Supported Bimetallic Cluster Catalysts

Abstract

We review synthesis, structural characterization, and catalysis by supported bimetallic clusters. Initial steps in the preparations include (a) adsorption of molecular metal clusters with preformed metal−metal bonds; (b) synthesis in zeolite cages; and (c) adsorption of a metal complex on a supported complex or cluster of another metal. Chemisorption capacities of supported oxophilic metal−noble metal clusters for hydrogen and CO are typically less than those of supported clusters of just the noble metal. Catalytic properties distinguishing supported bimetallic clusters from monometallics include high selectivities for oxygenates in CO hydrogenation and different selectivities for C═O vs C═C bond hydrogenation. Advantages of precise synthesis with organometallic precursors (smallness and uniformity of the supported clusters with bonds between the two metals) are offset by the expensive preparations and difficulty of catalyst regeneration. Applications of supported bimetallic clusters are most likely in specialty chemicals production or with stable combinations of oxophilic and noble metals.