Photocatalytic dehydrogenation of liquid alcohols by platinized anatase

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.