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: similar to 5.2 kJ/mol) rather than through adsorbed CO and O (Ea: similar to 15.4 kJ/mol). With further time-resolved mass spectroscopy and diffuse reflectance infrared spectroscopy, the OH species, prior to the adsorbed 0, were proved to react with CO directly. (C) 2014 Elsevier Inc. All rights reserved.