Results from the characterization of the NiMo/TNT(x) catalysts
in their oxide state showed that the sodium content in the nanotubular
support strongly affected the type and the proportion of
different Mo oxide species present in the catalyst. On the materials
with high Na loading, a mixture of octahedral and tetrahedral Mo6+
species reducible at temperatures above 500 C was found,
whereas on the low-sodium-content supports, only highly dispersed
and easy-to-reduce octahedral Mo6+ oxide species were
obtained. The presence of tetrahedrally coordinated Mo6+ species
was attributed to the presence of sodium molybdate species
(Na2MoO4 and Na2Mo2O7). Although in the XRD results (Fig. 4)
the formation of these compounds was not observed, probably
because of the small size of the crystallites, it was suspected that
aggregates of these compounds dispersed on the support surface
could be present in the catalysts supported on TNT(x) materials
with high sodium content, which is in line with previous literature
reports [32,58,59,61,62]. The formation of Na2MoO4 and Na2Mo2O7
compounds in Na-doped catalysts was considered to be responsible
for the detrimental effect of sodium because they are difficult
to sulfide and lead to a less active sulfide phase in HDS reactions.
Results from the characterization of the NiMo/TNT(x) catalystsin their oxide state showed that the sodium content in the nanotubularsupport strongly affected the type and the proportion ofdifferent Mo oxide species present in the catalyst. On the materialswith high Na loading, a mixture of octahedral and tetrahedral Mo6+species reducible at temperatures above 500 C was found,whereas on the low-sodium-content supports, only highly dispersedand easy-to-reduce octahedral Mo6+ oxide species wereobtained. The presence of tetrahedrally coordinated Mo6+ specieswas attributed to the presence of sodium molybdate species(Na2MoO4 and Na2Mo2O7). Although in the XRD results (Fig. 4)the formation of these compounds was not observed, probablybecause of the small size of the crystallites, it was suspected thataggregates of these compounds dispersed on the support surfacecould be present in the catalysts supported on TNT(x) materialswith high sodium content, which is in line with previous literaturereports [32,58,59,61,62]. The formation of Na2MoO4 and Na2Mo2O7compounds in Na-doped catalysts was considered to be responsiblefor the detrimental effect of sodium because they are difficultto sulfide and lead to a less active sulfide phase in HDS reactions.
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