Gw. Graham et al., Characterization of model automotive exhaust catalysts: Pd on Zr-rich ceria-zirconia supports, CATAL LETT, 67(2-4), 2000, pp. 99-105
Model Pd automotive three-way catalysts were prepared with high-surface-are
a Zr-rich ceria-zirconia powders as support materials, aged for 12 h at 105
0 degrees C under redox conditions simulating automotive exhaust gases, and
characterized by a combination of techniques including oxygen storage capa
city (OSC) measurements. Differences in OSC amongst aged catalysts made wit
h materials of similar ceria-zirconia compositions, but produced by differe
nt processes, were weakly correlated with differences in support surface ar
ea. Evidence of encapsulation of Pd particles was found in most of the aged
catalysts. The promotional effect of zirconia on ceria reducibility, well
known from previous temperature-programmed H-2 reduction studies, was appar
ent in Ce 3d core-level spectra from X-ray photoelectron spectroscopy measu
rements, which showed that both X-ray-induced and H-2 reduction become incr
easingly facile with increasing zirconia content. A slight Ce enrichment at
the surface of the fresh catalysts made with the more Zr-rich powders was
found to increase upon aging.