Magic-Number Gold Nanoclusters with Diameters from 1 to 3.5 nm: Relative Stability and Catalytic Activity for CO Oxidation

Abstract

Relative stability of geometric magic-number gold nanoclusters with high point-group symmetry ((Ih), D(5h), O(h)) and size up to 3.5 nm, as well as structures obtained by global optimization using an empirical potential, is investigated using density functional theory (DFT) calculations. Among high-symmetry nanoclusters, our calculations suggest that from Au(147) to Au(923), the stability follows the order Ih > D(5h) > Oh. However, at the largest size of Au(923), the computed cohesive energy differences among high-symmetry I(h), D(5h) and O(h) isomers are less than 4 meV/atom (at PBE level of theory), suggesting the larger high-symmetry clusters are similar in stability. This conclusion supports a recent experimental demonstration of controlling morphologies of high-symmetry Au(923) clusters ( Plant, S. R.; Cao, L.; Palmer, R. E. J. Am. Chem. Soc. 2014, 136, 7559). Moreover, at and beyond the size of Au(549), the face-centered cubic-(FCC)-based structure appears to be slightly more stable than the Ih structure with comparable size, consistent with experimental observations. Also, for the Au clusters with the size below or near Au(561), reconstructed icosahedral and decahedral clusters with lower symmetry are slightly more stable than the corresponding high-symmetry isomers. Catalytic activities of both high-symmetry and reconstructed I(h)-Au(147) and both Ih-Au(309) clusters are examined. CO adsorption on Au(309) exhibits less sensitivity on the edge and vertex sites compared to Au(147), whereas the CO/O2 coadsorption is still energetically favorable on both gold nanoclusters. Computed activation barriers for CO oxidation are typically around 0.2 eV, suggesting that the gold nanoclusters of ∼ 2 nm in size are highly effective catalysts for CO oxidation.

Kinetic Monte Carlo approach to Schottky defects in noble metal nanoclusters

“…These results indicate that any central vacancy with bulk coordination would behave the same, since this model only takes into account the coordination of the site. This is in contrast to some recent DFT studies, where accounting for strain effects show that a central vacancy may be energetically favored [37]. The data in both figures shows that the energy associated with creating a vacancy depends on the physical parameters of the metals, and for the noble metals goes in order of gold, copper and silver, from largest to smallest.…”

Atomistic simulations of nanoscale tungsten clusters: From structure and energetics to melting properties

“…Fig. 1 shows that the average potential energy per atom decreases with increasing cluster size due to the decrease of surface area to volume ratio, which is consistent with recent atomistic simulations on metallic clusters [19]. For cluster sizes of N 6 15, cluster configurations determined by the two methods are the same.…”

“…Over the past several decades, a large body of atomistic simulations on clusters (especially metallic clusters) has been performed using Finnis-Sinclair potentials [13,14], embedded-atom method (EAM) potentials [15,16], tight-binding method potentials [15,17] and first-principles calculations based on density functional theory (DFT) [18,19] to explore their structure and energetic stability, growth, interaction with surfaces, phase transitions, strain and surface energies, melting and freezing behaviors.…”

Nanocluster structure deduced from AC-STEM images coupled to theoretical modelling

“…While, for example, gold crystallizes in the face centered cubic (FCC) structure, small Au clusters can have very different atomic ordering by forming, for example, icosahedral or decahedral structures with fivefold symmetry (see, for example, Ref. [4]) Various theoretical calculations have addressed this problem, using mainly empirical potential functions to describe the interaction between the Au atoms, electronic density functional theory (DFT), or a combinations of both. But, it is extremely hard to search for the optimal structure of such a cluster even if it contains only ca.…”