Gold Stabilized with Iridium on Ceria–Niobia Catalyst: Activity and Stability for CO Oxidation

Abstract

Monometallic gold and iridium, and bimetallic gold–iridium on ceria–niobia (Nb2O5–CeO2) catalysts were synthesized by deposition–precipitation with urea. Ceria–niobia support, synthesized by co-precipitation, presented a higher reducibility and a higher surface acidity as a consequence of the deposition of niobia on the ceria surface. The Au–Ir/CeNb showed an enhanced activity and stability during the carbon monoxide oxidation reaction as compared with the monometallic catalysts. These catalysts were thoroughly characterized chemical and structurally. High-resolution electron microscopy, UV–Vis spectroscopy and CO adsorption showed evidences of iridium-gold closeness. In situ infrared spectroscopy in the diffuse reflectance (DRIFT) mode was used to investigate the reactivity of the active sites. A lower coverage of carbonate species was observed under reaction as a result of the presence of niobia in the catalyst formulation. Concentration-modulation excitation spectroscopy (c-MES) allowed a selective identification of intermediates and ‘spectator’ species. New adsorption sites for CO were identified and correlated with the high activity and stability of the bimetallic catalyst.