Transient Au–CO Complexes Promote the Activity of an Inverse Ceria/Gold Catalyst: An Insight from Ab Initio Molecular Dynamics

Abstract

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 (Ce 10 O 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 (Ce 10 O 19 ) as well as stoichiometric (Ce 10 O 20 ) ceria nanoparticles transfer electrons to the Au(321) support. This charge transfer (particularly strong in the case of Ce 10 O 19 ) 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 O 2 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 CO 2 . 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 O 2 molecule adsorbed at a perimeter site between ceria and Au reacts with a second CO molecule to CO 2 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).

Coadsorption Interfered CO Oxidation over Atomically Dispersed Au on h-BN

“…In reaction conditions, the thermodynamics-driven adsorption and reaction of substrates would change the oxidation state [ 5 ] and coordination of metal species drastically [ 6 ], and may stabilize metal species in an atomically dispersed form or promote their aggregation or redispersion [ 7 ]. This feature of transition metal species in reaction conditions were reported for Au [ 8 , 9 , 10 , 11 , 12 ], Pd [ 13 ], and Rh [ 14 ] -based SACs, etc. Apart from the potential aggregration/redispersion of metal species, the adsorption/coadsorption of the substrate may also impact the thermodynamics and kinetics for the evolution of reaction species and may lead to a switch of the pathways for substrate conversion with reactions conditions, such as temperature, substrate concentrations (partial pressures), [ 15 , 16 , 17 , 18 , 19 ] etc.…”

Unveiling the corrosion mechanism of 3-nitro-1,2,4-triazol-5-one (NTO) toward mild steel from ab initio molecular dynamics: how the “nitro-to-amino” reaction matters

“…Nevertheless, no further reactions were observed aer the amination of NTO and its anion on Fe(110), which can be attributed to the relatively short time scales of AIMD simulations which allow observation of only barrierless/low-barrier events lower than 0.5 eV. 56,70 In view of the dissociation constant of NTO in solution and the similarity of the ammoniation process, the possible decomposition mechanism of ATO was further studied with NTO as the initial reactant, which is also consistent with literature reports. 26,29,33 The possible reactions of ATO on Fe(110) and their corresponding barriers were calculated using the "slow growth" approach based on the experimental results.…”