Nickel molybdate as precursor of HDS catalysts: Effect of phase composition

Sulfided αand β-NiMoO₄ have been employed as model HDS catalysts, aiming to investigate the effect of phase composition of the precursor mixed oxide on the physicochemical characteristics and activity of the sulfides. Both sulfides are highly amorphous or microcrystalline, and could not be differentiated by means of XRD. The differences in BET area were also found to be minimal. However, it was found by means of TPR that the stable α-isomorph is reduced at lower temperatures than the unstable β-phase in both the oxidic and sulfided states. Sulfided β-NiMoO₄ was found to be a better catalyst for the HDS of thiophene than the sulfided α-isomorph. This could be related to the higher stability of the former in H₂, as decomposition of the active, amorphous Ni-Mo-S structures results in less active and more crystalline phases, as found by XRD.