In Situ 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 PtO$_2$ 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., CH$_4$ oxidation in order to track noble metal loss. Here, platinum migration is observed on the nanometer scale for mixed Pt/Al$_2$O$_3$ and CeO$_2$ nanoparticles as grinded powders. Furthermore, Pt migration within a reactor in a dual bed of Pt/Al$_2$O$_3$ followed by a bed of sieved CeO$_2$ particles is tracked in situ on the millimeter scale via time and spatially resolved X-ray absorption spectroscopy. It is observed that gaseous PtO$_2$ is first captured at the beginning of the CeO$_2$ bed. When the beginning of the bed appears saturated, PtO$_2$ 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 CeO$_2$ were identified using experimental extended X-ray absorption fine structure data and fitting based on models from Density Functional Theory calculations. ... mehrThey point to geometries as, for example, found in 4-fold hollow sites on CeO$_2$ (110) with additional ligands for stabilization.