Both types of sites detected in our sulfided catalysts by FT-IR of
adsorbed CO are important for HDS reactions. It is generally
believed that vacant (CUS) sites are responsible for S removal
through the direct desulfurization pathway (DDS), whereas the
hydrogenation route (HYD) may be catalyzed by a fully sulfided
MoS2 system, where the ‘‘metallic brim’’ can be formed on the
MoS2 basal plane [51,63–66]. From this point of view, the changes
in the proportion of saturated and unsaturated sites in our catalysts
supported on TNT(x) materials with different Na+ loading
(FT-IR of adsorbed CO) are in line with the modifications in the
selectivity patterns of the catalysts as a function of their sodium
content. The NiMo/TNT(7.1) catalyst with the largest number of
CUS sites showed the highest hydrogenolysis ability (Table 5),
whereas the NiMo/TNT(0.1) sample, in which the fully sulfided
MoS2 phase was predominant, resulted in the highest HYD ability.
The difference in the selectivity of these two catalysts was big
enough (about 15 times), which can be attributed, on one hand,
to the changes in the morphology of the sulfided MoS2 phase,
and, on the other hand, to modification in the type and characteristics
of the active sites, as described above.