Transient Au-CO Complexes Promote the Activity of an Inverse Ceria/Gold Catalyst: An Insight fromAb InitioMolecular Dynamics

To probe particle-support interactions and their mechanistic role for catalytic CO oxidation on nanoporous gold (np-Au) coated with ceria nanoparticles, we carried outab initiomolecular dynamics (AIMD) simulations and standard density functional theory (static DFT) computations. To this end, we studied ceria clusters (Ce₁₀O_20/19) supported on a Au(321) surface exhibiting a high density of steps and kinks. Our theoretical model represents the structurally inverse situation compared to more commonly studied ceria-supported Au nanoparticle systems. In agreement with previous results for Au(111), we find that reduced (Ce₁₀O₁₉) as well as stoichiometric (Ce₁₀O₂₀) ceria nanoparticles transfer electrons to the Au(321) support. This charge transfer (particularly strong in the case of Ce₁₀O₁₉) reflecting a strong chemical interaction between ceria and Au is probably responsible for the stabilization of np-Au against thermal coarsening experimentally observed upon deposition of oxide nanoparticles. The adsorption energies of the ceria cluster on Au(321) are more negative than on the Au(111) surface by around ∼0.5 eV. AIMD simulations were employed to study the mechanism of catalytic CO oxidation with O₂for the ceria/Au(321) system. We found that a CO molecule adsorbed near the ceria/gold perimeter interface can extract a Au atom from the surface in the form of a mobile linear Au-CO complex, which results in a very low activation energy when this species reacts with lattice O to CO₂. The released bare Au adatom subsequently attaches to a step edge of the gold surface, leading to a dynamic restructuring of the Au support. Next, an activated O₂molecule adsorbed at a perimeter site between ceria and Au reacts with a second CO molecule to CO₂and an adsorbed O atom, which eventually fills the vacancy site created in the first half of the cycle. As compared to ceria particles supported on Au(111), the reactivity is enhanced as a new low-energy mechanism is enabled, revealing the positive impact of the stepped structure of Au(321).