Evaluation of the Interest of NiMo Catalysts Supported on MgO–TiO2 for Hydrodesulfurization Applications

Abstract

A series of NiMo catalysts supported on MgO–TiO2 (5 mol% TiO2) were prepared and evaluated in hydrodesulfurization applications. The MgO–TiO2 support was obtained by the sol–gel method. The as-obtained MgO–TiO2 support was then impregnated with nickel nitrate, Ni(NO3)2.6H2O and ammonium heptamolybdate, (NH4)6Mo7O24.4H2O aqueous solutions at pH 9 and pH 5. Subsequently, catalysts were characterized at each step of the preparation: after drying and calcination steps using UV–vis diffuse reflectance (UV–vis-DRS) and Raman spectroscopies and after sulfidation by X-ray photoelectron spectroscopy and transmission electron microscopy. The resulting NiMo catalysts were evaluated in hydrodesulfurization, using thiophene (TP) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) as representative sulfur-containing screening molecules. Finally, catalysts were evaluated in a light cycle oil (LCO) hydrodesulfurization reaction. The pH of the impregnation solution of Ni and Mo precursors influences only slightly the nature of the Ni and Mo species formed. Moreover, in both cases, a significant proportion of nickel is lost into spinel compounds leading to a lower propensity of Ni to be accommodated on the edges of MoS2 slabs decreasing the ability to sulfide correctly the NiMo catalysts. Therefore, MgO appears as a too strong interacting support consuming nickel and forming HDS inactive phases even if the addition of TiO2 tends to enhance textural properties.