Chemoselective hydrogenation of nitroarenes: Boosting nanoparticle efficiency by confinement within highly porous polymeric framework

We report for the first time 99.9% yield of aminocompounds and high TOFs (up to 61 s(-1)) in the liquid-phase hydrogenation of several para-substituted (-OH, -OCH3, -CH3, -H, -Br, -Cl, -COOH and -NO2) nitroaromatics over quasi-monodispersed (ca. 3.3 nm from microscopy and CO chemisorption) Pt nanoparticles (NPs) confined within a hyper cross-linked polystyrene (HPS) polymeric matrix (uniform pore size similar to 4.6 nm; 1065 m(2) g(-1)). Taking the selective hydrogenation of p-chloronitrobenzene as a model reaction, an antipathetic structure sensitivity (i.e. up to a 3-fold TOF greater over larger, 1.6 -> 3.3 nm, Pt NPs) has been established. Moreover, a higher activity and amine selectivity were attained at elevated pressures (1 -> 20 bar) irrespective of the support (i.e. active carbon, Al2O3 and HPS). Nonetheless, while Pt/HPS shows high stability without any activity/selectivity loss in repeated reaction runs, the state-of-the-art active carbon and alumina-supported Pt catalysts underwent a decrease in activity as a result of metal leaching. Our results demonstrate the potential of HPS as a suitable support for tailoring metal nanoparticle size and circumvent undesirable metal leaching. (C) 2013 Elsevier Inc. All rights reserved.