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 TiO 2 in deaerated ethanol. Kinetic data of AP were analyzed by the Langmuir–Hinschelwood kinetic expression, −d Cs /d t = 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 TiO 2 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 TiO 2 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.