Catalytic performance of a Bi2O3–Fe2O3 system in soot combustion

Abstract

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), H₂-temperature-programmed reduction (TPR), and O₂-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 O₂-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 Bi_0.2Fe_1.8 catalyst. All of the composite catalysts show superior low temperature catalytic activity than single Bi₂O₃ or Fe₂O₃ catalysts, and the Bi_0.2Fe_1.8 catalyst shows a minimum T₉₀ of 422 °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 (O₂⁻) for its high mobility and reactivity at the Bi–Fe interface layer. The mechanism of the Bi_0.2Fe_1.8 catalyst in the catalytic oxidation of soot is discussed.