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

Abstract

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.