Remarkable effects of hydroxyl species on low-temperature CO (preferential) oxidation over Ir/Fe(OH)x catalyst

• The Fe(OH)x promoted the formation of OH species during PROX process.
• The OH species came from reaction between O(ad) on Fe2+ sites and H(ad) on Ir sites.
• The OH species reacted with CO to produce CO2.
• The reaction between OH species and CO was prior to that between O(ad) and CO.

Fe(OH)x-supported noble metal catalysts exhibited good performance in low-temperature CO oxidation or CO preferential oxidation (PROX), which usually resulted from the high reducibility of Fe(OH)x. However, we found here that the use of Fe(OH)x promoted the formation of OH species during PROX over Ir/Fe(OH)x catalysts, which not only greatly lowered the temperature for 100% CO conversion, even to room temperature, but also improved the stability. These OH species originated from the reaction between the adsorbed O on Fe2+ sites and the adsorbed H on Ir sites. They changed the reaction route for the oxidation of CO through adsorbed CO and OH with lower activation energy (Ea: ∼5.2 kJ/mol) rather than through adsorbed CO and O (Ea: ∼15.4 kJ/mol). With further time-resolved mass spectroscopy and diffuse reflectance infrared spectroscopy, the OH species, prior to the adsorbed O, were proved to react with CO directly.

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