Modelling of the metallic phases of different Pt-Rh/Al2O3-CeO2 catalysts: influence of the rhodium loading and nature of the metallic precursors

The activities for propane-propane mixture oxidation under lean conditions were found to be strongly different in the case of three-way Pt-Rh/Al2O3-Ce O2 catalysts prepared either by coimpregnation of the metallic salts (CI ca talysts) or by an original method of successive impregnations with an inter mediary reducing treatment (SI catalysts). Based upon the analysis of results of catalytic tests and physical characte risations including EXAFS at the Pt edge, it was shown previously that such a different behaviour for propane oxidation could easily be explained. The formation of clusters of inactive Pt-Rh alloys of a rather homogeneous com position was suggested for CI catalysts while active bimetallic catalysts o btained by the SI preparation procedure were modelled by Pt and Ph clusters more or less mixed together. To achieve the complete description of the metallic species (especially for SI catalysts), the influence of rhodium loading and the nature of the meta llic precursors were examined by studying the different catalysts by EXAFS mainly at the Pt edge but also at the Ph edge. (C) 2000 Elsevier Science B. V. All rights reserved.