Efficient and chemoselective hydrogenation of nitroarenes by γ-Fe2O3 modified hollow mesoporous carbon microspheres

Recently, it has become imperative to design non-precious-metal-based nanocatalysts with high catalytic efficiency for the hydrogenation of nitroarenes to the corresponding aromatic amines under mild reaction conditions. In this study, γ-Fe2O3-nanoparticle-supported hollow mesoporous carbon microsphere (h-MCM) nanocatalysts (γ-Fe2O3/h-MCM) were prepared, and their catalytic performance for the hydrogenation of nitroarenes was investigated. Here, h-MCM prepared by the co-sol–emulsion-gel method exhibited a mesoporous hollow structure, high surface area, and accessible interior space as well as a graphitic carbon framework; thus, aromatic compounds can sufficiently come into contact with the active sites, as well as enhance the mass transfer effect. N2H4·H2O used herein as the reducing agent only generated N2 and H2O as harmless by-products. γ-Fe2O3/h-MCM was obtained by the calcination of Fe(NO3)3-absorbed h-MCM under an inert atmosphere. From transmission electron microscopy results, the annealing temperature significantly affected the γ-Fe2O3 particle size, and in turn catalytic activity: the γ-Fe2O3/h-MCM nanocatalyst annealed at 500 °C for 15 min (20%-γ-Fe2O3/h-MCM-500-15) exhibited high catalytic activity. By the use of 20%-γ-Fe2O3/h-MCM-500-15 as the optimal catalyst, all nitroarenes investigated for hydrogenation exhibited high conversion, with a 100% selectivity for aniline, indicating the excellent selectivity of γ-Fe2O3-based catalysts. In addition, the catalyst can be easily recovered with an external magnetic field and reused at least five times without obvious decrease in catalytic activity. This study provides a useful platform based on a cost-effective, magnetically recyclable γ-Fe2O3-based nanocatalyst for the highly efficient hydrogenation of nitroarenes.