(188c) Multi-Scale Investigation of Pd/Ceria Catalysts Via Density Functional Theory and Classical Reaxff Simulations

Oxide formation on palladium surfaces impacts the activity and selectivity of Pd/ceria catalysts toward hydrocarbon activation. Results derived from Density Functional Theory (DFT) suggest that mixed Pd_xCe_1-xO_δ surface oxides are stable under oxidizing reaction conditions, and that these oxides form unique Pd-O-Ce linkages that enable Pd to cycle between oxidization states enabling them to facilitate hydrocarbon activation. Although these mixed surface oxides are highly active, there is little consensus as to the exact nature of these sites. Indeed, many conflicting examples can be found indicating that either metallic Pd clusters or oxidized Pd surface species must be present on the catalyst surface to achieve high activity. Since DFT-based methods are limited to highly idealized surface models, they cannot easily assess Pd oxidation state transitions and geometry transformations at the complex cluster/support interface.  We have developed a classical Pd/Ce/O interaction potential for the ReaxFF reactive force field to examine the metal-support interface. With this interaction potential, we employ hybrid Monte Carlo/molecular dynamics methods to supported Pd clusters to assess the formation of mixed Pd-Ce interfacial oxides under varying reaction conditions. Initial results indicate that Pd-O-Ce structures similar to those identified in the mixed Pd_xCe_1-xO_δ surface oxide form at the Pd/ceria interface, suggesting that the interface is responsible for hydrocarbon activation in traditionally prepared catalysts featuring ceria-supported Pd clusters.