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Gold clusters of nanometer size are known to act as catalysts of the oxidation of CO (Haruta et al.). The catalytic activity of these particles has been shown to strongly depend on the size of their size (Goodman et al.). However, the in situ measurements of the particle diameters that are commonly performed by near field microscopy suffer from tip artifact. The present work reports on an attempt to study in situ gold clusters of 1 to 5 nm deposited on TiO2(110). Analyses were performed either in vacuum or during the catalytic oxidation of CO at room temperature by Grazing Incidence X-ray Scattering (GIXS, large angles) and Grazing Incidence Small Angle X-ray Scattering (GISAXS), on beam-line BM 32 at ESRF facility (Grenoble). The oxidation reaction was run for oxygen and CO partial pressures of 2000 Pa and 10 to 100 Pa, respectively. It was analyzed via a controlled leak toward a mass spectrometer. By recording GIXS diffraction patterns and GISAXS images, the average size of the particles could be correlated with the Au-Au distance within the particles. Further, these parameters could be associated to the reactivity of the particles. The oxygen alone had no visible effect on the GISAXS image of the gold particles. Instead, the presence of either a partial pressure of CO or a reactive mixture of CO + O2 resulted in a change in size of the particles that could be analyzed by GISAXS. The capability of the set up to simultaneously analyse the crystallography, the size and the reactivity of supported gold particles is demonstrated. The values determined herein are discussed with respect to the measurements already performed by near-field microscopy. |