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Abstract

An Ir-in-ceria catalyst has been developed, in which most of the iridium particles are embedded in the ceria matrix through the redox reaction between Ce³⁺ and Ir⁴⁺, which occurred during co-precipitation (CP). This Ir-CP catalyst exhibited high activity for preferential CO oxidation under excess hydrogen conditions, and the selectivity to CO₂ remained nearly constant, at around 70%, with increasing reaction temperature. Temperature-programmed reduction and in situ diffuse reflectance infrared spectroscopy techniques were used to explore the structure of the Ir-CP catalyst and to correlate it with the catalytic performance. It was found that the CeO₂ support was activated by iridium and formed on the surface the active sites for CO oxidation. Due to the absence of extensively exposed Ir species on the Ir-CP catalyst, H₂ oxidation occurring on the Ir species and the ceria support at high temperatures was significantly suppressed, thus keeping the selectivity to CO₂ at a high level.