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 °C under nitrogen atmosphere, acetonitrile as solvent and isopropanol as electron donor. A 200 W Xe-Hg lamp (λ = 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.