Abstract
AbstractThe effects of reduction, evacuation and adsorbate adsorption on Mo/SiO2 catalysts prepared by impregnation were studied by means of the electron paramagnetic resonance (EPR) technique. Pentavalent molybdenum species in the overlayer (Mo05+, g⟂ = 1.941, g| = 1.895) and at the interface (Moi5+, g⟂ = 1.952, g| = 1.866) between MoO3 and SiO2 were distinguished in the EPR spectra; they were observed from samples reduced at T < 573 K and T > 573 K respectively. The difference in their nature reflected the extent of their interaction with the support. Mo05+ existed in the MoO3 overlayer of the catalyst and interacted only weakly with the support. Moi5+ from the Mo ions connected directly to SiO2 was affected strongly by the support. The anisotropic factor of the measured Moi5+ signals increased with the extent of support interaction.Superoxide ions (O2, g1 = 2.016, g2 = 2.011, g3 = 2.006) were found upon oxygen adsorption on samples evacuated at temperatures above 573 K. The observed O2 may exist at the interface between MoO3 and the support.
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