Characterization of the Local Structure of CeO2/ZrO2 by Pulsed Neutron Scattering

The use of cerium oxide as an oxygen storage component in automotive three-way catalysis has been well established. More recently the need to thermally stabilize these materials against deactivation at higher temperatures has focused attention on doping of the ceria with a wide range of metal oxides. The role of these dopants in the stabilization mechanisms for ceria is not completely understood as they must perform the complex role of sintering inhibitor while promoting oxygen storage and release. The scattering of pulsed neutrons produced by a spallation source coupled with the Fourier analysis provides a powerful method to characterize the local atomic structure of complex systems such as mixed oxides. We demonstrate that by using this method it is possible to obtain valuable information on the local atomic structure of the CeO₂/ZrO₂ catalyst support that cannot be attained by the conventional diffraction methods. In particular we found that the CeO₂/ZrO₂ catalyst support that shows a high oxygen storage capacity is phase segregated at a nanometer scale. We suggest that the CeO₂/ZrO₂ interfaces may destabilize oxygen, making the release of oxygen easier, and also provide easy diffusion of oxygen. The in-situ annealing study showed that strong grain growth occurs for nano-crystalline CeO₂ by annealing above 600°C, while significant changes in the local structure are observed even at lower temperatures.