Photocatalyzed Isomerization of Butenes over Metal Sulfides. High Photocatalytic Activity and Its Origin

Article abstract of DOI:10.1246/bcsj.59.3765

Photocatalytic activity of CdS and ZnS for the cis-trans isomerization of 2-butene is much higher than that of TiO2 and ZnO, though the double bond shift isomerization to 1-butene hardly proceeds in contrast with the case of the oxides.The addition of O2 or NO molecules leads to the remarkable inhibition of photocatalyzed isomerization.From these results together with the ESR measurements before and after UV irradiation of the sulfide catalyst either in the presence or in the absence of butene, the following conclusions emerge: sulfur radicals such as S_n, which are produced by the hole trapping by lattice S^2- ions and/or sulfur clusters existing in the catalyst inherently, play a significant role in the weakening of the C=C double bond of 2-butene via the interaction with the molecules; the stability of such sulfur radicals results in the much higher photocatalytic activity of CdS and ZnS catalysts as compared with that of metal oxide catalysts.