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 (lambda >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.