Photocatalytic Isomerization of Butenes over ZnO and SnO2

It has been found with ZnO as well as TiO2 that 2-butene is much more reactive than 1-butene for their photocatalytic isomerization. Although both cis-trans and double bond isomerizations take place on ZnO, only cis-trans isomerization occurs over SnO2. The photocatalytic isomerizations were suppressed drastically in the presence of NO. From those results together with the ESR studies the following conclusions emerge: a butene molecule interacts with the photoformed O− to form a radical species as a result of fission of the C=C bond; the photocatalytic isomerization proceeds via such a radical intermediate; the lack of the reactivity of 1-butene appears to be explicable on such basis.