| Résumé | Molecular simulation is used to model the structural change of carbon nanoparticles in terms of total mass loss during the oxidation process. The density changes as well as simulation snapshots suggest a location-dependent gasification, particularly taking place in the core of the carbon particles. A graphitic shell structure of degraded carbon particles obtained from our simulations is in agreement with experimental observations. In addition, the shrinkage of graphitic crystallites near the carbon surface leads to the formation of micropores, the volume of which increases with the oxidation level. On the basis of this carbon model, the stability of Pt nanoparticles is investigated for various temperatures and roughnesses of the carbon surface. Simulation results show that migration and coalescence of Pt particles indeed occur, but at a low rate. In particular, detachment and transport of small Pt clusters were observed from simulation snapshots, supporting the argument that the transport of molecular Pt species occurs on carbon surface. The thermal activation plays a key role in the deformation of the Pt crystal structure. During simulations, both the size and surface of Pt particles increase at elevated temperature, i.e. 600 °C. However, only a few of the surface Pt atoms may contribute to the catalytic performance due to their site-dependent reactivity. |
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