In Situ Study of the Oxygen-Induced Transformation of Pyrochlore Ce₂Zr₂O_7+x to the κ-Ce₂Zr₂O₈ Phase

Temporary storage of oxygen in a solid catalyst is imperative for many important industrial oxidation reactions in the gas phase, for instance the post-treatment of automotive exhaust gas. A peculiar mixed Ce–Zr (1:1) oxide, the ordered κ-Ce 2 Zr 2 O 8 phase, is a promising catalytic material exhibiting an extraordinarily high oxygen storage capacity (OSC) and high thermal and chemical stability. We elucidate the temperature-dependent transformation between the pyrochlore pyr -Ce 2 Zr 2 O 7 and κ-Ce 2 Zr 2 O 8 phase upon oxygen uptake by in situ X-ray diffraction, X-ray absorption, and in situ Raman spectroscopy, providing insights into the electronic and structural changes on the atomic level, which are at the heart of the extraordinarily high OSC. We demonstrate that the Ce 3+ concentration can be followed during transformation in situ by Raman spectroscopy of the electronic spin flip in the f-shell of Ce 3+ . The catalytic activity of the κ-Ce 2 Zr 2 O 8 phase was investigated without an additional active component such as noble metals (Pt, etc.). While the high OSC of the κ-phase is beneficial for the oxidation of CO, the oxidation of HCl turns out to be unaffected by the high OSC.