The effect of preparation method on the activities of Pd–Fe–Ox/Al2O3 catalysts for CO oxidation

The Pd–Fe–Ox/Al2O3 catalysts were prepared by co-impregnation (co-Pd–Fe–Ox/Al2O3) and sol–gel method (sol–gel–Pd–Fe–Ox/Al2O3) and characterized by N2 adsorption–desorption, X-ray diffraction (XRD), H2-temperature programmed reduction (H2-TPR), and X-ray photoelectron spectroscopy (XPS). The CO catalytic oxidation was investigated over Pd–Fe–Ox/Al2O3 catalysts prepared by different methods. The 100% conversion temperature (T100) over pre-reduced co-Pd–Fe–Ox/Al2O3 (co-Pd–Fe–Ox/Al2O3–R) and pre-reduced sol–gel–Pd–Fe–Ox/Al2O3 (sol–gel–Pd–Fe–Ox/Al2O3–R) is 90 and 25 °C when fed with the reaction mixture containing 1 vol.% CO and a balance of air, respectively. XRD results indicate that the sol–gel method is favorable for the high dispersion of PdO particles compared with co-impregnation method. H2-TPR results suggest that the interaction between Pd and Fe is existent over both sol–gel–Pd–Fe–Ox/Al2O3 and co-Pd–Fe–Ox/Al2O3 catalysts, while the interaction in former catalyst is stronger than that in the latter. The XPS results show that the Pd species on the surface of both sol–gel–Pd–Fe–Ox/Al2O3–R and co-Pd–Fe–Ox/Al2O3–R catalysts are the mixture of oxide and metal state, leading to the high activity for CO oxidation. Furthermore, the different Pd2+/Pd0 ratio may be the reason for the different activity between sol–gel–Pd–Fe–Ox/Al2O3–R and reduced co-Pd–Fe–Ox/Al2O3–R catalysts.