期刊
PHYSICAL CHEMISTRY CHEMICAL PHYSICS
卷 13, 期 37, 页码 16800-16810出版社
ROYAL SOC CHEMISTRY
DOI: 10.1039/c1cp21677e
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资金
- German Science Foundation (DFG) [546]
- Cluster of Excellence Unifying concepts in catalysis (UNICAT)
- Robert-Bosch-Stiftung
- US DOE, OBES Chemical Sciences [DE-FG02-96ER14630]
The heat of adsorption and sticking probability of CO on well-defined Pd nanoparticles were measured as a function of particle size using single crystal adsorption microcalorimetry. Pd particles of different average sizes ranging from 120 to 4900 atoms per particle (or from 1.8 to 8 nm) and Pd(111) were used that were supported on a model in situ grown Fe3O4/Pt(111) oxide film. To precisely quantify the adsorption energies, the reflectivities of the investigated model surfaces were measured as a function of the thickness of the Fe3O4 oxide layer and the amount of deposited Pd. A substantial decrease of the binding energy of CO was found with decreasing particle size. Initial heat of adsorption obtained on the virtually adsorbate-free surface was observed to be reduced by about 20-40 kJ mol(-1) on the smallest 1.8 nm sized Pd particles as compared to the larger Pd clusters and the extended Pd(111) single crystal surface. This effect is discussed in terms of the size-dependent properties of the Pd nanoparticles. The CO adsorption kinetics indicates a strong enhancement of the adsorbate flux onto the metal particles due to a capture zone effect, which involves trapping of adsorbates on the support and diffusion to metal clusters. The CO adsorption rate was found to be enhanced by a factor of similar to 8 for the smallest 1.8 nm sized particles and by similar to 1.4 for the particles of 7-8 nm size.
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