57Fe Mossbauer Spectroscopy of Ir-Fe Catalysts for Preferential CO Oxidation in H2

New insights on the interaction between Ir and Fe oxide are reported. Three Ir-Fe catalysts were prepared by different impregnation sequences of an Al2O3 support. Co-impregnation gave a better catalyst for the preferential CO oxidation in H-2 (PROX) reaction. Microcalorimetry data showed that the adsorption of CO and H-2 were different. Quasi in situ Mossbauer data of the three catalysts after reduction, reoxidation, and PROX reaction showed that a strong interaction between Ir and Fe affected the redox properties of the Ir-Fe catalysts. CO conversion was proportional to the concentration of the Fe2+(a) species, thus, Fe2+(a) was an active site in the PROX reaction. The impregnation sequence influenced the interaction between Ir and Fe and consequently, the amount of the active Fe2+(a) species. A strong Ir-Fe interaction stabilized the active Fe2+ sites for activating O-2.