Abstract

The secondary alcohols, propan-2-ol and butan-2-ol, and also the tertiary alcohol 2-methyl-propan-2-ol are shown to undergo selective photo-oxidation over rutile surfaces, when exposed to u.v.-illumination in the presence of gaseous oxygen. Gaseous oxygen labelled with oxygen-18 experienced a rapid photoinitiated depletion from the gas phase over these (alcohol +18O2)/TiO*2 interfaces but very little oxygen-18 label was incorporated into the ketone products of selective photo-oxidation over pure TiO2. Photo-oxidation of an oxygen-18 labelled sample of the tertiary alcohol over preoxidised rutile in the presence of 16O2 resulted in almost total loss of the oxygen-18 label from the acetone product of photo-oxidation. Over prereduced rutile surfaces, however, photo-oxidation was much slower and the acetone photoproduct contained the same percentage of oxygen-18 as the parent alcohol. The mechanisms developed to account for these results assign an important role to hole-trapping at coordinatively unsaturated O2– sites on the rutile surface and envisage large differences in ease of detachment of such lattice oxygen species from preoxidised and prereduced surfaces of pure TiO2.

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