Influence of Na content on behavior of NiMo catalysts supported on titania nanotubes in hydrodesulfurization

• NiMo catalysts supported on titania nanotubes with different Na content were studied.
• Catalytic activity was tested in dibenzothiophene hydrodesulfurization.
• Effect of the support’s Na content on HDS activity and selectivity was observed.
• High-Na content TNT resulted in low active catalysts, highly selective for the DDS.
• Low-Na content nanotubes resulted in active NiMo catalysts with high HYD ability.

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.

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