NEW CHARACTERIZATION METHOD OF POSTCOMBUS TION CATALYSTS

Two series of PtRh/Al2O3 and PtRh/CeO2-Al2O3 catalysts were prepared f rom chlorine free precursors, Pt(NH3)(NO2)(2) and Rh(NO3)(3). They wer e then sintered (1% O-2/N-2 + 10% H2O) at 700 and 900 degrees C for tw o hours. These two series of catalysts were characterized by equilibra tion reactions O-16(2) + O-18(2) (at 300 degrees C for PtRh/Al2O3 and at 200 degrees C for PtRh/CeO2-Al2O3) and H-2 + D-2 (at 0 degrees C). The first reaction was faster over Ph and the second reaction over Pt. The two reactions may be used to determine the composition of the sur face of bimetallic catalysts. There was no surface enrichment of the f resh samples neither in Pt nor in Ph. After sintering at 700 degrees C and 900 degrees C, a significant enrichment of Ph was observed on the surface, when the atomic ration of Ph (%Rh/(Rh+Pt)) was higher than 4 0% Ph. On the contrary, when the atomic percentage of Ph is lower then 40% an enrichment in Pt can be observed.