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

Abstract

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...