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

Abstract

This study addresses the sintering mechanism of Pt nanoparticles dispersed on a planar, amorphous Al(2)O(3) 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 degrees 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.

Understanding the electrocatalysis of oxygen reduction on platinum and its alloys

“…For instance, one could anticipate that ''Pt-skin'' nanoparticles should exhibit improved activity over Pt in comparison to ''Pt-skeleton'' nanoparticles. However, surface impurities, surface segregation of the solute metal, 160 sintering, 166 and degradation of the carbon support 167 all complicate the annealing process on nanoparticles. Nonetheless, several research groups have reported the synthesis of ''Pt-skin'' structures upon carbon-supported Pt-alloy nanoparticles.…”

Atomistic Theory of Ostwald Ripening and Disintegration of Supported Metal Particles under Reaction Conditions

“…This highlights the importance of the in situ study on the sintering kinetics, as well documented in the literature. 26,46,47,74 Journal of the American Chemical Society 2.4. Reactant Induced Disintegration.…”

Exploring the environmental transmission electron microscope

“…As discussed above, environmental studies can be performed in an ETEM with the use of conventional sample holders (Hansen et al, 2001;Helveg et al, 2004;Kim et al, 2010;Simonsen et al, 2010) or in a traditional TEM by use of a dedicated sample holder with a high pressure cell (Creemer et al, 2008). In both cases the setup defines the boundary conditions regarding gas, pressure and temperature.…”