Modulating the Electronic Structure of α-Fe2O3 by Doping Atomically Dispersed Ce for the Transfer Hydrogenation of Nitroaromatics Using Stoichiometric Hydrazine Hydrate

Abstract

The metal-oxide-catalyzed transfer hydrogenation of nitroarenes to anilines by hydrazine hydrate has been widely reported; however, the risk of explosion resulting from excess hydrazine hydrate and high temperatures and complex preparations of these catalysts immensely hinder their industrial application. Herein, we use a simple co-precipitation method to synthesize atomically dispersed Ce-doped α-Fe2O3 (Ce0.025-Fe2O3-350 °C), which can completely reduce nitroarenes using stoichiometric hydrazine hydrate at room temperature, where the parent α-Fe2O3 is inactive. A thorough characterization indicates that the incorporation of Ce into the crystal lattice of α-Fe2O3 reorganizes the electronic structure of the surrounding Fe, such that the Lewis acidity of Fe2O3 is enhanced, which is the key for the room-temperature decomposition of N2H4·H2O. The structure is also beneficial for the adsorption of nitroarene, leading to the weakening of the N–O bonds. Mechanistic experiments and DFT calculations demonstrate that the reduction proceeds through Ph-NO2 → Ph-NHOH → Ph-NH2 without the widely recognized Ph-NO intermediate. Moreover, Ce0.025-Fe2O3-350 °C exhibits good stability in a continuous-flow reaction.