CO oxidation and toluene hydrogenation by Pt/TiO₂ catalysts prepared from dendrimer encapsulated nanoparticle precursors

Generation 4 hydroxyl terminated polyamidoamine (PAMAM) dendrimer encapsulated nanoparticles (DENs) were examined as precursors for Pt/TiO ₂ catalysts. In this preparation method, the dendrimers were initially used to template and stabilize Pt nanoparticles in solution. DENs were then deposited onto titania, and activation conditions for dendrimer thermolysis were examined. The interactions between PAMAM dendrimers and the titania were found to differ from previous reports of dendrimersupport interactions with silica, alumina, and zirconia. In the case of titania, the amide bonds were found to shift 100 cm^-1, indicating adsorption occurs primarily through amide-titania interactions. Infrared spectroscopy, CO oxidation catalysis, and toluene hydrogenation catalysis were used to evaluate protocols for removing the dendrimer. Thermal decomposition of the DENs in O₂ or CO/O₂ atmospheres led to the formation of surface isocyanates that were preferentially bound to the metal nanoparticles. CO oxidation catalysis was insensitive to the activation protocol used, and infrared spectroscopy of adsorbed CO showed only small differences in the basic surface properties of the resulting Pt catalysts. Toluene hydrogenation catalysis was more sensitive to different activation pretreatments. The most active hydrogenation catalysts resulted from short, low temperature (150 °C) hydrogen treatments while longer treatments at higher temperature (300 °C) resulted in slightly less active catalysts.