Extended x-ray absorption fine structure (EXAFS) of dispersed metal catalysts

Abstract

Extended x-ray absorption fine structure (EXAFS) studies were made in a series of highly dispersed metal catalysts to obtain structural information on the metal clusters present. Clusters of osmium, iridium, and platinum dispersed on silica or alumina were investigated. The metal clusters in the catalysts constituted 1.0 wt.% of the total mass. Chemisorption measurements indicated that the metal dispersions approached unity, where dispersion is defined as the ratio of surface metal atoms to total metal atoms in the clusters. When EXAFS data on the metal clusters are compared with data on the corresponding bulk metals, the lower average coordination number of the metal atoms in a cluster is evident. The decrease in coordination number is accompanied by an increase in the root mean square deviation of interatomic distance about the equilibrium value.