particle growth at atmospheric pressure
Image courtesy of J. Catal.

Abstract

In situ aberration-corrected transmission electron microscopy, conducted in forming gas (5% H2/N2) at atmospheric pressure and elevated temperatures (up to 800 °C), was used to follow the growth of Pt nanoparticles dispersed on a high-surface-area Al2O3 support. These direct observations, facilitated by the use of monodisperse Pt nanoparticles, allowed for an unambiguous separation of the relative contributions of Ostwald ripening and particle migration/coalescence to the overall growth process and made possible the estimation of corresponding energetic and kinetic parameters. Whereas the parameters describing Ostwald ripening were as expected, the diffusion coefficient characterizing particle migration was surprisingly small. Size-selection methods were thus shown to have significant potential for suppressing Ostwald ripening, the dominant growth process, in practical catalysts.

Impact Statement

Nanoparticle catalysts are becoming increasingly important across a variety of applications. They offer high surface area, so less material is required, which reduces costs. However, the thermal stability of nanoparticle catalysts is problematic because nanoparticles tend to agglomerate into larger particles reducing their effectiveness. They usually agglomerate in one of two ways: particle migration and Oswald ripening. To better understand the agglomeration behavior (particle growth), researchers used Atmosphere to study Pt nanoparticles of various sizes supported on alumina under reducing conditions and high temperature. They found that both agglomeration processes can be limited using highly mono disperse nanoparticles.