Highly Efficient and Selective Hydrogenation of Nitroaromatics on Photoactivated Rutile Titanium Dioxide

We report that photoactivated rutile titanium dioxide (TiO2) catalyzes a highly efficient and selective hydrogenation of nitroaromatics with alcohol as a hydrogen source. Photoirradiation (lambda > 300 nm) of rutile TiO2 suspended in alcohol containing nitroaromatics at room temperature and atmospheric pressure produces the corresponding anilines with almost quantitative yields, whereas common anatase and P25 TiO2 show poor activity and selectivity. The Ti3+ atoms located at the oxygen vacancies on the rutile surface behave as the adsorption site for nitroaromatics and the trapping site for photoformed conduction band electrons. These effects facilitate rapid and selective nitro-to-amine hydrogenation of the adsorbed nitroaromatics by the surface-trapped electrons, enabling aniline formation with significantly high quantum yields (>25% at <370 nm). The rutile TiO2 system also facilitates chemoselective hydrogenation of nitroaromatics with reducible substituents; several kinds of functionalized anilines are successfully produced with >94% yields.