In situ identification of the metallic state of Ag nanoclusters in oxidative dispersion

Abstract

Oxidative dispersion has been widely used in regeneration of sintered metal catalysts and fabrication of single atom catalysts, which is attributed to an oxidation-induced dispersion mechanism. However, the interplay of gas-metal-support interaction in the dispersion processes, especially the gas-metal interaction has not been well illustrated. Here, we show dynamic dispersion of silver nanostructures on silicon nitride surface under reducing/oxidizing conditions and during carbon monoxide oxidation reaction. Utilizing environmental scanning (transmission) electron microscopy and near-ambient pressure photoelectron spectroscopy/photoemission electron microscopy, we unravel a new adsorption-induced dispersion mechanism in such a typical oxidative dispersion process. The strong gas-metal interaction achieved by chemisorption of oxygen on nearly-metallic silver nanoclusters is the internal driving force for dispersion. In situ observations show that the dispersed nearly-metallic silver nanoclusters are oxidized upon cooling in oxygen atmosphere, which could mislead to the understanding of oxidation-induced dispersion. We further understand the oxidative dispersion mechanism from the view of dynamic equilibrium taking temperature and gas pressure into account, which should be applied to many other metals such as gold, copper, palladium, etc. and other reaction conditions.

Image processing with a multi-level ultra-fast three dimensionally integrated perovskite nanowire array

“…S7b (ESI †), the binding energy peak positions of Ag (3d), Bi (4f) and I (3d) at 368.4 eV, 158.2 eV and 622.2 eV for a MBI PNW device matches well with previous reports, affirming the material integrity of the device during the XPS study. [32][33][34] The intensity vs. binding energy plots, corresponding to Ag (3d), for the PNW and SNW devices are provided in Fig. S8 of the ESI.…”

“…The peak positions of the Ag (3d) binding energy for the PNW match very well with those of metallic bulk Ag as confirmed from previous reports. 32 On the other hand, the upshift observed at the Ag/MBI NW interface for the SNW is an indication of the size effect coming into play rather than a change in the oxidation state of Ag which is traditionally associated with a downshift of the binding energy. 32,35,36 More precisely, this interesting result indicates that, at the interface and inside the SNW, there are plausible nanoclusters (NCs) of Ag rather than a continuous bulk metal thin film.…”

Regulating the Tip Effect on Single‐Atom and Cluster Catalysts: Forming Reversible Oxygen Species with High Efficiency in Chlorine Evolution Reaction

“…It can be realized by modifying the TE of the active center, which is related with electronic metal‐support interaction (EMSI) [30, 31] . And the oxidized sub‐nano cluster catalysts (OSCCs) provide perfect platforms to carry out the modification of the TE [32–42] …”

Insights into structure of metal nanomaterials in reactive environments

“…Although the oxidative dispersion has been accepted as the general mechanism for generating the nanoclusters and single atoms, a recent experiment indicated the chemisorption of oxygen on metal rather than oxidation can be the driving force for dispersing metal clusters and stabilizing ultra‐small metal clusters in the oxidative conditions. Li et al 74 showed the dynamic dispersion of Ag nanowires into Ag clusters on Si 3 N 4 surface under O 2 environment. As shown in Figure 7, silver nanowires were highly dispersed driven by the combined effects of the metal–substrate interaction and the stronger adsorption of O 2 on Ag nanoclusters.…”

“…(a) Dynamic evolution of Ag nanowires during oxidative dispersion. (b) The formation energy of Ag 3 and Ag 8 cluster based on the Ag particle under different influencing factors (reprinted with permission from Reference [74], Copyright 2021 Springer Nature)…”