R. Taha et D. Duprez, NEW CHARACTERIZATION METHOD OF POSTCOMBUS TION CATALYSTS, Journal de chimie physique et de physico-chimie biologique, 92(7-8), 1995, pp. 1506-1520
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.