Evolution of Carbon Nanofiber-Supported Pt Nanoparticles of Different Particle Sizes: A Molecular Dynamics Study

Molecular
dynamics simulations employing the ReaxFF reactive force field have
been carried out to analyze the structural evolution of fishbone-type
carbon nanofiber-supported Pt nanoparticles, with particle size ranging
from 5.6 to 30.7 Å. Simulated results indicate that upon adsorption
the distribution of first-shell Pt–Pt coordination number and
radial distribution function change significantly in Pt nanoparticles
up to 2 nm in size and that the restructuring degree of the Pt nanoparticles
decreases with particle size, which is attributed both to the reduced
binding energy per Pt atom bonded to support and to the increased
cohesive energy of the Pt nanoparticles. In the Pt10 particle,
the majority of the Pt atoms are detached from the metal particle,
leading to atomic adsorption of single Pt atoms on the support. As
the Pt particle size is increased to ∼3 nm, however, the crystalline
degree of Pt nanoparticles is even higher than that of the corresponding
isolated nanoparticles because the strong metal–support interaction
has a positive effect on the crystalline degree of the upper part
of Pt nanoparticles. Two surface properties of the Pt nanoparticles,
namely, Pt dispersion and coordination number of surface Pt atoms,
are then computed and found to decrease and increase, respectively,
with particle size. Thus, on-purpose control of particle size (and
hence the metal–metal and metal–support interactions)
is of crucial importance for tuning the superficial structures of
supported active metal particles, which eventually determine the adsorption
and catalytic properties of catalysts.