Effect of phase and size on surface sites in cobalt nanoparticles
R Agrawal and P Phatak and L Spanu, CATALYSIS TODAY, 312, 174-180 (2018).
Molecular dynamics was applied to simulate cobalt nanoparticles to understand the effects of particles size and crystal phases on the distribution of surfaces sites relevant for Fischer-Tropsch catalysis. The results indicate a minimal change (<5%) in the coordination number distribution of surface atoms for particles larger than 4 nm even at 500 K, implying that temperature is not sufficient to drive surface reconstruction. We found that the distribution of B5 sites differ significantly between hcp and fcc particles, suggesting different CO adsorption properties for the two phases. HCP particles offer different types of B5 sites which are sterically less hindered for CO adsorption and maybe the reason for differences in catalytic behaviors of hcp vs. fcc nanoparticles. Finally, the smaller nanoparticles have higher radial contraction on the surface, which could impact the deactivation mechanism of these particles by inhibiting the sub-surface diffusion of adsorbate species.
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