INVESTIGATION OF THE RH/TIO2 SYSTEM BY XPS AND XAES

The Rh-TiO2 interaction has been studied in connection with the strong metal-support interaction (SMSI) effect. Several deposits of rhodium on TiO2 in the concentration range 2 x 10(15)-2 x 10(16) atoms cm-2 were investigated. The changes in the spectra after heating in vacuum at approximately 550-degrees-C and after oxidation at 350-degrees-C followed by reduction in H-2 at 200-degrees-C have been studied. Negative shifts were observed in the Rh3d5/2 binding energies relative to the Ti2p3/2 line after heating. These shifts were explained predominantly by the shift of the Ti2p3/2 line as a result of a shift of the Fermi level towards the bottom of the conduction band caused by reduction of TiO2 during heating above 550-degrees-C. After heating at approximately 550-degrees-C, lower values of the Rh3d5/2 binding and RhM5VV kinetic energies (Fermi level referencing) as well as smaller widths of these lines were found. Two basic effects which would accompany the transition between the two states which were engendered by the two types of the treatments were considered: morphological and electronic changes. The observed phenomena were probably a consequence of the electronic influence of the reduced supported oxide on the rhodium clusters.