Transition metal nanoparticles supported on ceria (e.g., Pt/CeOx and Pd/CeOx) have attracted widespread attention due to their excellent catalytic performance in combustion processes. Pd and Pt, for example, are common ingredients of three-way catalyst (TWC) convertor technology, mainly because of their good low-temperature (T &lt; 150°C) CO oxidation performance. An important property of ceria is its ability to release oxygen atoms from its lattice, allowing TWCs to retain good oxidation performance under fuel-rich operating conditions. Consequently, many studies of low-temperature CO oxidation over Pd/CeO2 focus on the oxidation state of Pd, the role of ceria O vacancies, and the specific topological features of the Pd-CeO2 interface. There is an ongoing debate regarding whether the active phase in Pd/CeO2 is oxidic or metallic. We use a genetic algorithm (GA) to identify the structure of a Pd8 cluster on the most stable surface termination of ceria, CeO2(111). The basin-hopping-based approach in the Gibbs ensemble at the DFT level (GCMC-DFT)) was used to optimize the structure of the Pd8/CeO2(111) system in equilibrium with gaseous O2 at a given chemical potential. These simulations confirm the oxidation of Pd during CO oxidation. For the optimized Pd8/CeO2 and Pd8Ox/CeO2(111) structures, we compute the kinetic barriers for all relevant steps involved in CO oxidation at the Pd-CeO2 interface. Microkinetics simulations show that the fully oxidized Pd8 catalyst presents the highest activity in CO oxidation. By using similar methods, we found that Pt8O14/CeO2 catalysts are more active than the single Pt atom decorated CeO2 catalyst, which supports our experimental measurements. This research presents an advanced modeling approach for determining the active catalyst structure and composition under reaction conditions, which we expect to become a standard technique given the rapid advances in computational power.

Identifying the active structures of metal nanoparticles supported on CeO2 for CO oxidation

2019 Spring National Meeting

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