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

Abstract

We report that photoactivated rutile titanium dioxide (TiO 2 ) catalyzes a highly efficient and selective hydrogenation of nitroaromatics with alcohol as a hydrogen source. Photoirradiation (λ >300 nm) of rutile TiO 2 suspended in alcohol containing nitroaromatics at room temperature and atmospheric pressure produces the corresponding anilines with almost quantitative yields, whereas common anatase and P25 TiO 2 show poor activity and selectivity. The Ti 3+ 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-toamine hydrogenation of the adsorbed nitroaromatics by the surface-trapped electrons, enabling aniline formation with significantly high quantum yields (>25% at <370 nm). The rutile TiO 2 system also facilitates chemoselective hydrogenation of nitroaromatics with reducible substituents; several kinds of functionalized anilines are successfully produced with >94% yields.

Reactivity of Trapped and Accumulated Electrons in Titanium Dioxide Photocatalysis

“…Shiraishi et al reported that some kinds of rutile TiO 2 particles promote the highly efficient photocatalytic hydrogenation of nitroaromatic compounds [81,82]. They claimed that the oxygen vacancy sites on the rutile {110} behave as the adsorption sites for the nitroaromatic compounds and the electron trap sites, resulting in the formation of aniline derivatives with significantly high yields of greater than 25% at 370 nm [81].…”

“…They claimed that the oxygen vacancy sites on the rutile {110} behave as the adsorption sites for the nitroaromatic compounds and the electron trap sites, resulting in the formation of aniline derivatives with significantly high yields of greater than 25% at 370 nm [81]. They also found that the activity of rutile particles depends on the number of defects on the particles [82].…”

“…For example, molecular oxygen (O 2 ) in a gaseous phase would be easily adsorbed on the surface Ti ds and reduced by electrons Ti ds 3+ and e cb − , resulting in the efficient formation of ROS, which oxidize benzene efficiently [16]. Further, the surface Ti ds behaves as the active reaction site in the efficient reduction of nitrobenzene [81]. Thus, the surface defects favorably act as adsorption sites as well as reaction sites.…”

Transformation of polymer-ZnO core–shell nanofibers into ZnO hollow nanofibers: Intrinsic defect reorganization in ZnO and its influence on the photocatalysis

“…Ever increasing environmental pollution forces the researchers to fabricate efficient catalysts which can use sunlight to disintegrate or oxidize the organic substances [1][2][3][4][5][6][7][8][9][10][11][12][13][14]. It is known that delaying the recombination of photogenerated electron-hole pair increases the efficiency of the catalysts [10,12,[15][16][17][18][19][20][21][22][23].…”

“…It is known that delaying the recombination of photogenerated electron-hole pair increases the efficiency of the catalysts [10,12,[15][16][17][18][19][20][21][22][23]. On the other hand, the efficiency of the catalyst is dependent on the crystal-phase [1,3]. i.e., the formation of • OH radical [12][13][14] depends on the crystalline facets those were exposed.…”