Rutile Crystallites Isolated from Degussa (Evonik) P25 TiO₂: Highly Efficient Photocatalyst for Chemoselective Hydrogenation of Nitroaromatics

We report that the rutile crystallites, isolated from Degussa (Evonik) P25 TiO₂ by a hydrofluoric acid treatment, behave as a highly efficient photocatalyst for hydrogenation of nitroaromatics. Photoirradiation (λ >300 nm) of the isolated rutile particles with alcohol as a hydrogen source successfully promotes chemoselective hydrogenation of nitroaromatics to anilines, with an activity higher than that of commercially available rutile TiO₂. The high activity of the isolated rutile particles is due to the specific distribution of structural defects (oxygen vacancy sites) on the particles. These particles contain a relatively small number of inner defects behaving as recombination centers for photoformed electron (e^–) and positive hole (h⁺) pairs, and a relatively large number of surface defects behaving as reduction sites for nitroaromatics. Photoexcitation of the isolated particles therefore promotes efficient charge separation between e^– and h⁺, and facilitates rapid reduction of nitroaromatics adsorbed on the surface defects. This thus results in very high hydrogenation activity on the rutile particles isolated from P25 TiO₂.