<i>In Situ</i> Tracking of Pt Migration from Pt/Al ₂ O ₃ to CeO ₂ 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.