Microstructure of a Pd/ceria???zirconia catalyst after high-temperature aging

A model automotive exhaust catalyst, consisting of 2.25 wt% Pd supported on initially high-surface-area (88 m 2 /g) cerium???zirconium mixed oxide (Ce 0.5 Zr 0.5 O 2), was studied by X-ray diffraction (XRD), thermogravimetric analysis (TGA), and transmission electron microscopy (TEM), following high-temperature (1150??C) redox aging. Spherical Pd particles with size varying from 30 to 80 nm in diameter were found to be embedded both within single grains and at interfaces between multiple grains of the mixed oxide. X-ray energy-dispersive spectroscopy (EDS) and microbeam electron diffraction show that these particles are pure Pd, with face-centeredcubic structure. These results, together with elemental distribution maps obtained by EDS imaging, provide detailed visualization of an encapsulation phenomenon previously reported on the basis of XRD and TGA measurements alone.