Cerium(iv) oxide as a novel candidate material for time-separated redox reaction using photocatalytically accumulated electrons

Abstract

The time separation of redox reactions is a novel strategy to retard the back reaction and/or side reactions in photocatalytic organic transformation systems. In the present study, potential materials among several metal oxide photocatalysts were explored for a time-separated redox reaction, and cerium(IV) oxide (CeO₂) was found to show the selective hydrogenation of nitrobenzene to aniline. Moreover, the hydrothermally synthesized CeO₂ (hs-CeO₂) exhibits the best hydrogenation performance, with a conversion rate and selectivity both over 99%, as well as excellent cycle stability. The reaction with hs-CeO₂ was also applicable to the chemoselective reduction of nitro compounds with some functional groups, and the selectivity was much higher than that of conventional photocatalytic reactions. This is presumably because only the reduction of nitro compounds by accumulated electrons proceeds without photoexcitation in the dark phase of the time-separated reaction.