Structurally simple, highly dispersed, supported metal catalysts are prepared and characterized. The catalysts are prepared from organometallic precursors which are converted into organometallic clusters of defined structures on the surfaces of basic supports (magnesia and lanthana); subsequent decarbonylation gives clusters of supported metal atoms with the same number of atoms as the precursors. The metals used in this study are iridium and platinum. Samples are characterized with infrared spectroscopy, extended X-ray adsorption fine structure (EXAFS), and transmission electron microscopy; catalytic activities and selectives are measured for hydrocarbon conversion reactions. This is a fundamental study of the effects of dispersion near the upper limit (or, equivalently, the effects of cluster size in small clusters) on the catalytic properties of metals. The issue is a critical one for the optimization of systems employing rare-metal catalysts for a variety of industry energy and environmental purposes.
