In-Situ DRIFT Study of Au–Ir/Ceria Catalysts: Activity and Stability for CO Oxidation

Monometallic gold and iridium, and bimetallic gold–iridium on ceria catalysts were synthesized by deposition–precipitation with urea. The activity of these ceria supported catalysts for CO oxidation was: Au–Ir ≫ Au > Ir. The bimetallic catalyst was highly active and stable during the carbon monoxide oxidation reaction, showing synergism between both metals. The catalysts were thoroughly characterized chemical and structurally. High-resolution electron microscopy coupled with energy dispersive spectroscopy and X-ray photoelectron spectroscopy showed evidences of iridium–gold intimacy. In situ infrared spectroscopy in the diffuse reflectance mode was used to investigate the reactivity of the active sites. Concentration-modulation excitation spectroscopy allowed selective identification of intermediates and ‘spectator’ species. CO chemisorbed onto iridium sites (2096, 2060 and 2012 cm−1) was found inactive, whereas carbon monoxide on metallic gold sites (Au0–CO, 2110 cm−1) exhibited reactivity for CO oxidation. In the bimetallic catalyst, new active sites (Auδ−–CO, 2095 and 2026 cm−1) together with Au0–CO species were observed, most likely produced by the isolation and stabilization of gold atoms by iridium.