Structure of bimetallic clusters. Extended x-ray absorption fine structure (EXAFS) of Pt--Re and Pd--Re clusters

Extended x-ray absorption fine structure (EXAFS) studies were conducted on catalysts containing platinum and rhenium, or palladium and rhenium, on alumina. The atomic ratio of rhenium to either platinum or palladium was close to one in the catalysts investigated. The metallic entities in the catalysts were characterized by analyses of the EXAFS associated with the L/sub I/ absorption edge of platinum, the L/sub III/ edge of rhenium, and the K absorption edge of palladium. It was concluded that Pt--Re and Pd--Re bimetallic clusters are present in the catalysts. However, the clusters have regions rich in rhenium and other regions which are rich in either platinum or palladium. Exposure of Pt--Re clusters to sulfur has little influence on their structure