Adsorptive and Kinetic Properties on Photocatalytic Hydrogenation of Aromatic Ketones upon UV Irradiated Polycrystalline Titanium Dioxide: Differences between Acetophenone and Its Trifluoromethylated Derivative

Adsorptive and kinetic properties on photocatalytic hydrogenation of acetophenone (AP) and 2,2,2-trifluoroacetophenone (TFAP) have been investigated upon UV irradiated P25 TiO2 in deaerated ethanol. Kinetic, data of An were analyzed by the Langmuir-Hinschelwood kinetic expression, -dCs/dt = k(max)K(irr)Cs/(1 + AK(irr)Cs), where k(max) is the maximum rate and K-irr is the apparent adsorption constant under the irradiation. The hydrogenation of AP proceeded in the light limited controlled manner, in which k(max) increased with increasing light intensity. The hydrogenation of TFAP exhibited first-order kinetics due to the predominant formation of ketal in ethanol. Electron transfer efficiency from conduction band and/or electron trap sites on TiO2 to AP or TFAP was also evaluated. In the case of AP, ca. 75% electrons trapped at relative shallow sites were able to transfer into AP, whereas ca. 25% ones trapped at deep sites remained on the TiO2 surface. For TFAP, all of the trapped electrons transferred into TFAP. Reaction models to account for these experimental results are proposed and discussed in detail.