Insights from Theory on the Relationship Between Surface Reactivity and Gold Atom Release

Abstract

Density functional theory, informed by experimental studies, is used to investigate the interplay of surface morphology, the adsorption site of reactants, the nature of the interaction between adsorbates and the surface, the potential energy landscape for adsorbates on the surface, adsorbate coverage, temperature, and the dynamic evolution of these factors during adsorption and reaction. We summarize our current understanding of Au atom release on the (111) surface and the corresponding effects on adsorption and reactivity. Gold was selected for these investigations because of the recent intense interest in the activity of gold nanoparticles for several important catalytic reactions. Fundamental experimental studies on Au single-crystal surfaces have established that atomic O is extremely active for oxidation of CO and olefins, that the local bonding of O is an important factor in determining the reactivity and selectivity for oxidation, and that Au atom release is induced by electronegative adsorbates, such as O, Cl, and S. These experimental results guided our theoretical studies. Density functional theory is an extremely useful tool since it evaluates the energetics associated with the incorporation of gold into the adsorbate layer, while providing fundamental physical insight into the underlying cause of gold incorporation. We use our results from static DFT calculations along with ab initio molecular dynamics simulations to understand the effect of surface morphology on the activity of gold for CO oxidation. Our investigation of Au atom release and incorporation induced by electronegative atoms clearly illustrates the importance of using experiments in combination with theory to establish the importance of and the underlying reasons for metal atom release and the affect on bonding and reactivity.

Trapping of Charged Gold Adatoms by Dimethyl Sulfoxide on a Gold Surface

“…37,67,68 Moreover, it is also well established that molecular adsorption, especially involving very electronegative species, can significantly promote such processes. 37, 69 In contrast to thiols and other molecules that interact strongly with gold, in our case no lifting of the herringbone reconstruction was ever observed, likely because the interaction of DMSO with gold is comparatively weaker (no covalent bonding occurs between the molecule and the metal). 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 indicates the energy gain per DMSO molecule in the most stable adso...…”

Manipulating the Conformation of Single Organometallic Chains on Au(111)

“…57 Of particular interest to this work is the more general observation that the adsorption of electronegative elements, such as the halogen chlorine, 56 give rise to the release of gold atoms from the herringbone reconstruction of the Au(111) surface, with the released atoms being incorporated into the adsorbate structure. 53 In our experimental data we observe a lifting of the herringbone reconstruction in the vicinity of the linear chains (shown in the STM image in Figure 2a -see also Supporting Information)…”

Paracrystalline structure of gold, silver, palladium and platinum nanoparticles

“…In the old Taylor concept of 'active sites', it was assumed that the catalytic activity of the surface is conditioned by the nature of the arrangement and the spacing of the atoms in the surface layer (Taylor, 1925). This idea has been recently developed using HRTEM observations accompanied by density functional theory simulations (Johnson et al, 2008;Baker et al, 2010;Chang et al, 2010;Stenlid & Brinck, 2017). From this work it has been concluded that the catalytic activity of the noble metal nanoparticles can be understood by assuming the defective and strained nature of their surface structure.…”