Photocatalytic Hydrogenation of CH3CCH with H2O on Small-Particle TiO2: Size Quantization Effects and Reaction Intermediates

Article abstract of DOI:10.1021/j100300a021

Photocatalytic hydrogenation reactions of CH3CCH with H2O were investigated with TiO2 catalysts of extremely small particle size.Photocatalytic activity increased as the diameter of the TiO2 particles becomes smaller, especially below 100 Angstroem.Absorption and photoluminescence spectra of catalysts exhibit blue shifts as the diameter of TiO2 becomes smaller, also especially below 100-Angstroem particle size, suggesting that a size quantization effect is operating.Photoformed, carbon-centered radical species resulting from the fission of the carbon-carbon bond of alkyne molecules and Ti³⁺ ions as trapped electrons were directly observable.The different dependence of the yields on the particle diameter of TiO2 catalyst suggests that the differences in photocatalytic activity arise from the differences in the reactivity but not in the physical properties such as the surface area of these catalysts.This demonstrates a size quantization effect at extremely small TiO2 particles.Reduction of size might result in some electronic modification of TiO2 to produce an enhancement of the activities of electrons and holes, and/or a suppression of the radiationless transfer of absorbed photon energies.