Sulfiding of cobalt molybdate catalysts: Characterization by Raman spectroscopy

In situ laser Raman spectroscopic studies of the sulfiding of cobalt molybdate hydrodesulfurization catalysts were performed. Sulfiding in 10% H₂S H₂ at 400 °C resulted in the formation of stable MoS₂ structures after 2 h. However, the Raman spectra indicated that small crystallites or surface layers of perhaps distorted MoS₂ were present. Stepwise sulfiding of samples to 150, 250, and 350 °C permitted intermediate stages of sulfiding to be examined. Differences were observed for the relative rates of reduction versus sulfur incorporation for CoMoO₄, Co₃O₄, MoO₃, and aggregated or polymeric molybdate phases. Cobalt tended to increase the extent of reduction of the catalyst. A previously described model is extended to include the role of cobalt.