Photocatalytic dehydrogenation of aliphatic alcohols by aqueous suspensions of platinized titanium dioxide

Abstract

Photoirradiation (λ_ex > 300 nm) of Ar-purged aqueous propan-2-ol solution gave hydrogen and acetone in the presence of platinum- and/or ruthenium dioxide-loaded TiO₂. The photocatalytic activity of anatase TiO₂ depended significantly on the amount of metal or metal oxide present; the effect on the activity increased in the order platinum black ≫ platinum powder > ruthenium dioxide. The photocatalytic activity of rutile TiO₂ was negligible even when loaded with platinum black. The effective wavelengths for the photocatalytic dehydrogenation of propan-2-ol were below ca. 390 nm, in agreement with the u.v. absorption spectrum of anatase TiO₂. In a similar way primary, secondary and tertiary aliphatic alcohols underwent photocatalytic oxidation, accompanied by hydrogen liberation, by the platinized TiO₂. The primary and secondary alcohols gave the corresponding carbonyl derivatives, while 2-methylpropan-2-ol and acetone gave dimeric products accompanied by stoichiometric hydrogen evolution. The initial rate of dehydrogenation in these photocatalytic systems was in proportion to the rate constants of hydrogen abstraction by hydroxyl radical in the homogeneous systems.