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Adsorption energetics of CO on supported Pd nanoparticles as a function of particle size by single crystal microcalorimetry

MPS-Authors
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Flores Camacho,  Jose Manuel
Chemical Physics, Fritz Haber Institute, Max Planck Society;

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Fischer-Wolfarth,  Jan-Henrik
Chemical Physics, Fritz Haber Institute, Max Planck Society;

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Peter,  Matthias
Chemical Physics, Fritz Haber Institute, Max Planck Society;

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Schauermann,  Swetlana
Chemical Physics, Fritz Haber Institute, Max Planck Society;

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Freund,  Hans-Joachim
Chemical Physics, Fritz Haber Institute, Max Planck Society;

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c1cp21677e.pdf
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Citation

Flores Camacho, J. M., Fischer-Wolfarth, J.-H., Peter, M., Campbell, C. T., Schauermann, S., & Freund, H.-J. (2011). Adsorption energetics of CO on supported Pd nanoparticles as a function of particle size by single crystal microcalorimetry. Physical Chemistry Chemical Physics, 13(37), 16800-16810. doi:10.1039/c1cp21677e.


Cite as: http://hdl.handle.net/11858/00-001M-0000-000F-00E2-1
Abstract
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 8 for the smallest 1.8 nm sized particles and by 1.4 for the particles of 7–8 nm size.