Ni and W interactions in the oxide and sulfide states on an Al2O3–TiO2 support and their effects on dibenzothiophene hydrodesulfurization

In order to determine the species distribution at different steps of catalyst preparation, NiW/TiO2–Al2O3 catalysts were prepared by aqueous impregnation with solutions at pH = 4 and 9, respectively. Raman and UV–Vis diffuse reflectance spectroscopies for Ni–W/TiO2–Al2O3 precursors showed that during impregnation step Ni2+Oh–W12O4110− entities were formed for pH = 4 and 9. After calcination, Ni2+Oh/WO42− and Ni2+Oh–W12O4110− species were identified for solids synthesized at pH = 4 and at pH = 9, respectively. Calcined catalyst impregnated at pH 4 displayed the highest Dibenzothiophene (DBT) hydrodesulfurization (HDS) activity for this series. This high activity was related to a higher concentration for the NiWS phase for the catalyst prepared at pH = 4 than that at pH = 9, as evidenced by X-ray photoelectron spectroscopy (XPS). It could be suggested that impregnation at pH = 9 allowed a high Ni–W interaction, forming Ni2+Oh–W12O4110− precursor and consequently, an inefficient sulfidation. Besides, for catalyst impregnated at pH 4, Ni2+Oh/WO42− precursor underwent a more complete transformation to NiWS phase and led to a higher DBT HDS activity.