Theoretical study of CO and O2 adsorption and CO oxidation on linear-shape gold molecules (LGMn) (n=2, 4, 8, 16, and 24)

Tetsuya Ohkawa,Kei Kuramoto

doi:10.1063/1.4962824

Abstract

Density functional theory is used to study the effect of increase of the number of Au atom in the adsorption of CO and O2 as well as CO oxidation on anionic, neutral, and cationic Linear-shape Gold Molecules (LGMn) (n=2, 4, 8, 16, and 24). The more the number of Au atom increases, the more the adsorption energies of CO lower and larger in the cationic and anionic LGMnCO complexes, respectively. In contrast, the adsorption energies of both CO and O2 on neutral LGMn exhibit approximately constant values. There are little differences of both adsorption energies and net charge of CO and O2 on the number of Au atom in LGM regardless of each charge state. This indicates that the charge state of LGM plays a less important role for the adsorption of CO and O2 with increase of the number of Au atom in LGM. The trend of the overall activation energies of reaction pathway is switched between LGM4−1 and LGM8−1 with increase of the number of Au atom in LGM, and OC-OO intermediate of the initial state in LGMn−1 (n=8, 16, and 24) are unstable compared to the separated reactants (LGMn, CO, O2). These are caused by the values of charge of O2 of OC-OO intermediate.

Highlights

Au has attracted much attention in recent years since the high activity of Au nanoparticles was reported by Haruta et al.[1]
O2 of OC-OO in small LGMnO2 complexes are decreased from 0.380 (LGM2)−1 and LGM4−1 are bound and stable because they are charge transferred from Au atoms in LGM-1, but O2 of OC-OO in large LGM-1 are unstable because its charge values are smaller than those in small LGM-1 and the charge transfer is switched from Au atoms in LGM-1 to CO
We performed density functional theory (DFT) calculation for CO oxidation to investigate the effect of increase of the number of Au atom in LGMn (n=2, 4, 8, 16, and 24) and charge state of LGMn

Summary

Introduction

Au has attracted much attention in recent years since the high activity of Au nanoparticles was reported by Haruta et al.[1] When Au is highly dispersed on oxide support, it can exhibit surprisingly high catalytic activity. The important factors that Au exhibits extraordinary catalytic activity have been investigated These factors include the size of Au nanoparticles,[8,9,10,11,12] the electronic state and fluxionality of Au clusters,[13,14,15,16] and type and structure of oxide supports.[10,13,16,17,18] in spite of their exceptional effort, the dominant factors are still under investigation and are studied extensively

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Results

Conclusion