ABSTRACT
Department of Chemistry, Trinity University, One Trinity Place, San Antonio, TX, 78213
Abstract We report on the preparation, deposition, and activation of dendrimer stabilized nanoparticles as a new and versatile method for the preparation of supported metal catalysts. Using polyamidoamine (PAMAM) dendrimers as metal nanoparticle templates and stabilizers, Pt nanoparticles with very narrow size distributions can be prepared in aqueous solution. After deposition onto an appropriate support, the organic dendrimer must be removed to prepare active heterogeneous catalysts. Activation (removal of the dendrimer) under O2, H2, and He was examined using in-situ infrared spectroscopy and infrared spectroscopy of adsorbed CO. Activation of the supported precursors in solution was also investigated by refluxing the supported DENs in solvent/acid mixtures. The solvent, acid, and reflux time were all varied. The activated catalysts were characterized with Atomic Absorption Spectroscopy, Infrared Spectroscopy of adsorbed CO, CO chemisorption, CO oxidation catalysis, and toluene hydrogenation catalysis. Attempts to remove the dendrimer in solution generally resulted in loss of Pt, although choosing appropriate reflux conditions minimized the leaching. Oxidation under flowing O2/He followed by reduction under flowing H2/He was found to be the best means of activating the DENs.
