Relationship between the zirconia-promoted reduction in the Rh-loaded Ce0.5Zr0.5O2 mixed oxide and the Zr-O local structure

Rh/CeO2-ZrO2 mixed oxides show improved redox properties compared to Rh/CeO2 due to a low-temperature reduction in the bulk. In the present work we have investigated the Zr-O and Ce-O local structure in Rh/Ce0.5Zr0.5O2 by means of EXAFS and Raman spectroscopy. By introducing Zr4+ into the CeO2 lattice, the oxygen sublattice is strongly modified compared to the ideal fluorite structure of CeO2: the Ce4+ ions retain their coordination while the number of oxygens around the Zr4+ decreases from 8 to 6 due to a displacement of two oxygens to a nonbonding distance. It is suggested that this distortion of the oxygen sublattice generates some mobile oxygens in Rh/Ce0.5Zr0.5O2 which are responsible for the improved redox properties.