XPS of the Surface Species in Sulfided Mo-K-Rh/Al₂O₃ Catalysts

The surface Mo,S and Rh species in the sulfided Mo-K-Rh/Al₂O₃ catalysts with variable Rh contents were investigated by XPS.From their analyses of the fitting results of the XPS spectra,it was found that the Mo species in the catalysts are MoS₂,MoS_2+x in the sulfur-enriched species and Mo⁵⁺ and Mo⁶⁺ .The S in the catalysts can take the forms of S⁶⁺ ,S⁰ or Sn,S^2- and （S-S）^2- in the sulfur-enriched species.With the increase of the Rh content in the catalysts,the surface concentrations of MoS_2+x ,Mo⁶⁺ ,S₂^2- and S⁶⁺ decrease,while those of Mo 4+ ,Mo₅₊ ,S^2- and S⁰ increase to some extent indicating that the addition of Rh in the catalysts promotes the sulfidation of molybdena.Because of the interaction with the Mo component,the Rh species could be existed not only as Rh⁰,but also as Rhⁿ⁺ （n=1,2 and 3） which is most probably responsible for the improved properties of the catalysts for alcohol synthesis from syngas.