PHYS 8 |
| The changes in the electronic structure and surface composition of monodispersed cobalt nanoparticles with different sizes have been followed using in situ spectroscopy techniques in the Advance Light Source (Berkeley), X-ray absorption spectroscopy (XAS) and high pressure photoelectron spectroscopy (HPPS). Their catalytic performance in the carbon monoxide hydrogenation reaction has been tested also in a fixed bed reactor. The nanoparticles have been synthesized by colloidal chemistry and supported over a flat support (gold foil) by the Langmuir-Blodgett technique, obtaining an ideal 2-D model of a cobalt catalyst, as shown by scanning electron microscopy (Figure 1). The as-synthesized particles are in the metallic state, but they oxidize to CoO during the cleaning and transferring procedure. A specially designed gas-flow cell was used in order to perform in situ XAS measurements. This cell allows us to work in atmospheric pressure and to follow simultaneously the Co L-edge and O K-edge of the cobalt nanoparticles. The treatment of the samples in pure hydrogen at temperatures up to 350ºC causes the reduction of the cobalt oxide and the removal of the surfactant layer covering the particles, as evidenced by O K-edge spectra in XAS. These results have been further confirmed by high pressure XPS. The scanning electron microscopy pictures of the samples after the reducing treatments show that the morphology of the samples has not been changed (Figure 1). The catalytic performance reveals that the samples become active after the reduction treatment and that they are significantly more resistant to deactivation than a standard sample. Their reactivity is different depending on the Co particle size.
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Nanostructured Materials
8:10 AM-12:00 PM, Sunday, April 6, 2008 Morial Convention Center -- Rm. 338/339, Oral
Division of Physical Chemistry |
