Decomposition and activation of Pt-dendrimer nanocomposites on a silica support

Zero valent platinum nanoparticles were stabilized in solution by the use of poly( amido) amine dendrimers and were subsequently deposited onto a porous silica support. The resulting materials were subjected to various thermal treatments in oxidizing, reducing, and inert environments, in order to remove the surrounding polymer and expose the Pt metal sites to gas phase reagents. The materials were characterized at several different stages during this process via Fourier-Transform Infrared ( FTIR) spectroscopy and Transmission Electron Microscopy (TEM). The results suggest that the dendrimer decomposition occurs at its mono-substituted amide groups and begins at relatively low temperatures (similar to50 degreesC). The presence of oxygen in the gas phase and the Pt particles in the Pt-dendrimer nanocomposite accelerate this process. Oxidation at 425 degreesC was the most successful temperature for removing the dendrimer fragments from the Pt surface, rendering the Pt sites most accessible for carbon monoxide adsorption. Limited sintering of the Pt particles is observed under these conditions, as well as during subsequent reduction steps, necessary to yield the metallic form of Pt.