Surface Chemistry of Mass-selected Precious Metal Clusters on Metal Oxide Surface

Abstract

The research focused on chemical properties on surface deposited mass-selected Pt_n clusters from the viewpoint of size-specificities and cluster-support interaction, is expected the key technology for reduction of precious metal usage of heterogeneous catalysts such as automotive exhaust catalysts. Mass-selected Pt_n clusters are deposited on a TiO₂(110) surface, catalytic activity measurements with a high pressure reaction cell show CO oxidation activities of mass-selected Pt_n clusters have a cluster size discontinuous dependency. We also obtained atomic-resolutional scanning tunneling microscope (STM) images of mass-selected clusters on surfaces, enabling the identification of atomic alignments in the clusters on the surface. Clusters smaller than Pt₇ lay flat on the surface with a planar structure and a planar-to-3D transition occurred at n=8 for Pt_n clusters on TiO₂. The geometric structures depend strongly on the number of atoms in the deposited cluster possibly because of the differences in binding energies and interaction with the surface. We find Pt clusters deposited on a TiO₂(110) surface make no aggregation, fragmentation nor coalescence at 650K using STM and X-ray photoelectron spectroscopy (XPS).