Abstract
Abstract Three-way automotive Pt-Rh catalysts were prepared either by coimpregnation of the two noble metals (C.I. catalysts) or by an original method of successive impregnations with a reduction step after platinum impregnation (S.I. catalysts). It was shown that addition of rhodium can lead to opposite effects on the activity of platinum deposited on alumina-ceria for the reaction of propane oxidation, according to the preparation procedure: the coimpregnation of the two metals induces an inhibition of platinum activity when the addition of rhodium by successive impregnations leads to the reverse effect. The differences between the two preparations are greater on oxidized samples after aging at high temperature (900°C). These results are explained by the formation of alloy particles on coimpregnated catalysts while rhodium added by successive impregnations would be selectively deposited on surface cerium, avoiding the formation of Pt-Rh alloy. Energy dispersive spectroscopy fitted to a STEM unit allowed to bear out such hypothesis.
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