Gold nanoparticles supported on different oxides (SiO 2 , CeO 2 and TiO 2 ) were prepared by the SMAD (solvated metal atom dispersion) and deposition-precipitation (DP) techniques. The physical and chemical characterization of the catalysts was performed by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) and the catalytic activity was tested during the reaction of low temperature CO oxidation. The structural and surface analyses evidenced the presence of small gold crystallites (cluster size ∼2-5 nm) in all the SMAD-prepared samples and oxidized gold species in the case of the DP catalysts. A different surface distribution of ionic gold species was found on the different supports. By comparing the catalytic activities of the samples, the presence of Au +1 species seems to be the main requisite for the achievement of the highest CO conversion at the lowest temperature. The higher activity of Au/CeO 2 (DP) catalysts at T ≈ 250 K can be ascribed to a better stabilization of the AuO − species by the cerium oxide. Nanosized metallic gold particles exhibit a worse catalytic performance, both on 'reducible' and 'inert' supports, being significantly active only in the temperature range: 400-600 K.

Gold catalysts supported on cerium oxide were prepared by solvated metal atom dispersion (SMAD), by deposition-precipitation (DP), and by coprecipitation (CP) methods and were characterized by X-ray diffraction (XRD), temperature programmed reduction (TPR), and X-ray photoelectron spectroscopy (XPS). The catalytic activity was tested in the CO oxidation reaction. The structural and surface analyses evidenced the presence of a modified ceria phase in the case of the DP sample and the presence of pure ceria and gold metal crystallites in the case of the SMAD and CP samples. The DP sample, after a mild treatment in air at 393 K, exhibited only ionic gold, and it was very active below 273 K. By comparing the activities of the different catalysts, it is suggested that the presence of small gold particles, as obtained by the SMAD technique, is not the main requisite for the achievement of the highest CO conversion. The strong interaction between ionic gold and ceria, by enhancing the ceria surface oxygen reducibility, may determine the particularly high activity.

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