Design of a novel bifunctional catalyst IrFe/Al2O3 for preferential CO oxidation

In this study, a novel bifunctional catalyst IrFe/Al₂O₃, which is very active and selective for preferential oxidation of CO under H₂-rich atmosphere, has been developed. When the molar ratio of Fe/Ir was 5/1, the IrFe/Al₂O₃ catalyst performed best, with CO conversion of 68% and oxygen selectivity towards CO₂ formation of 86.8% attained at 100 °C. It has also been found that the impregnation sequence of Ir and Fe species on the Al₂O₃ support had a remarkable effect on the catalytic performance; the activity decreased following the order of IrFe/Al₂O₃ > co-IrFe/Al₂O₃ > FeIr/Al₂O₃. The three catalysts were characterized by XRD, H₂-TPR, FT-IR and microcalorimetry. The results demonstrated that when Ir was supported on the pre-formed Fe/Al₂O₃, the resulting structure (IrFe/Al₂O₃) allowed more metallic Ir sites exposed on the surface and accessible for CO adsorption, while did not interfere with the O₂ activation on the FeO_x species. Thus, a bifunctional catalytic mechanism has been proposed where CO adsorbed on Ir sites and O₂ adsorbed on FeO_x sites; the reaction may take place at the interface of Ir and FeO_x or via a spill-over process.