Hydrogenation of nitrobenzenes catalyzed by platinum nanoparticle core-polyaryl ether trisacetic acid ammonium chloride dendrimer shell nanocomposite

Platinum nanoparticle core-polyaryl ether trisacetic acid ammonium chloride dendrimer shell nanocomposites (Pt@G(n)-NACl) were prepared and used as catalysts for hydrogenation of nitrobenzenes to anilines with molecular hydrogen under mild conditions. The as-prepared nanoparticles have mean particle size from 2.0 to 5.5 run, depending on the molar ratio of the metal and the dendrimer. The Pt nanoparticles demonstrate near-monodisperse when the molar ratio of Pt and G(3)-NACl is below 30. The interaction among three carboxyl groups terminated at the dendron and the metallic core keeps the Pt nanoparticles from agglomerating. The colloidal solution of Pt nanoparticles stabilized by the dendrimer, in which the molar ratio of Pt/G(3)-NACl was less than 60, is stable without precipitation for several weeks. The dendrons attach to the metal core radially, and a substantial fraction of the surface of the metal nanoparticle is unpassivated and available for catalytic reactions. Turnover frequencies for the hydrogenation of nitrobenzenes to anilines change from 353 to 49 h(-1) depending on the dendrimer generation and substrates. The dendrimer catalysts are stable during the catalytic hydrogenation process and can be recovered by centrifugation and reused. The results suggest the effectiveness of polyaryl ether trisacetic acid ammonium chloride dendrimer as a stabilizer for the preparation of Pt nanoparticle catalysts. (c) 2006 Elsevier B.V. All rights reserved.