Characterization of model automotive exhaust catalysts: Pd on Zr-rich ceria-zirconia supports

Model Pd automotive three-way catalysts were prepared with high-surface-area Zr-rich ceria-zirconia powders as support materials, aged for 12 h at 1050 degrees C under redox conditions simulating automotive exhaust gases, and characterized by a combination of techniques including oxygen storage capacity (OSC) measurements. Differences in OSC amongst aged catalysts made with materials of similar ceria-zirconia compositions, but produced by different processes, were weakly correlated with differences in support surface area. 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 apparent in Ce 3d core-level spectra from X-ray photoelectron spectroscopy measurements, which showed that both X-ray-induced and H-2 reduction become increasingly 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.