Nanoscale Structure of Oxidized and Reduced Rhodium-Loaded ZrO2–CeO2 Catalysts

Transmission electron microscopy (TEM) was used to investigate microstructure and chemistry of Rh-loaded ZrO2–CeO2 catalyst exposed to oxidizing and two types of reducing atmospheres. In the oxidized sample Rh was dispersed on the ceria–zirconia support, while metallic Rh was precipitated in both H2 and CO reduced samples. The size distribution of Rh particles in the H2-reduced sample is narrower than in samples reduced in CO. Electron energy-loss spectroscopy (EELS) fine structure indicates that both Ce4+ and Ce3+ coexist in the oxidized sample while the reduced sample appears to be predominantly Ce3+. We discuss the orientation relations of Rh and the ceria–zirconia support and the formation of superstructure in ceria-zirconia support in the reduced samples. We also briefly discuss the thermodynamics of the Rh particle reduction and on ordering in the yttrium/lanthanum-doped ceria–zirconia.