate hexahydrate by sequential incipient impregnation, calcination, and H₂S/H₂ activation. The catalytic evaluation data fit a pseudo-first-order trend in the 4,6-DMDBT HDS reactions. In the oxide phase, the catalysts presented Ni and W species in tetrahedral (td) and octahedral (oh) coordination, with the oh species prevailing as a function of the Al₂O₃ amount. The lower amount of Al₂O₃ can facilitate the "Type II" NiWS phase formation by weakening the interaction of the W-O-Al bond and promoting W and Ni species sulfidation. In the sulfide phase, catalysts with (oh) coordination and surface WO <i>_X</i> species promote the formation of WS₂ and NiWS species during the catalyst activation step. This species favors the reaction yield, where the hydrogenation route is predominant, with the highest initial reaction rate using the NiWS/Al₂₅Zr₇₅ catalyst. A direct correlation was found between high hydrogenation/hydrogenolysis ratio values and low Al₂O₃ concentrations.