In Situ Tracking of Pt Migration from Pt/Al₂O₃ to CeO₂ on the Atomic and Reactor Scale

Pt through the gas phase in the form of volatile PtO₂ has become a topic of interest within recent years due to its application in the production of single atom catalysts. It is furthermore important for oxidation reactions that take place at high temperatures, e. g. , CH₄ oxidation in order to track noble metal loss. Here, platinum migration is observed on the nanometer scale for mixed Pt/Al₂O₃ and CeO₂ nanoparticles as grinded powders. Furthermore, Pt migration within a reactor in a dual bed of Pt/Al₂O₃ followed by a bed of sieved CeO₂ particles is tracked in situ on the millimeter scale via time and spatially resolved X-ray absorption spectroscopy. It is observed that gaseous PtO₂ is first captured at the beginning of the CeO₂ bed. When the beginning of the bed appears saturated, PtO₂ adsorbs further downstream. Such adsorption behavior has to our knowledge not yet been reported in the literature since it requires time and spatially resolved in situ tracking. Furthermore, preferential adsorption sites of Pt on CeO₂ were identified using experimental extended X-ray absorption fine structure data and fitting based on models from Density Functional Theory calculations. They point to geometries as, for example, found in 4-fold hollow sites on CeO₂ (110) with additional ligands for stabilization.