Titania-Supported Au and Pd Composites Synthesized from Dendrimer-Encapsulated Metal Nanoparticle Precursors

Two different approaches are compared for preparing titania-supported Au and Pd using dendrimer-encapsulated nanoparticle (DENs) precursors. First, preformed dendrimer-encapsulated nanoparticles (1−2 nm in diameter) were deposited onto a commercial solid-oxide support via wetness impregnation. Second, the same DENs were incorporated into an amorphous titania network prepared using sol−gel chemistry. The latter approach is especially interesting, because in this case both the inside and the outside of the dendrimer act as templates:  the exterior of the dendrimer templates pores within the sol−gel matrix, and the interior templates the metal nanoparticles. In all cases, the dendrimer can be removed by calcination to leave behind the metal nanoparticles. The wetness impregnation method leads to a 4-fold increase in the average Au nanoparticle size following calcination. Significantly, less than a 2-fold increase in particle size was found for the sol−gel approach.