Revealing Dispersion Processes in Ag Nanoclusters with In Situ NAP Studies
Identifying the dispersion mechanism of Ag nanoclusters with the EnviroESCA and the NAP PEEM.
Sintering, i.e. agglomeration, of metal catalyst particles during their use at elevated temperatures is a process which limits performance of those catalysts since it reduces active surface area. This detrimental mechanism can often be compensated by oxygen induced dispersion of the agglomerated particles. This process was widely accepted to be driven by mobile metal oxides on the clusters. Using the EnviroESCA, the newly developed NAP PEEM and in situ environmental TEM, Li et al. from the group of Fu Qiang from DICP in Dalian, China, were able to identify the intermediate steps and reaction path, responsible for the dispersion of metallic particles in oxygen atmosphere.
Starting with Ag Nanowires, the dispersion into Ag particles from nanometer size and their oxidation was followed in detail using in situ analysis. The process was reversible as the formation of Ag oxides and larger agglomerates of Ag could be traced. The finding was that the particle dispersion is adsorption induced and driven by a nearly metallic state of Ag, followed by oxidation and stabilization after the dispersion, rather than being driven by the formation of oxidized nanoparticles.
This analytically outstanding study combines several state of the art techniques operating at elevated pressure to understand the adsorption mechanism leading to the observed effect. The EnviroESCA was used to determine the spectroscopic fingerprint of the reaction steps, while the microscopic methods NAP-PEEM and Environmental TEM where used to characterize the appearance of the nanoparticles on the samples in situ.