Metal nanocrystals: Deforming like liquid droplets

Probing the H2-Induced Restructuring of Pt Nanoclusters by H2-TPD

Metal clusters with sizes below 1 nm attract great scientific interest, but the main information on their properties still comes from quantum mechanics modeling and costly physical methods of limited availability. We have studied ultradispersed Pt/γ-Al₂O₃ samples with temperature-programmed desorption (TPD) and complementary adsorption/desorption techniques and observed that the H₂-TPD profile of Pt/γ-Al₂O₃ is strongly dependent on the pretreatment conditions (0 < P_H2 ≤ 1 bar; 200 K ≤ T ≤ 470 K). The results corroborate recent theoretical and spectroscopic studies predicting alterations in the structure of Pt nanoclusters under H₂-treatment conditions but reveal that the restructuring needs to overcome continuous activation barriers and leads both to an increase in surface coverage and strengthening of the Pt-H bonds. This was interpreted as being a consequence of the strong interaction of Pt clusters with the support. The results extend insights into the behavior of supported metal particles and expand the potential of existing experimental techniques.

Molecular dynamics simulations of the atom packing characteristics of three deformed silver nanoparticles at room temperature

Deformation is of significance in controlling the shape of materials, but the key structural information of metal nanoparticles is still limited. Molecular dynamics simulations are performed to explore the microscopic details of atom packing differences in three deformed silver nanoparticles with one atom difference. Analytical tools are used to demonstrate the effects of external load and surface atoms of particles on the packing patterns in these deformed nanoparticles including internal energy per atom, pair numbers, and pair distribution functions as well as cross-sectional images. The simulation results show that under small compression, the particles present elastic behaviors. The increasing compression results in the sliding of the atoms in different parts of these particles, and some interfaces are formed between these parts. As the external load becomes large, these deformed particles are compressed into the thickness of several atomic layers. The unloaded particles present different behaviors.