Abstract:
In-situ EXAFS studies of sulphided Mo/TiO2 catalysts have shown that at low Mo loadings (2–4 wt%), an active species with a short Mo-S distance of 2.25 Å is formed, while on Mo/TiO2 with high Mo loadings as well as on Mo/γ-Al2O3, bulk MoS2 (Mo-S, 2.42 Å) is formed. The species with the short Mo-S distance has Mo in an oxidation state close to 6+ and is likely to result from the sulphidation of the tetrahedral molybdate species present in the oxidic precursor at low Mo loadings. The calcination temperature of the oxidic precursor appears crucial, a high calcination temperature of 973K favouring the formation of MoS3 on sulphidation, and a low calcination temperature of 623K favouring MoS2.
