How the Facet Edge Controls the Overall CO Oxidation in Nanoporous Gold: Combined Atomistic Characterization/DFT Study of Residual Ag Distribution and Catalytic Activity

Abstract

Nanoporous gold (NPG) formed via dealloying/selective dissolution of the Au−Ag alloy is known to be catalytically active toward CO oxidation reaction (COR) even at room temperature. The atomistically resolved NPG structure is obtained by simulating the dealloying of Au25Ag75 nanoparticles using a combination of kinetic Monte Carlo and molecular dynamics. The effect of adsorbed O is included. The experiment-like NPG structures from these computer simulations are characterized. We map the surface of NPG, determine the diverse binding sites, and assess their role in catalysing the COR. Local surface Ag composition, population density of undercoordinated Au/Ag atoms, and cluster size distribution of surface Ag atoms are measured. A high density of dislocation defects is found in the simulated structure. The rate-determining steps, namely, O2 binding and dissociation, are probed using density functional theory. We conclude that O2 binding/dissociation is facilitated at the facet edge. Residual Ag at the edge aids in the capture of O2. Subsequently, O2 dissociates after spilling over to Au sites at the facet edge. These conclusions are confirmed by showing that the normalized facet edge length of NPG and supported Au nanoparticles is linearly correlated to the experimental turnover frequency.Keywords: nanoporous gold, dealloying, CO oxidation, elemental distribution, density functional theory, molecular dynamics, Monte CarloFigure : Dealloying of Au-Ag NP to get NPG which has high catalytic activity for COR Figure 1