Catalysis by Supported Metal Clusters with Nearly Molecular Structures

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9315340 Gates The objectives of this effort are to prepare uniform supported metal clusters (close to molecular size), characterize their structures, and test them as catalysts. Iridium and platinum clusters of systematically varied sizes on metal-oxide (magnesia or alumina) supports are made from polynuclear organometallic precursors on the supports; the carbonyl-cluster precursors are treated under conditions that yield, as nearly as possible, decarbonylated metal clusters with the same numbers of metal atoms and the same metal framework structures as the precursors. The structures of the decarbonylated clusters, such as tetrairidium or hexairidium, are determined using extended X-ray absorption fine structure (EXAFS) spectroscopy, hydrogen chemisorption, electron microscopy, scanning tunnelling microscopy (STM), and atomic force microscopy (AFM). The samples are tested as catalysts for hydrogenation of cyclohexene, hydrogenation of benzene, hydrogenolysis of n-butane, and dehydrocyclization of n-hexane. Relationships between catalytic properties and cluster structures are attempted. Very small (less than a nanometer) particles (clusters) of metal on supports offer high reproducibility and very efficient use of expensive precious metals; they may also provide unique catalytic properties. This is a continuation of the seminal and pioneering effort in this area and offers the promise of improved performance and higher efficiency in a variety of chemical, petrochemical, and fuel refining operations. ***