Catalysis by Supported Metal Clusters with Nearly Molecular Structures

小行星9315340 这项工作的目标是制备均匀的负载金属簇（接近分子大小），表征其结构，并测试它们作为催化剂。 在金属氧化物（氧化镁或氧化铝）载体上的系统地不同尺寸的铱和铂簇由载体上的多核有机金属前体制成;羰基簇前体在尽可能接近产生脱羰基金属簇的条件下处理，所述脱羰基金属簇具有与前体相同的金属原子数和相同的金属骨架结构。 的脱羰基簇，如四铱或hexairidium的结构，确定使用扩展X射线吸收精细结构（EXAFS）光谱，氢化学吸附，电子显微镜，扫描隧道显微镜（STM），和原子力显微镜（AFM）。 对样品进行了环己烯加氢、苯加氢、正丁烷氢解、 正己烷。 催化性能和集群结构之间的关系进行了尝试。 在载体上的非常小（小于纳米）的金属颗粒（簇）提供了高再现性和非常有效地使用昂贵的贵金属;它们还可以提供独特的催化性能。 这是该领域开创性工作的延续，并为各种化学、石化和燃料精炼操作提供了改进性能和更高效率的承诺。 ***

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. ***