COLL 353 |
| At elevated temperatures, the vapor pressure of small metal particles can be orders of magnitude higher than that of the bulk metal. While the effect of reduced dimensionality on changing the properties of nanoparticles, such as melting point and band gap, is well known, it has not commonly been applied to catalytic nanoparticles at the relatively high temperatures (e.g., 850 °C), such as those required for hydrogen producing thermochemical cycles. At these temperatures, Pt nanoparticles less than about 5 nm sublime orders of magnitude faster than expected based on bulk properties. This effect, in conjunction with surface diffusion, can be a significant factor in catalyst deactivation. First principles, density functional theory calculations of the heat of vaporization show that nanoparticle vapor pressures increase exponentially with the inverse of the particle diameter. This effect is not confined to Pt, but is found in other metal nanoparticles, most at substantially lower temperatures. |
|
Surface Chemistry Symposium in Honor of Gabor Somorjai
8:30 AM-11:50 AM, Tuesday, 12 September 2006 Sir Francis Drake -- Franciscan Room, Oral
Division of Colloid & Surface Chemistry |