Photocatalysed isomerization of butenes on MgO powders with coordinatively unsaturated surface ions

Abstract

The photocatalysed isomerization of but-2-enes has been studied on a standard MgO-I catalyst which exhibits photoluminescence at ca. 340–450 nm associated with coordinatively unsaturated surface ions with 4-coordination. A geometrical isomerization reaction, i.e. trans⇌cis isomerization, occurs predominantly with high efficiency under u.v. irradiation of the MgO catalyst. The excitation wavelength that is effective on the rate of photocatalysed isomerization was found to be in accordance with the photoluminescence excitation spectrum. A complete parallel between the photoluminescence intensity and the rate of photocatalysed isomerization of but-2-enes was also observed. The addition of CO molecules led to the inhibition of the photocatalysed isomerization, its extent increasing with the CO pressure, as well as quenching of the photoluminescence. Stern–Volmer plots for the rate of the photocatalysed isomerization and for the yield of the photoluminescence showed complete agreement. These results clearly indicate that 4-coordinated surface ions play a significant role in the photocatalytic activity of degassed MgO powder catalysts.