Metallo-aerogels derived from chitosan with encapsulated metal nanoparticles as robust, efficient and selective nanocatalysts towards reduction of nitroarenes

A series of robust metallo-aerogels are readily fabricated by pyrolysis of xerogels derived from chitosan-metal (M = Fe, Co, Ni) hydrogels. Owing to the strong coordination between metal ions and the functional groups (NH₂ and OH) of chitosan, metallo-aerogels consisting of encapsulated metal-nanoparticles (MNPs) by graphite shells were obtained, as supported by various characterizations including high-resolution transmission electron microscope (HR-TEM), X-ray diffraction (XRD), and Raman. The resulting metallo-aerogels could be functioned as highly stable, efficient and selective nanocatalysts towards the hydrogenation of nitroarenes to amines at low catalyst loading (1.2 mol.%-2.4 mol.%). Remarkably, the metallo-aerogels could be reused for more than 30 runs without obvious loss of activity and selectivity. These distinguished performances were attributed to the graphitic shells formed during the pyrolysis, which hampered the possible aggregation of MNPs, prevented metal leaching and increased their stability.