When sizes of supported metal particles are at the nanoscale, they exhibit specific catalytic properties often related to geometric and/or electronic effects. At this scale the influence of metal-support interactions is also magnified.  Therefore, the ability to control the dimensions of metal particles is particlularly important for the rational design of catalytic materials. Since conventional preparations do not provide the required degree of control over the structure and composition of supported metals, alternative synthetic routes have been proposed.  One of them is based on the use of poly(amidoamine) dendrimers as templating agents.  While some literature reports demonstrate that dendrimer-stabilized nanoparticles can be successfully deposited onto metal oxide supports and the resulting materials exhibit narrow particle size distributions, there are many challenges associated with this techique.  For example, little is known regarding the extent to which noble metals are complexed with the dendrimers in solution and what factors influence the complexation process.  Furthermore, high temperature thermal treatments used to remove the dendrimer component frequently lead to sintering of the supported metal particles. Our goal was to systematically address these challenges and develop a better molecular-level understanding of the processes taking place during the synthesis of (Pt, Rh)-PAMAM nanocomposites, used as precursors for the preparation of supported catalysts.  Results of AA, UV-Vis, FTIR, XPS, EXAFS, and STEM measurements illustrate how the metal/dendrimer ratio, the dialysis sequence, the solution pH, and the choice of the dendrimer removal procedure can influence the extent of metal-to-dendrimer binding and the dispersion of the resulting supported metal species.

Dendrimer mediated synthesis of supported Rh and Pt catalysts: Challenges and solutions

243rd National Meeting (2012)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.