Catalysts are susceptible to deactivation due to poisoning or the loss of desirable structural features; encapsulation of nanoparticles has been used to inhibit poisoning and to limit the amount of inter-particle interaction. Iron and iron-containing nanoparticle catalysts are of interest as cost-effective replacements for expensive noble metal catalysts. Carbon-encapsulated (Fe@C) nanoparticles allow for investigation into the structural dynamics induced by the reaction environment and the effect of carbonaceous growth on catalyst materials. Here we report the preparation of carbon encapsulated Fe NPs catalysts and their subsequent thermal stability – degradation and coarsening. In situ transmission electron microscopy (TEM) allowed the dynamic behavior of this material to be studied during reaction, at elevated temperatures (up to 650 °C) and extended durations (minutes to hours). Under these conditions, the particles exhibited liquid-like behavior and a release of the Fe nanoparticles from their carbonaceous shells. While this behavior was primarily attributed to the increased temperatures, the energy from the electron beam likely also contributed through compression of the carbonaceous shell material, which has been shown to increase the pressure inside the core-shell considerably. Particle coarsening progressed by both Ostwald ripening and particle coalescence as competing mechanisms in parallel. In situ TEM enabled the size regimes over which ripening or particle coalescence dominated to be determined. A mechanistic understanding of the morphological evolution of the catalyst structure over the course of the reaction was developed. Because the amount of free surface area is typically correlated with activity of a nanoparticle catalyst, these results provide insight into how the activity of the system changes during reaction.

Migration and structural evolution of carbon-encapsulated Fe nanoparticles via in situ TEM

253rd National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.