EFFECT OF THE PREPARATION PROCEDURE ON THE PROPERTIES OF 3-WAY AUTOMOTIVE PLATINUM-RHODIUM ALUMINA-CERIA CATALYSTS

The properties of three-way automotive Pt-Rh/Al2O3-CeO2 catalysts prep ared either by coimpregnation of the two noble metals (CI catalysts) o r by a newly devised technique of successive impregnations with an int ermediate reducing treatment (SI catalysts) were investigated for the oxidation of a propane-propene mixture under lean conditions and for t he CO + NO reaction, After high-temperature aging, bimetallic CI catal ysts are far less active than SI catalysts for propane oxidation. On t he other hand, they show comparable activities for propene oxidation a nd reaction CO + NO. The characterization of,bimetallic catalysts by T PR and FT-LR experiments suggests that the coimpregnation leads to an intimate interaction between platinum and rhodium while rhodium added by successive impregnations with a reduction step after platinum impre gnation would be selectively deposited onto cerium oxide surface in th e vicinity of platinum particles, avoiding the formation of Pt/Rh allo y.