Structure of bimetallic clusters. Extended x-ray absorption fine structure (EXAFS) studies of Ru–Cu clusters

Abstract

A study was made of the extended x-ray absorption fine structure (EXAFS) associated with the K absorption edges of ruthenium and copper in a silica supported ruthenium–copper catalyst containing 1.0 wt.% ruthenium and 0.63 wt.% copper (1:1 atomic ratio of ruthenium to copper). Previous chemisorption and catalysis studies indicated a strong interaction between the ruthenium and copper in the catalyst, and led to the suggestion that the catalyst consisted of bimetallic clusters of ruthenium and copper dispersed on the silica. The EXAFS data of this investigation provide information on the structure of the ruthenium–copper clusters. The ruthenium in the bimetallic clusters appears to be very similar to the ruthenium in a silica supported ruthenium reference catalyst, in that the ruthenium atoms are coordinated predominantly to other ruthenium atoms and only to a minor extent to copper atoms. By contrast, the copper atoms in the clusters have nearest neighbors which are more nearly equally distributed among copper and ruthenium atoms. The results are consistent with a model of a ruthenium–copper cluster in which the copper is present at the surface.