Transient Au–CO Complexes Promote the Activity of an Inverse Ceria/Gold Catalyst: An Insight from Ab Initio Molecular 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 out ab initio molecular dynamics (AIMD) simulations and standard density functional theory (static DFT) computations. To this end, we studied ceria clusters (Ce10O20/19) 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 O2 for 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 O2 molecule adsorbed at a perimeter site between ceria and Au reacts with a second CO molecule to CO2 and 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).