Dynamic studies of the photoinduced metathesis of C3H6 and photoreduction of Mo with CO on anchored and impregnated Mo/SiO2 catalysts

Abstract

Dynamic studies of the photoinduced metathesis of C₃H₆ and the photoreduction of Mo with CO have been performed on two different types of Mo/SiO₂ catalysts containing low Mo contents (0.01–0.1 Mo wt%) but differing in the molybdenum dispersion. The yields of these reactions are higher on anchored than on impregnated Mo/SiO₂ catalysts. Measurements of their relative intensities and lifetimes of phosphorescence indicate that the higher yield of the photoinduced reactions on the anchored catalysts can be attributed to the higher Mo dispersion. The photoinduced metathesis occurs on highly dispersed molybdenum catalysts which contain tetrahedral dioxomolybdenum species. This is in good agreement with ab initio theoretical calculations which predict that molybdenyl species and oxoalkylidene-type carbenes should play a significant role in such a reaction. As for the photoreduction by CO, quantitative measurements of the amount of photoformed CO₂ suggest that the Mo⁶⁺ ions are reduced to the divalent Mo²⁺ state.