Photocatalytic Hydrogenation of Alkynes and Alkenes with Water over TiO2. Pt-Loading Effect on the Primary Processes

Article abstract of DOI:10.1021/j150662a027

Photoreactions of alkynes and alkenes with water have been investigated over Pt-loaded and unloaded TiO2 in order to obtain information about the effects of Pt loading on photocatalytic reactions.With unloaded TiO2, the major photoformed products are those formed by the hydrogenation accompanied by the fission of the C<*>C and C=C bond of the reactants, while with Pt-loaded TiO2, i.e., Pt/TiO2, a significant enhancement of hydrogenation reaction without the bond fission is observed.In addition to those products, oxidation products such as CO and CO2 are found.In contrast to the features with unloaded TiO2, with Pt/TiO2 there is no marked difference between the yields of the oxidation and reduction products.ESR measurements show that photoformed electrons are accumulated as localized Ti³⁺ ions with unloaded TiO2, whereas with Pt/TiO2 electrons are easily transferred from TiO2 to Pt particles.From these results and those of kinetic studies the significance of the close existence of electrons and holes for unloaded TiO2 proposed in the preceding paper is confirmed.Furthermore, it has been shown that with Pt/TiO2 a photoelectrochemical process is predominant, the reduction of H⁺ on Pt particles and the oxidation by ^.OH on TiO2 bringing about photohydrogenation without bond fission and formation of oxidation products, respectively.