Titania nanotubes were synthesized by hydrothermal treatment of a titania precursor with 10 M NaOH
followed by ion exchange with hydrochloric acid and used as supports for NiMo hydrodesulfurization
(HDS) catalysts. Titania nanotubes prepared in this manner always contain a certain amount of residual
sodium in their structure. The aim of the present work was to inquire into the effect of the sodium content
in the titania nanotubes on the characteristics of the deposited Ni and Mo species and on their performance
in HDS of dibenzothiophene. Results from the characterization of the prepared NiMo catalysts
showed that the sodium content in the nanotubes is an important factor that has a strong influence on
the coordination state of the supported Mo6+ oxide species and the ease of their reduction, as well as
on the morphology of the MoS2 active phase and the relative proportion of the coordinatively unsaturated
active sites (CUS) and fully sulfided MoS2 species. A clear relationship was observed between the sodium
content in the titania nanotubes and the activity and selectivity trends of the NiMo catalysts in
hydrodesulfurization. Catalysts supported on titania nanotubes with high Na content showed low catalytic
activity, but high selectivity toward the direct desulfurization of dibenzothiophene, which was
attributed to the presence of a considerable number of CUS sites. In contrast, the NiMo catalysts supported
on titania nanotubes with low Na content that resulted in their being active in the HDS of dibenzothiophene
had principally fully sulfided MoS2 species and showed high hydrogenation ability.