Exotic Nanostructured Titania Supports for Deep Hydrodesulfurization Catalysts: Are They Better Than the Conventional Ones?

Abstract

In the present work, we compared the hydrodesulfurization (HDS) behavior of NiMo catalysts supported on titania-based nanomaterials (hydrogen titanate nanotubes and nanotubes decorated with anatase nanocrystals), with that of the reference NiMo/γ-alumina and NiMo/TiO2 samples. Supports and calcined catalysts were characterized by nitrogen physisorption, powder XRD, UV–Vis diffuse reflectance spectroscopy, Raman spectroscopy, temperature-programmed reduction, scanning electron microscopy and high resolution transmission electron microscopy (HRTEM). The sulfided catalysts were characterized by HRTEM and evaluated in the HDS of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT). In the hydrodesulfurization of DBT, all catalysts supported on nanostructured titania materials showed similar activity as the NiMo/Al2O3 reference. However, their selectivity towards the hydrogenation pathway of the reaction was significantly higher than that of the alumina-supported reference. In the hydrodesulfurization of 4,6-DMDBT, activities of the synthesized NiMo catalysts supported on titania-based nanomaterials were about 50% superior to that of the NiMo/Al2O3 reference. This is an interesting result, since the majority of the conventional NiMo or CoMo catalysts are significantly more active for the elimination of DBT than of the sterically-hindered 4,6-DMDBT. The presence of small titania anatase crystallites in the nanostructured supports had a slight positive effect on the catalytic activity of the NiMo catalysts in HDS of 4,6-DMDBT, and a more noticeable effect on an increase in their hydrogenation ability (production of larger amounts of methylcyclohexyltoluene in the products).