Revealing particle growth mechanisms by combining high-surface-area catalysts made with monodisperse particles and electron microscopy conducted at atmospheric pressure

Abstract

In-situ aberration-corrected transmission electron microscopy, conducted in forming gas (5% H 2 /N 2) 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 Al 2 O 3 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.

Uniform synthesis of palladium species confined in a small-pore zeolite via full ion-exchange investigated by cryogenic electron microscopy

“…Such suppressed nanoparticle growth behaviour would be attributed to the conned environment by the surrounding zeolite, because our thermal treatment includes harsh reduction conditions that would otherwise cause severe Pd sintering. [47][48][49] Therefore, combining the effect of rapid nucleation and suppressed nanoparticle growth, the generation of nano-sized PdO clusters with high size-uniformity was achieved by a H 2 treatment of 5 min. Note that the rapid nucleation and size-focusing behavior is also observed from nanoparticle growth that includes a burst nucleation of monomers aer overcoming the critical monomer concentrations.…”

Adsorbate-mediated strong metal–support interactions in oxide-supported Rh catalysts

“…To directly visualize the 20CO2:2H2-induced TiO2 structural transformation, in-situ STEM analyses were performed in a closed gas cell at atmospheric pressure, as described before, 43,44 executed during reduction and 20CO2:2H2 treatment of the sintered 6% Rh/TiO2 catalyst. Following treatment at 550 ˚C in H2, conditions known to form the traditional SMSI state, a crystalline bilayer of TiOx quickly formed as a conformal coating on large crystalline Rh particles, where Ti is exclusively in the Ti 3+ oxidation state, Fig.…”

Reshaping, Intermixing, and Coarsening for Metallic Nanocrystals: Nonequilibrium Statistical Mechanical and Coarse-Grained Modeling

“…28 Instead, the issue can be resolved more directly and definitively exploiting recent advances in insitu TEM allow direct observation of catalyst evolution at elevated temperatures under working conditions. 28,30,293 We briefly describe two such studies.…”