Size control of Pt clusters on CeO2 nanoparticles via an incorporation-segregation mechanism and study of segregation kinetics
Recent literature on Pt/CeO2 catalysts reveals that ionic Pt species could be incorporated into the CeO2 lattice. Here we present a detailed study of Pt segregation in air and under a reducing atmosphere conducted on thermally treated samples by high-resolution X-ray diffraction (XRD) and X-ray absorption spectroscopy. We further perform a kinetic study by in situ XRD measurements with the aim of estimating the activation energy for Pt cluster segregation and coalescence in air, which was found to be similar to 3.88 eV. This high activation energy indicates that Pt clusters are strongly anchored on the CeO2 surface and that their mobility is activated only at >900 degrees C. We clearly show the correlation between the nature of the segregated Pt particles and the applied thermal treatment for Pt/CeO2 nanomaterials prepared by the wet chemical route. On the basis of thorough characterization, we present a possible segregation pathway under oxidizing conditions as opposed to a mere surface reduction during a reducing treatment, leading to the coalescence of less anchored Pt. The catalytic performances confirm the remarkable activity and thermal stability of entities obtained via an incorporation-segregation mechanism.