Synthesis of supported nanoparticles for catalytic applications

The performance of supported metal catalysts largely depends on the structure and composition of the metal particles and the nature of the support. In order to achieve better control over these parameters, synthetic routes based on the use of organometallic clusters and templating agents have been proposed. Among the different templating agents, poly(amidoamine) (PAMAM) dendrimers have attracted growing attention. In this thesis, in-situ EXAFS characterization was used to monitor the structural changes occurring during the various steps of the synthesis of dendrimer-derived supported Pt and Rh catalysts. The results indicate that there is no formation of zerovalent metal nanoparticles in solution. Such nanoparticles can be formed on the support upon deposition and drying of the metal-dendrimer nanocomposites. Pt nanoparticles thus obtained show relatively high mobility and tend to agglomerate during the thermal treatment required to remove the dendrimer shell. However, in the case of the Rh/ZrO2 catalyst the nanoparticles formed remain in the sub-nanometer size range even after thermal treatment demonstrating the advantage of this synthetic technique to obtain highly dispersed supported metal catalysts. PAMAM dendrimers were also employed successfully to prepare Ru catalysts with controlled particle sizes.;Organometallic cluster precursors were used to prepare structurally simple and uniform PtFe/SiO2 catalysts which can be used as models when compared to dendrimer-derived ones. The results obtained in this case indicate that the structure of the surface species depends on the treatment conditions used to remove the ligands and affects the catalytic performance during the oxidation of CO. More specifically, the CO oxidation activity was found to correlate with the presence of bimetallic Pt-Fe interactions and the strength of CO adsorption.;Finally, the formation of Pt colloids without the use of any surfactant or templating agent was investigated. A stable colloidal suspension of nearly uniform Pt4 clusters can be prepared by treatment of an aqueous solution of H2PtCl6 with NaBH4. These Pt 4 clusters were found to be active for the liquid phase oxidation of 2-propanol to acetone and can be also used as precursors for the preparation of highly dispersed Pt/gamma-Al2O3 catalysts.