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Shape and surface structure of gold nanoparticles under oxidizing conditions

We perform density-functional theory calculations to investigate the adsorption of oxygen at the Au100 and Au110 surfaces. For the clean surfaces, we find that the added-row 51 /Au100 structure is more stable than the unreconstructed 11 /Au100 surface and the missing-row 21 /Au110 structure is more stable than the unreconstructed 11 /Au110 surface, which is consistent with experimental results. For oxygen adsorption on Au100, the most stable structure is predicted to be a low coverage 0.1 ML on the added-row reconstructed surface, while for adsorption on Au110, the most stable configuration of those considered is a 21 missing-row structure with 1 ML coverage of oxygen. From these results, together with those of our previous investigations into the O /Au111 system, we use the Wulff construction to predict the nanoparticle shape as a function of oxygen chemical potential, which we correlate with pressure p and temperature T. For low values of the oxygen chemical potential 0.6 eV, corresponding, e.g., to p =1 atm and T600 K, the nanoparticle consists of clean 111 facets. For slightly higher values, clean 111 facets still dominate but there are small regions of 110 facets, which are covered with the 21-2O reconstruction. With progressively increasing values of the chemical potential e.g., from 0.4 to 0.18 eV, corresponding to, e.g., p=1 atm and T=420‐200 K, the 111 facets become covered with a thin oxide-like structure, and the 110 regions with the 212O/110 surface reconstruction become larger and finally dominate. These findings indicate that for low temperature oxidation reactions, where gold nanoparticles have been reported to be surprisingly active, such thin “surface-oxide-like” structures on the 111 and 110 surfaces could possibly play a role in the behavior of the nanogold catalysts.