Catalytic performance of a Bi2O3-Fe2O3 system in soot combustion

Bi2O3-Fe2O3 system catalysts were synthesized by a hydrothermal method in different ratios. Six materials were synthesized: Fe2O3, Bi2O3, Bi2O3/Fe2O3, BiFeO3, Bi2Fe4O9 and Bi25FeO40. The resulting catalysts were characterized by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), scanning electron microscopy (SEM), H-2-temperature-programmed reduction (TPR), and O-2-temperature-programmed desorption (TPD) measurements, and X-ray photoelectron (XPS) and Raman spectroscopies, in order to investigate their physical-chemical properties and to detect soot combustion through temperature-programmed experiments. XPS and O-2-TPD measurements show that composite catalysts have higher amounts of active oxygen than pure catalysts. The ratio of active oxygen is the largest in the Bi0.2Fe1.8 catalyst. All of the composite catalysts show superior low temperature catalytic activity than single Bi2O3 or Fe2O3 catalysts, and the Bi0.2Fe1.8 catalyst shows a minimum T-90 of 422 degrees C with the best catalytic properties, because Bi2O3 is able to increase the formation of oxygen vacancies by accelerating the transport rate of the active oxygen species (O-2(-)) for its high mobility and reactivity at the Bi-Fe interface layer. The mechanism of the Bi0.2Fe1.8 catalyst in the catalytic oxidation of soot is discussed.