HDS and HDN activity of (Ni,Co)Mo binary and ternary nitrides prepared by decomposition of hexamethylenetetramine complexes

Highly dispersed pure phases of binary and ternary nitrides (Co,Ni)Mo were prepared using decomposition of hexamethylenetetramine (HMTA) complexes. Their catalytic activity was evaluated in the HDS of thiophene and HDN of quinoline. Three different pre-treatment modes were applied, including direct in situ preparation of nitrides in the catalytic reactor; pre-sulfidation with hydrogen sulfide and soft oxidation in air followed by sulfidation. Pure bimetallic nitrides are highly active HDN catalysts in the absence of sulfur and show substantial synergy effect between Ni or Co and Mo. By contrast, no synergy was observed for thiophene HDS, specific surface rates for binary and ternary nitrides being similar to that of unsupported MoS2. Transmission microscopy, XRD and XPS studies showed that MoS2 segregation on the surface occurs during HDS reaction or sulfidation with H2S. As a result bimetallic catalysts contained nitride particles covered with MoS2 layers and VIII group metal sulfide crystalline particles in the subsurface layer. The introduction in the preparation sequence of an additional step of oxidation–sulfidation led to a considerable increase of HDS catalytic activity of bimetallic catalysts. Pre-sulfidation of nitrides with H2S/H2 mixture resulted in a drastic decrease of specific surface area (Ssp) and very low HDS activity. Soft sulfidation with thiophene under reaction conditions led to high Ssp and high HDS activity per unit of mass.

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► Highly dispersed Mo2N, Co3Mo3N and Ni3Mo2N were prepared from HMTA complexes.
► Co(Ni)Mo nitrides are highly active HDN catalysts in the absence of sulfur.
► Sulfidation leads to surface segregation of MoS2 and loss of activity.
► Soft oxidation and resulfidation allows partial recovery of CoMoS phase.