EXAFS: Applications to supported bimetallic catalysts.

Abstract

Recent studies on the surface structure of several supported bimetallic catalysts by use of EXAFS spectroscopy are reviewed. EXAFS spectroscopy is a very powerful technique for investigating the structure of the supported bimetallic catalysts because it provides direct information on the metal-metal interactions. It is revealed that there exist various kinds of metal-metal interactions in the bimetallic systems. In RuCu/SiO2, copper atoms are dominantly located at the surface of the bimetallic particle, while, in PdAu/SiO2, the surface composition of the bimetallic particle is equal to the bulk. (That is, the alloy particles are formed.) Other types of metal-metal interactions are also discussed. Our recent EXAFS studies clearly revealed that the direct Rh0-Fe3+ bondings are present in the RhFe/SiO2 catalyst, and that in the RhCo/γ-Al2O3 system the cationic cobalt atoms are again directly bonded with the cationic rhodium atoms. In these systems, it is very important to characterize not only metal-metal but metal-support interactions in order to understand the relation between the surface structure and the catalytic properties.