The Role of Reducible Oxide–Metal Cluster Charge Transfer in Catalytic Processes: New Insights on the Catalytic Mechanism of CO Oxidation on Au/TiO₂ from ab Initio Molecular Dynamics

Abstract

To probe metal particle/reducible oxide interactions density functional theory based ab initio molecular dynamics studies were performed on a prototypical metal cluster (Au20) supported on reducible oxides (rutile TiO2(110)) to implicitly account for finite temperature effects and the role of excess surface charge in the metal oxide. It is found that the charge state of the Au particle is negative in a reducing chemical environment whereas in the presence of oxidizing species coadsorbed to the oxide surface the cluster obtained a net positive charge. In the context of the well-known CO oxidation reaction, charge transfer facilitates the plasticization of Au20, which allows for a strong adsorbate induced surface reconstruction upon addition of CO leading to the formation of mobile Au-CO species on the surface. The charging/discharging of the cluster during the catalytic cycle of CO oxidation enhances and controls the amount of O2 adsorbed at oxide/cluster interface and strongly influences the energetics of all redox steps in catalytic conversions. A detailed comparison of the current findings with previous studies is presented, and generalities about the role of surface-adsorbate charge transfer for metal cluster/reducible oxide interactions are discussed.

Face the Edges: Catalytic Active Sites of Nanomaterials

“…When the proper metal core is selected, optimization of homogeneous catalyst relies mainly on altering the ligands around metal to tune the electronic structure to achieve suitable binding or releasing. For “metal on support” catalyst, to tune the performance requires the optimization of metals and selection of supports, while the supports are not innocent during catalytic reactions in many cases 22, 23, 24. For NPs as catalysts, the optimizations of their performances are mainly achieved by tailoring their morphologies.…”

“…The SMSI effects are detrimental in many cases,88, 89 thus researchers would like to avoid them and choose inert supports in early studies. Recently, more and more examples16, 22, 23, 90, 91 proved that the supports might promote some reactions and enhance the total catalytic activities.…”

“…In other cases, there are many beneficial SMSI effects on metal oxides support metals,23, 111 and sometimes the enhanced performance cannot simply derive from “coordinate unsaturated”. When using reductive metal oxides as supports, the reducing nature of supports would whether donate or withdraw charges from metals near the metal/oxide interface, depending on the work functions of two materials 22. SMSI effects cannot be simply concluded.…”

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“…The crucial roles of CO molecule to facilitate catalytic methane conversion have been emphasized. The introduction of CO can lead to effective engineering of the geometric and electronic structures of the active metal centers, as reported in coordination chemistry, organometallic chemistry, and catalytic chemistry [13][14][15][16].…”