Addition of Cerium to Alumina-Supported NiMo Catalysts for Dibenzothiophene Hydrodesulfurization Application

In the present study, the influence of adding cerium oxide to NiMo/Al2O3 hydrodesulfurization (HDS) catalysts was herein analyzed through the impregnation of cerium sulfate at the surface of an Al2O3 support obtained by a sol–gel method at two different Ce contents (1 and 5 mol% as CeO2). The cerium-containing Al2O3 supports were then impregnated with Ni(NO3)2 and (NH4)6Mo7O24 precursors in aqueous solutions at pH 7 or pH 9 before being dried at 120 °C for 4 h and finally calcined under air at 400 °C for 4 h. The as-obtained NiMo/Ce–Al2O3 catalysts were characterized at their oxide state using UV–Vis diffuse reflectance, Raman and Infrared spectroscopies after each preparation step. Catalysts were also characterized at the sulfide state by pyridine adsorption followed by infrared spectroscopy. The sulfide catalysts were then evaluated in the hydrodesulfurization of dibenzothiophene (DBT). Results show that the pH of impregnation used influences more the final HDS activity than the amount of Ce with an optimum observed using 1 mol % and a pH of impregnation of 9. The activity achieved is then 62% higher than for a NiMo/Al2O3 reference catalyst. The analysis of both Raman and UV–Vis spectroscopy results show that impregnation under basic conditions help to maximize the dispersion of the CeO2 phase onto the alumina support improving substantially the final HDS activity.