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

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Abstract
An investigation of the structure of the bimetallic clusters present in rhodium–copper catalysts was conducted with the use of extended x‐ray absorption fine structure (EXAFS) measurements. Two catalysts were studied, both employing silica as a support for the clusters and both containing 1 wt. % rhodium. In one catalyst the Cu:Rh atomic ratio was 1:2 and in the other 1:1. Studies were made of the EXAFS associated with the Kabsorption edges of the rhodium and copper. The results of the EXAFS studies indicate that copper concentrates at the surface of the rhodium–copper clusters. In this regard the results are similar to our earlier reported results on ruthenium–copper clusters. However, the extent of surface segregation of the copper appears to be less pronounced for rhodium–copper clusters. This result is reasonable on the basis that rhodium and copper, unlike ruthenium and copper, exhibit at least some miscibility in the bulk.