Abstract
We have studied the oxidation of MgO(100) supported Pd nanoparticles in a size range from at and near atmospheric pressures. Our experimental setup using high-energy x rays allows us to study in situ the oxidation behavior for different particle sizes under identical experimental conditions. We can identify three size regimes with a distinct oxidation mechanism. For particles smaller than in diameter, kinetic barriers for bulk oxide formation are strongly reduced and complete transformation to PdO bulk oxide takes place, epitaxial to the MgO substrate. Particles with a diameter undergo continuous shrinkage during oxidation accompanied by the formation of epitaxial PdO on MgO(100). For larger particles with , we observe a complete passivation of the particle surface by a thin polycrystalline PdO layer, which prevents further oxidation. Our experiments demonstrate that particles with a few nanometers in size exhibit a much higher reactivity with oxygen, which is important for the performance of Pd nanoparticles as a CO oxidation catalyst.
1 More- Received 6 September 2007
DOI:https://doi.org/10.1103/PhysRevB.77.115444
©2008 American Physical Society