Electron microscopy studies of metal clusters: Ru, Os, RuCu, and OsCu

Abstract

Data on size and shape of bimetallic ruthenium-copper and osmium-copper clusters and of monometallic ruthenium and osmium clusters, all dispersed on a silica carrier, have been obtained by high-resolution electron microscopy. Cluster size distributions were determined from the electron micrographs. The clusters were also characterized by chemisorption data. The osmium and osmium-copper clusters exhibited extremely high dispersion, with average cluster diameters of 12 and 10 Å, respectively. The average diameters of the ruthenium and ruthenium-copper clusters were approximately threefold larger. In the case of ruthenium and ruthenium-copper, evidence of very thin clusters with raft-like shapes was obtained for clusters with diameters as large as 60 Å. It is concluded that the raft-like clusters of ruthenium consist of a single layer of atoms. In a raft-like ruthenium-copper cluster, a layer of ruthenium atoms covered by copper atoms is visualized. In certain catalysts, some of the larger clusters appear to be three dimensional rather than raft-like in form.