Synthesis and Characterization of Supported Metal Cluster Catalysts with Well-Defined Structures

Abstract

ABSTRACTNearly uniform supported metal clusters are the focus of this summary, which addresses their synthesis, characterization, and catalytic properties. Supported clusters represented as Ir4and Ir6were prepared on MgO powder by thermal decarbonylation of [HIr4(CO)11]−and [Ir6(CO)15]2−, respectively. The most useful characterization technique for supported clusters is extended X-ray absorption fine structure spectroscopy, but the structure data are limited by the precision of the coordination numbers (about ±20%). Ir4and Ir6clusters on supports catalyze hydrogenation of cyclohexene and of toluene, and they are catalytically distinct from larger iridium particles, although the reactions are structure insensitive (proceeding at about the same rate per exposed metal atom) when catalyzed by metal particles larger than about 1 nm. Thus the concept of structure insensitivity does not extend to supported metal clusters, which are regarded as quasi molecular.