CO Oxidation on the Au₁₅Cu₁₅ Cluster and the Role of Vacancies in the MgO(100) Support

Abstract

A comprehensive theoretical study of a Au 15 Cu 15 cluster on MgO(100) supports and its catalytic activity for CO oxidation has been performed based on the density functional theory and microkinetic modeling. Molecular adsorption and different reaction paths based on the Langmuir−Hinshelwood (LH) and Eley−Rideal (ER) mechanisms have been explored by tuning the location of vacancies in MgO(100). The charge states of the Au 15 Cu 15 cluster are negative on all supports, defect-free, O-vacancy (F-center), and Mg-vacancy (V-center), and the effect is significantly amplified on the F-center. In each case, the O 2 molecule can be effectively activated upon adsorption and dissociated to 2 × O atoms easily, and the reaction modeling takes into account also the reaction paths with adsorbed O atoms. Overall, CO oxidation has lower reaction barriers on the cluster on the F-center. The microkinetic modeling analysis reveals that CO oxidation is very sensitive to the CO partial pressure, as the relatively strong CO binding leads readily to CO poisoning of the cluster surface sites and hinders CO 2 formation. For low CO partial pressures, the catalytic reaction takes place already at 150 K for the cluster on the F-center. The CO 2 production rates are much lower for the defect-free and V-center supports which display similar increased activity at elevated temperatures. In all cases, the right combination of CO and O 2 partial pressures is instrumental for CO 2 production.

Computational Design of Clusters for Catalysis

“…For Au 15 Cu 15 supported on MgO, F-centers again facilitate CO oxidation, whereas Mg vacancies (V-centers) reduce the charge transfer to the cluster and harm the activity. However, the V-centers provide the strongest binding to the surface, making sintering less likely (93).…”

Elucidating the stability of ligand-protected Au nanoclusters under electrochemical reduction of CO2

“…The inherent stability exhibited by ligand protected NCs, along with their high surface-to-volume ratio, their precisely known surface structure, and discrete electronic states have made these NCs attractive functional materials for applications in catalysis [12][13][14][15][16][17][18][19][20][21][22][23][24][25], with the Au 25 NC being the most investigated NC for this purpose. Experimental and computational studies have demonstrated that the Au 25 NC exhibits exceptional catalytic behavior for the oxidation of styrene, CO, the hydrogenation of ketones and aldehydes, photocatalytic water splitting, and more recently, the electrochemical reduction of CO 2 [14,16,18,[20][21][22][25][26][27][28][29][30][31] .…”

Physico-Chemical Insights into Gas-Phase and Oxide-Supported Sub-Nanometre AuCu Clusters

“…Mozer et al [49] reported that high copper content in AuCu clusters can block the Au active sites, thus Cu-deficient clusters have increased catalytic activity for CO oxidation. Research of Ma and co-workers [8,50] on AuCu clusters on MgO showed that Au15Cu15 on MgO(100) has high activity for the dissociation of O2.…”

“…Studying sub-nanometre AuCu clusters, where quantum effects are observed and where "every atom counts" [51,52], is required in order to rationalize their catalytic activity and to form a base for future experimental investigations. To the best of our knowledge, detailed, systematic studies of MgO-supported sub-nanometre AuCu clusters have not been reported, despite many publications on the structural and catalytic properties of larger free and MgO-supported AuCu nanoparticles [8,50,[53][54][55]. Theoretically, sub-nanometre sizes present a synergistic combination between employing high level theory (e.g.…”