MICROSTRUCTURE OF A PD CERIA-ZIRCONIA CATALYST AFTER HIGH-TEMPERATUREAGING/

A model automotive exhaust catalyst, consisting of 2.25 wt% Pd support ed on initially high-surface-area (88 m(2)/g) cerium-zirconium mixed o xide (Ce0.5Zr0.5O2); was Studied by X-ray diffraction (XRD), thermogra vimetric analysis (TGA), and transmission electron microscopy (TEM), f ollowing high-temperature (1150 degrees C) redox aging. Spherical Pd p articles with size varying from 30 to 80 nm in diameter were found to be embedded both within single grains and at interfaces between multip le grains of the mixed oxide. X-ray energy-dispersive spectroscopy (ED S) and microbeam electron diffraction show that these particles are pu re Pd, with face-centered-cubic structure. These results, together wit h elemental distribution maps obtained by EDS imaging, provide detaile d visualization of an encapsulation phenomenon previously reported on the basis of XRD and TGA measurements alone.