ESCA study of "model" allyl-based Mo/SiO₂ catalysts

Stoichiometric redox measurements and X-ray photoelectron spectroscopy (XPS or ESCA) studies were performed on an allyl-based Mo/SiO₂ catalyst (1.7 wt % Mo) obtained by the sublimation of Mo(η³-C₃H₅)₄ onto SiO₂ at 40°C The average oxidation state estimated from stoichiometric measurements correlated well with those reported in the literature. ESCA results indicated that reduction of the Mo/SiO₂ catalyst at 550°C primarily led to the formation of Mo²⁺. Also, the results were consistent the reported reversibility of the redox cycle. However, the reported formation of discrete Mo⁴⁺ by oxidation of the reduced catalyst at room temperature could not be substantiated.