Direct Observations of Oxygen-induced Platinum Nanoparticle Ripening Studied by In Situ TEM

TLDR

The study investigates the sintering mechanism of platinum nanoparticles on amorphous Al₂O₃, a model catalyst for automotive exhaust abatement. In situ transmission electron microscopy was used to monitor the catalyst while exposed to 10 mbar air at 650 °C. Time‑resolved TEM revealed that platinum nanoparticle sintering proceeds via Ostwald ripening, with size distributions evolving from Gaussian to log‑normal to Lifshitz–Slyozov–Wagner, and while a mean‑field kinetic model captures overall trends, individual particles show deviations due to local environmental effects.

Abstract

This study addresses the sintering mechanism of Pt nanoparticles dispersed on a planar, amorphous Al2O3 support as a model system for a catalyst for automotive exhaust abatement. By means of in situ transmission electron microscopy (TEM), the model catalyst was monitored during the exposure to 10 mbar air at 650 °C. Time-resolved image series unequivocally reveal that the sintering of Pt nanoparticles was mediated by an Ostwald ripening process. A statistical analysis of an ensemble of Pt nanoparticles shows that the particle size distributions change shape from an initial Gaussian distribution via a log-normal distribution to a Lifshitz−Slyozov−Wagner (LSW) distribution. Furthermore, the time-dependency of the ensemble-averaged particle size and particle density is determined. A mean field kinetic description captures the main trends in the observed behavior. However, at the individual nanoparticle level, deviations from the model are observed suggesting in part that the local environment influences the atom exchange process.