Photocatalytic Reduction of Benzophenone on TiO2: Effect of Preparation Method and Reaction Conditions

The photocatalytic reduction of benzophenone was studied focusing on improving the yield to benzhydrol. TiO2 was synthesized by means of a hydrothermal technique. TiO2 (Degussa TiO2-P25) was used as a reference. Catalysts were characterized by XRD and nitrogen physisorption. The photocatalytic reduction was carried out in a batch reactor at 25 degrees C under nitrogen atmosphere, acetonitrile as solvent and isopropanol as electron donor. A 200 W Xe-Hg lamp (lambda = 360 nm) was employed as irradiation source. The chemical composition of the reaction system was determined by HPLC. Structural and textural properties of the synthesized TiO2 depended on the type of acid used during sol formation step. Using HCl, a higher specific surface area and narrower pore size distribution of TiO2 was obtained in comparison with acetic acid. As expected, the photochemical reduction of benzophenone yielded benzopinacol as main product, whereas, benzhydrol is only produced in presence of TiO2 (i.e. photocatalytic route). In general, the hydrothermally synthesized catalysts were less active and with a lower yield to benzhydrol. The optimal reaction conditions to highest values of benzhydrol yield (70-80%) were found at 2 g/L (catalyst loading) and 0.5 mM of initial concentration of benzophenone, using commercial TiO2-P25.