Controlled oxygen chemisorption on an alumina supported rhodium catalyst. The formation of a new metal-metal oxide interface determined with EXAFS

An alumina-supported rhodium catalyst has been studied with EXAFS. After reduction and evacuation, oxygen was admitted at 100 and 300 K. EXAFS spectra of the catalyst after oxygen admission at 100 K indicated the beginning of oxidation. At 300 K only a small part of the rhodium particles remained metallic and this metallic 'kernel' was partly covered with rhodium oxide. In the rhodium metal to rhodium oxide interface the same 2.7-A Rho-0' distances are present as in the metal-support interface. A model is presented that explains the observed formation of the rhodium metal-rhodium oxide interface.