Citric acid loading for MoS2-based catalysts supported on SBA-15. New catalytic materials with high hydrogenolysis ability in hydrodesulfurization

Abstract

The aim of this work is to get a deeper insight into the effect of citric acid (CA) loading in NiMo sulfided catalysts supported on SBA-15 on their behavior in hydrodesulfurization (HDS). Catalysts were prepared by simultaneous impregnation of Ni, Mo and CA species, varying the CA amount in aqueous solution. After the impregnation, NiMoCA catalysts were dried at 100°C under air atmosphere without calcination. Catalysts were characterized by several techniques (TGA, N2 physisorption, small-angle and powder XRD, FT-IR, UV–vis DRS, TPR, elemental analysis and HRTEM) and tested in HDS of dibenzothiophene (DBT). N2 physisorption, small-angle XRD and FT-IR showed the adsorption of CA on the SBA-15 surface. XRD characterization demonstrated that Ni and Mo oxide species were well dispersed in all catalysts. UV–vis DRS revealed better dispersion of Mo species with the increase of CA loading. TPR experiments exhibited an important effect of CA under reducing atmosphere; it can be reduced to leave carbon on the catalytic materials. This observation was confirmed by carbon analysis which showed an increase in the amount of carbon in the same direction than the CA loading. HDS of DBT showed differences in activity and selectivity of the catalysts prepared with different CA loading. We observed outstanding promotion of direct desulfurization (DDS) route with increasing the CA amount. The preference of DBT to react over NiMoCA catalysts toward DDS route was an unexpected behavior.