A comparative theoretical study of the catalytic activities of Au 2 - and AuAg- dimers for CO oxidation

Abstract

The detailed mechanisms of catalytic CO oxidation over Au(2)(-) and AuAg(-) dimers, which represent the simplest models for monometal Au and bimetallic Au-Ag nanoparticles, have been studied by performing density functional theory calculations. It is found that both Au(2)(-) and AuAg(-) dimers catalyze the reaction according to the similar mono-center Eley-Rideal mechanism. The catalytic reaction is of the multi-channel and multi-step characteristic, which can proceed along four possible pathways via two or three elementary steps. In AuAg(-), the Au site is more active than the Ag site, and the calculated energy barrier values for the rate-determining step of the Au-site catalytic reaction are remarkably smaller than those for both the Ag-site catalytic reaction and the Au(2)(-) catalytic reaction. The better catalytic activity of bimetallic AuAg(-) dimer is attributed to the synergistic effect between Au and Ag atom. The present results provide valuable information for understanding the higher catalytic activity of Au-Ag nanoparticles and nanoalloys for low-temperature CO oxidation than either pure metallic catalyst.

Catalytic activity of anionic Au–Ag dimer for nitric oxide oxidation: a DFT study

“…This indicates that O 2 prefers to bind to Ag-site of AuAg À similar to the previous study. 17 This fact was further confirmed by calculated longer O-O distance (1.390 Å) in AuAg À -O 2 than that in AgAu À -O 2 (1.373 Å), which were in close agreement with previously reported values. 17 The amount of electron transfer from the dimer to O 2 in these two complexes was 0.645 e in AuAg À -O 2 and 0.557 e in AgAu À -O 2 .…”

“…Previous investigations 17,[29][30][31][32][33] showed that the B3LYP functional was sufficiently accurate for describing noble-metal systems. To further verify the reliability of our methods, we also calculated the bond lengths for Au-Ag À , NO and O 2 and dissociation energy calculations for Au-Ag À and NO to compare the corresponding experimental values.…”

“…Considering the catalytic activity of Au 2 À dimer towards CO oxidation as well as the enhanced activity of bimetallic clusters, Liu et al studied the same reaction catalyzed by Au-Ag À dimer in the gas phase and compared it with the pure Au 2 À dimer. 17 They found that anionic Au-Ag À dimer has great catalytic activity for CO oxidation and also the activity is higher compared to that of pure Au 2 À dimer. As Au-Ag À promotes CO oxidation in the gas phase, it is both natural and promising for us to investigate the catalytic activity of Au-Ag À towards NO oxidation.…”

“…Thus, the anionic clusters are appropriate for mimicking the catalytic reactivities of Au and Au-Ag nanoparticles. 17 To the best of our knowledge, no detailed theoretical or experimental studies have been reported for this reaction. In view of the potential importance and rather limited information, we carried out a detailed theoretical study on the potential energy surface (PES) of the titled reaction to (1) provide the elaborate oxidation channels;…”

CO oxidation catalyzed by silver nanoclusters: mechanism and effects of charge

“…29 Comparative studies of Au 2 À -and AuAg À -catalyzed CO oxidation found that the strong catalytic activity of AuAg À could be attributed to the synergistic effects of the Au and Ag atoms. 30 Through an investigation of the LH mechanism on Ag-NC, Jiang and co-workers found that 55-atom Ag-NC showed strong catalytic activity toward CO oxidation. 31 Kim et al studied the mechanism of 13-atom Ag-NCs-catalyzed CO oxidation, and showed that structural fluxionality accounted for the catalytic activity of small nanoparticles.…”