Raman spectra of sulfided Mo γ-Al2O3 catalysts were obtained using in situ techniques for two sulfiding methods. For samples sulfided by 10% H2S H2 at 400 °C, MoS2 structures were observed. A stepwise sulfiding using 10% H2S H2, with spectra recorded at 150, 250, and 350 °C, resulted in observation of molybdenum oxysulfide, reduced molybdate, and surface "MoS2" phases. Reexposure of these samples to air led to radical modification of the oxysulfide structures as well as transformation of some sulfide phases. A model incorporating terminal and bridging MoS bonding and anion vacancies is proposed. This model is based on the conversion of isolated and aggregated molybdate and MoO3 species to oxysulfide and reduced molybdenum phases. Conversion of reduced molybdenum phases to sulfides is observed to be slow.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry