The effect of preparation method on the activities of Pd-Fe-Ox/Al _2O_3 catalysts for CO oxidation

摘要

The Pd-Fe-Ox/Al_2O_3 catalysts were prepared by co-impregnation (co-Pd-Fe-Ox/Al_2O_3) and sol-gel method (sol-gel-Pd-Fe-Ox/Al_2O_3) and characterized by N _2 adsorption-desorption, X-ray diffraction (XRD), H _2-temperature programmed reduction (H_2-TPR), and X-ray photoelectron spectroscopy (XPS). The CO catalytic oxidation was investigated over Pd-Fe-Ox/Al_2O_3 catalysts prepared by different methods. The 100% conversion temperature (T 100) over pre-reduced co-Pd-Fe-Ox/Al_2O_3 (co-Pd-Fe-Ox/Al_2O _3-R) and pre-reduced sol-gel-Pd-Fe-Ox/Al_2O_3 (sol-gel-Pd-Fe-Ox/Al_2O_3-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. H _2-TPR results suggest that the interaction between Pd and Fe is existent over both sol-gel-Pd-Fe-Ox/Al_2O_3 and co-Pd-Fe-Ox/Al_2O_3 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/Al_2O _3-R and co-Pd-Fe-Ox/Al_2O_3-R catalysts are the mixture of oxide and metal state, leading to the high activity for CO oxidation. Furthermore, the different Pd~(2+)/Pd~0 ratio may be the reason for the different activity between sol-gel-Pd-Fe-Ox/Al_2O _3-R and reduced co-Pd-Fe-Ox/Al_2O_3-R catalysts.