INFLUENCE OF THE REDOX PROPERTIES OF CERIA ON THE PREPARATION OF 3-WAY AUTOMOTIVE PLATINUM-RHODIUM ALUMINA-CERIA CATALYSTS

The redox properties of ceria were investigated by temperature-program med reduction performed under hydrogen and the catalysts were evaluate d by determining the temperatures at which 50% conversion for propene and propane oxidation were reached, The results obtained show that cer ia plays a decisive role within the preparation of bimetallic Pt-Rh/Al 2O3-CeO2 catalysts by successive impregnations (SI) when reduced cappi ng cerium atoms (Ce3+) are present on the parent Pt/Al2O3CeO2 catalyst before introduction of the rhodium salt. Thus, rhodium deposition wou ld occur by a redox reaction between Ce3+ and Rh3+. The preparation pr ocedure of Pt-Rh/Al2O3-CeO2 catalysts by the SI method increases the t hermal stability of the metallic species under oxidizing conditions. T his improvement would be the consequence of a higher resistance to the formation of Pt-Rh alloys with surface enrichment in rhodium.