Synthesis of Highly Effective CeO x –MnO y –BaO Catalysts for Direct NO Decomposition
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Ce–Mn mixed oxides with a Mn/(Ce + Mn) molar ratio of 0.25 were prepared by solvothermal (ST-1) and co-precipitation (CP) methods, and Ba was loaded on the Ce–Mn oxides. In addition, CeO2–MnO x –BaO catalysts with various compositions were directly prepared by the solvothermal (ST-2) method. The NO decomposition activities of these catalysts were examined. Among the catalysts examined, the ST-2 catalyst having a nominal composition of Ce0.8Mn0.15Ba0.05O x exhibited the highest activity; 77% NO conversion to N2 was attained at 800 °C. These catalysts were characterized by X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The Raman and XPS results indicate that the CP catalyst had larger amounts of the BaMnO3-δ and/or Mn3O4 phases. The ST-1 and ST-2 catalysts had highly dispersed Ba species on the surface. The ST-2 catalyst had Mn species with the lowest binding energy of Mn 2p and also had a high population of oxygen vacancies in the ceria lattice, suggesting that Mn species with a low oxidation state contributes to the formation of oxygen vacancies, which play an important role in this reaction.
KeywordsCeria Manganese oxide Barium Mixed oxide catalysts Direct NO decomposition Solvothermal method
We are grateful to Prof. Takeshi Abe of Kyoto University for his help in Raman spectra measurements and Dr. Seiichiro Imamura and Dr. Hiroyoshi Kanai of Kyoto University for their invaluable advice.
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