Soot particulate (mainly carbon nano-particulate), as one of the main hazardous substances in diesel engine exhaust, has seriously adverse impact on environment and public health. Diesel particulate filter (DPF) has been proved to be the most reliable and economical after-treatment technology for soot emission control, However, the classical temperatures in diesel engine exhaust pipes (200-400 °C) cannot afford to spontaneous combustion of the deposited soot (above 600 °C). The usage of a high-performance catalyst coated on the wall of DPF (CDPF), which enable to catalyze soot oxidation to CO2 at relatively low temperatures. Co3O4 has been proved to behave excellent activity for oxidation reaction due to its strong redox ability. Bi2O3 shows high anion conductivity and reducibility, which could be used as dopant to improve the redox ability and O2- ions mobility of metal oxides. In the present work, Bi2O3-Co3O4 catalysts were prepared by sol-gel method and tested for soot oxidation by O2. The composite oxides showed excellent activity under both tight and loose contact when compared with individual Co3O4 or Bi2O3, and the maximum activity was obtained over catalyst with Bi/Co molar ratio of 0.2. The samples were characterized by means of XRD, N2 adsorption, FE-SEM, XPS, FT-IR, C-TPR and O2-TPD. It was found that Bi2O3 with low melting point deposited on Co3O4 surface could not only promote the contact state between soot and catalyst, but also produce more oxygen species with high mobility and reactivity at Bi-Co interface layer. Oxygen activation channel and reaction pathway were discussed based on the results of isothermal anaerobic titrations and 18O-isotopic tests, which confirmed that soot was more likely to react with lattice oxygen species rather than O2, especially at low temperatures. The high mobility of lattice oxygen species was attributed to a combination of the O2- conductivity of Bi2O3 and the accelerative formation of oxygen vacancies at Bi-Co interface. A feasible reaction mechanism over the binary catalysts for soot oxidation was proposed. The stability tests were also studied and the results indicated that Bi-modified Co3O4 showed prominent tolerance against thermal shock, H2O and SO2, thus being a promising active component for practical application.

Activity and stability of Co3O4-based catalysts for soot oxidation: The enhanced effect of Bi2O3 on activation and transfer of oxygen

254th National Meeting (2017)

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