H. Courbon, J. Herrmann, P. Pichat
Nov 1, 1981
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0
Influential Citations
39
Citations
Journal
Journal of Catalysis
Abstract
Cyclopentane-deuterium isotopic exchange (CDIE) was performed at −10 °C with a C5H10D2 ratio of ∼-6.4% over an illuminated (300–410 nm) 0.5 wt% Pt/anatase catalyst. A selectivity in C5H9D of ∼-90% was found with a total quantum yield of ∼-1.8%. The photocatalytic nature of CDIE under these conditions was established from these results: (i) no CDIE in the absence of photons of wavelengths shorter than the absorption edge of anatase or when TiO2 was replaced by SiO2, whereas the CDIE observed at higher temperatures (from 0 °C) without uv light mainly produced multiply exchanged cyclopentane, (ii) a linear CDIE rate-illumination time relationship was found, and (iii) an experiment carried out with the same catalyst sample showed that it was capable of exchanging, in successive runs, without decrease in activity, an amount of C5H10 78 times greater than that corresponding to a photoinduced stoichiometric surface reaction. By contrast, CDIE over pure TiO2 was limited and was only observed for hydroxylated specimens pretreated in D2 at 300 °C. It is concluded that (i) CDIE occurred on anatase between weakly adsorbed C5H10 and OD− ions activated by the trapping of photoproduced positive holes, and (ii) Pt, besides attracting the support-free electrons which decreased the recombination of electron-hole pairs, regenerated the titania OD− ions after their isotopic exchange, which involved D2 dissociative adsorption on the metal and subsequent migration of D atoms to the oxide. This constitutes an example of bifunctional heterogeneous photocatalysis.