2, Frederic Seitz Material Research Laboratory, Urbana, Illinois, United States
The supported metal nanocatalysts often show different catalytic activity depending on the supporting oxide materials. This implies that support-metal interaction can redirect the chemical reaction on the metal catalyst and that an additional phase (overlayer) can form on the surface or at the interface of the metal catalyst. Although little is known about the structure and the properties of the overlayers, promising results have been reported that some phases can selectively activate the adsorption of certain types of molecules. Here, we investigate the structure and the stability of the overlayer on the supported metal nanocatalyst during oxidation using environmental transmission electron microscope.
The results show that the overlayers form and encapsulate the Pd metal nanocatalysts supported on the reducible oxide, e.g. titania, of which cations migrated to the metal surface. The structure of the overlayer resembles the surface structure of the support oxide, but with the unique lattice parameters. The stability of the overlayer was studied by varying the temperature and the pressure and the results are addressed by the thermodynamic terms. The surface and the interfacial stress are also considered to explain the unique structures on the metal nanocatalyst.