CATALYTIC ACTIVITY AND EXAFS CHARACTERIZATION OF 3 WAY AUTOMOTIVE PT-RH AL2O3-CEO2 CATALYSTS FROM DIFFERENT PREPARATIONS/

Three way automotive Pt-Rh catalysts were prepared either by coimpregn ation of two noble metals (CI catalysts) or by an original method of s uccessive impregnations of Pt and Rh, a reduction step following the p latinum impregnation (SI catalysts). According to the preparation proc edure it was shown that, especially after oxidative treatment, rhodium can bring about opposite effects on the activity for propane oxidatio n of platinum atoms deposited on alumina-ceria. The coimpregnation pre paration induces an inhibition of platinum activity by the formation o f alloy particles with rhodium surface enrichment. On the other hand, SI procedure leads to a selective deposition of rhodium on reduced ato ms of cerium avoiding the formation of Pt-Rh alloy. By this way the pl atinum Pt-0 particles remain active for propane oxidation and are stab ilised at high temperature. Such simple description of these two kinds of catalysts, based on catalytic results and some previous physical a nalysis, must be adjusted by taking into account results of EXAFS char acterisation. With this complementary data it is then possible to give a better view of the bimetallic entities in the catalysts, especially concerning the distribution of the two metals in such entities. (C) 1 998 Elsevier Science B.V. All rights reserved.