| AVS 57th International Symposium & Exhibition | |
| Surface Science | Monday Sessions |
| Session SS1-MoA |
| Session: | Nanocluster Reactivity |
| Presenter: | J. Jupille, Inst. des Nanosciences de Paris, France |
| Authors: | J. Jupille, Inst. des Nanosciences de Paris, France M.-C. Saint-Lager, Inst. Néel, France A. Bailly, Inst. Néel, France G. Cabailh, Inst. des Nanosciences de Paris, France S. Garaudée, Inst. Néel, France R. Lazzari, Inst. des Nanosciences de Paris, France P. Dolle, Inst. Néel, France O. Robach, CEA, France I. Laoufi, Inst. Néel, France H. Cruguel, Inst. des Nanosciences de Paris, France |
| Correspondent: | Click to Email |
The catalytic activity of supported gold nanoparticles [1] has generated great excitement over the two last decades. In contrast with the inertness of the bulk gold, the catalytic activity of gold nanoparticles increases dramatically as their size decreases. Most studies have focused on the catalytic oxidation of CO in particular because gold catalyzes that reaction at temperature as low as 200 K with an even better activity than platinum [2]. The origin of the property is still debated. Following the earlier suggestion that reactive sites are at the edge of the Au/oxide interface [2], it was alternatively proposed from density functional approaches, in the frame of a pure gold pathway, that the activity of gold nanoparticles mostly comes from low coordinated atoms [3]. In a very different manner, the activity of gold nanoparticles was attributed to a quantum size effect with a maximum in activity for two-atom-thick clusters [4].
To date, a direct characterization of the morphology of gold nanoclusters during catalytic reactions is lacking. The present works reports on observations by Grazing Incidence Small Angle X-Ray Scattering (GISAXS) of Au/TiO2(110) supported particles during the catalytic oxidation of CO, by using a dedicated set up. The analysis chamber, operated from ultra-high vacuum to normal pressure, is acting as a reactor [5]. The reactivity is determined by mass spectrometry. In the present case (20 mbar O2 + 0.1 mbar CO on Au/TiO2(110) at 200 K), it rapidly increases for particles < 5 nm. GISAXS demonstrates that reacting gold particles are always three-dimensional with an aspect ratio H/D ≈ 0.6 (H and D are the height and diameter of the particles, respectively) which, for the smallest particles under study (D = 2 nm) still corresponds to 4 atomic layers of gold. The reaction mechanism is discussed via the relationship between the reactivity and the particle geometry.
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[3] I. N. Remediakis et al., Angew. Chem. Int. Ed. 44 (2005) 1824.
[4] M. Valden et al., Science 281 (1998) 1647.
[5] M.-C. Saint-Lager et al., Rev. Sci. Instrum. 78 (2007) 083902.