Abstract
The photocatalytic dehydrogenation of liquid methanol, ethanol, propan-1-ol and propan-2-ol has been investigated using platinized anatase and 366 nm u.v. radiation over the range 278–303 K. Activities and activation energies for carbonyl-compound formation were effectively identical for the four alcohols on Pt(0.5)/TiO2 prepared by photodeposition. The activation energy of 20 kJ mol–1 is associated with photoelectron transport through the anatase to the Pt particles. With Pt(0.5)/TiO2 prepared by impregnation and H2reduction, identical activities for the four alcohols were achieved after O2 treatment. From the effect of u.v. intensity on the rate of propanone formation at 293 K, the limiting quantum yield was found to be 0.45 for photodeposited Pt(0.5)/TiO2 under N2 and 0.82 for support anatase under O2. Arrhenius plots for reaction at reduced u.v. intensities showed that the activation energy fell to zero when these quantum yields were achieved. Different mechanisms follow from the manner in which photoholes are surface trapped; two mechanisms for dehydrogenation with a limiting quantum yield of 0.5 are discussed.
Published Version
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