Rutile-Supported Ir, Au, and Ir−Au Catalysts for CO Oxidation

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• 作者：Xim Bokhimi ; Rodolfo Zanella ; Carlos Angeles-Chavez
• 刊名：Journal of Physical Chemistry C
• 出版年：2010
• 出版时间：August 26, 2010
• 年：2010
• 卷：114
• 期：33
• 页码：14101-14109
• 全文大小：525K
• 年卷期：v.114,no.33(August 26, 2010)
• ISSN：1932-7455

文摘

Ir/rutile, Au/rutile, and Ir−Au/rutile catalysts were synthesized at 80 °C and activated at 300, 400, or 500 °C in hydrogen. These catalysts were analyzed with X-ray powder diffraction and refinement of the crystalline structures as well as with high-resolution electron microscopy and infrared spectroscopy. They were used to catalyze the oxidation of CO: Ir/rutile catalysts started their catalytic activity above 50 °C, whereas Au/rutile and Ir−Au/rutile catalysts were active for this reaction even below room temperature. The catalysts containing both iridium and gold were the most active; these catalysts consisted of small and large metallic crystallites supported on rutile. The small crystallites, which contained iridium or iridium and gold, had the morphology of a cuboctahedron and dimensions near 1 nm; the large ones contained only gold. The small crystallites, based on iridium, were very stable because iridium oxide has the same crystalline structure as the support, rutile. In contrast, the local atom distribution of gold oxide is incompatible with the crystalline structure of rutile; therefore, the metallic gold crystallites grew differently: they grew on the defects of the support, which produced crystallites with dimensions between 2 and 3 nm. The improvement of the catalytic activity for the oxidation of CO of Ir−Au/rutile catalysts, in comparison with Au/rutile catalysts, could be due to a synergetic effect caused by the combination of gold and iridium in the small particles. Time aging of these catalysts showed that they adsorbed carbonates on active sites, which decreased their catalytic activity. This activity, however, was recovered after removing the carbonates by heating the catalyst in air and then in hydrogen at 300 °C.