Effect of the preparation procedure on the properties of three-way automotive platinum—rhodium/ alumina—ceria catalysts

The properties of three-way automotive PtRh/Al2O3CeO2 catalysts prepared either by coimpregnation of the two noble metals (CI catalysts) or by a newly devised technique of successive impregnations with an intermediate reducing treatment (SI catalysts) were investigated for the oxidation of a propane—propene mixture under lean conditions and for the CO + NO reaction. After high-temperature aging, bimetallic CI catalysts are far less active than SI catalysts for propane oxidation. On the other hand, they show comparable activities for propene oxidation and reaction CO + NO. The characterization of bimetallic catalysts by TPR and FT-IR 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 impregnation would be selectively deposited onto cerium oxide surface in the vicinity of platinum particles, avoiding the formation of Pt/Rh alloy.