EXAFS INVESTIGATIONS OF LANTHANA-PROMOTED RH/SIO2 CATALYSTS

EXAFS investigations at the Rh K edge of lanthana-promoted Rh/SiO2 catalysts showed that the local environment of the Rh ions in the oxidic catalyst precursor state did not depend on the La2O3 content and resembled that of Rh2O3. No LaRhO3 formation could be detected. In the reduced state, EXAFS as well as H-2 and CO chemisorption demonstrated that La2O3 increased the Rh dispersion. Covering of the Rh metal particles by La2O3 was minor, because during catalyst preparation, La was impregnated prior to Rh.