Computational investigation of CO adsorbed on Aux, Agx and (AuAg)x nanoclusters (x = 1 \u2212 5, 147) and monometallic Au and Ag low-energy surfaces

Anna L Gould,C Richard A Catlow,Andrew J Logsdail

doi:10.1140/epjb/e2017-80280-7

Abstract

Density functional theory calculations have been performed to investigate the use of CO as a probe molecule for the determination of the structure and composition of Au, Ag and AuAg nanoparticles. For very small nanoclusters (x = 1 − 5), the CO vibrational frequencies can be directly correlated to CO adsorption strength, whereas larger 147-atom nanoparticles show a strong energetic preference for CO adsorption at a vertex position but the highest wavenumbers are for the bridge positions. We also studied CO adsorption on Au and Ag (100) and (111) surfaces, for a 1 monolayer coverage, which proves to be energetically favourable on atop only and bridge positions for Au (100) and atop for Ag (100); vibrational frequencies of the CO molecules red-shift to lower wavenumbers as a result of increased metal coordination. We conclude that CO vibrational frequencies cannot be solely relied upon in order to obtain accurate compositional analysis, but we do propose that elemental rearrangement in the core@shell nanoclusters, from Ag@Au (or Au@Ag) to an alloy, would result in a shift in the CO vibrational frequencies that indicate changes in the surface composition.

Highlights

Gold nanoclusters dispersed on metal oxide surfaces have been shown to exhibit surprisingly high catalytic activity and/or selectivity for low-temperature catalytic combustion, partial oxidation of hydrocarbons, hydrogenation of unsaturated hydrocarbons, and reduction of nitrogen oxides [1]
For AuxCO, Eads increases with nanocluster size up to x = 3, where Eads is at its greatest (–1.808 eV): the two Au atoms not directly bonded to the configuration: Eads (CO) molecule contribute charge transfer to the Au atom that is connected directly to CO, as noted by Bader analysis, leading to the formation of a stronger σ bond
We have performed theoretical calculations to determine whether CO could be used as a probe molecule for determining nanocluster structure and composition

Summary

Introduction

Gold nanoclusters (radius < 5 nm) dispersed on metal oxide surfaces have been shown to exhibit surprisingly high catalytic activity and/or selectivity for low-temperature catalytic combustion, partial oxidation of hydrocarbons, hydrogenation of unsaturated hydrocarbons, and reduction of nitrogen oxides [1]. The catalytic activity of the nanoclusters is dependent on the chosen support, preparation method, and the size of the Au nanoclusters [2].

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Conclusion