Photoreducibility of [formula omitted] catalysts with CO

Abstract

The photoreduction of supported Mo SiO 2 catalysts by CO has been investigated at room temperature as a function of Mo coverage and wavelength of the incident UV irradiation. The CO adsorbed on photoreduced Mo ions has been investigated by IR spectroscopy. In the literature, it has been reported that CO photoreduction of Mo SiO 2 catalysts leads to the formation of Mo 4+ and Mo 5+ ions. Results of this study indicate that CO photoreduction also leads to the formation of Mo ions in valence states lower than Mo 4+. In particular, the pairs of IR bands observed at 2100, 2135 cm −1 and 2075, 2125 cm −1 were attributed to pairs of CO molecules adsorbed on Mo 4+ or Mo 3+, and Mo 2+ sites, respectively. These sites are assumed to be formed from the CO photoreduction of dimeric surface molybdates. Another IR band observed at 2035 cm −1 may be attributed to the stretching vibrations of a CO molecule adsorbed in a bridged configuration between two adjoining Mo 2+ or to a single CO adsorbed linearly on Mo 2+ sites. Thus, our results indicate that the low-temperature CO photoreduction is a complex process and that Mo ions in several valence and coordination states may be formed simultaneously during CO photoreduction in Mo SiO 2 catalysts.