Abstract
Structures formed from molybdenum supported on planar SiO 2 under oxidizing, reducing, sulfiding and carbiding conditions are studied using transmission electron microscopy and X-ray photoelectron spectroscopy to characterize structures which should form in Mo/SiO 2 catalysts. Oxidized 10 Å Mo films form disordered Mo +6 oxides with particle sizes <20 Å for all treatment temperatures. Both Mo films and sintered Mo particles > 300 Å diameter form crystalline MoO 3 upon treatment in O 2. Mo films and particles are converted completely to MoS 2 upon heating metal or oxide to 350°C in H 2S/H 2. Dispersion of Mo is only altered significantly under reducing and carbide forming conditions above 500 °C and during oxidation of MoS 2 films above 300 °C. Redispersion of sintered catalysts through oxidation did not occur, although regeneration of sulfided and carbide catalysts was possible through controlled oxidation. Alkali contaminants in the SiO 2 substrate strongly influence the molybdenum dispersion.
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