Redox behaviour of a ceria–zirconia inverse model catalyst

•ZrO2-x(111) and CeO2-x(111) form a phase-separated structure when prepared at 1200 K. •ZrO2-x(111) undergoes photo-induced reduction when exposed to soft x-rays. •Reduction of ZrO2-x(111) is prevented by the addition of CeO2-x(111) indicating a synergy. The redox behaviour modification following the addition of zirconia to ceria nanostructures supported on Rh(111) has been investigated using a combination of Low Energy Electron Diffraction (LEED) and X-ray Photoemission Electron Microscopy (XPEEM). Soft X-ray irradiation was employed to reduce ZrO2-x(111) supported on Rh(111) and, by introducing oxygen, the reoxidation process of the thin film was monitored. Ceria was then depositied with zirconia. Using XPEEM, we determined that the mixed metal oxide formed a phase-separated structure with CeO2(111) nanoparticles on top of the zirconia. Upon exposure of CeO2-x/ZrO2-x/Rh(111) to X-ray illumination, the zirconia no longer undergoes any observable reduction while at the same time the ceria is reduced. Our results indicate a synergy between the zirconia and ceria in the phase-separated system expected in the working catalyst, with oxygen transfer between the metal oxides. This sheds light on the mechanism of the enhancement of catalytic properties seen with the addition of zirconia to ceria and highlights the oxygen storage and release ability of ceria. [Display omitted]