CoOx–FeOx composite oxide prepared by hydrothermal method as a highly active catalyst for low-temperature CO oxidation

• Published in: Journal of the Ceramic Society of Japan 2017/03/01, Vol.125(3), pp.135-140
• Main Authors: HANEDA, Masaaki, KAWAGUCHI, Yusuke, TOWATA, Atsuya
• Format: Article
• Language: English
• Subjects: CO oxidation; CoOx–FeOx composite oxides; FT-IR; H2-TPR; NO adsorption
• ISSN: 1882-0743; 1348-6535
• DOI: 10.2109/jcersj2.16219

A series of CoOx–FeOx composite oxides with different Co content was prepared using the hydrothermal method. Low-temperature activity of CoOx–FeOx composite oxides for CO oxidation was significantly improved by the addition of 50 atm % CoOx into FeOx. Further increase in Co content up to 70 atm % caused a decrease in low-temperature activity. Structural characterizations by X-ray diffraction, transmission electron microscope and Fourier transform infrared (FT-IR) revealed that Co species, which were not substituted with Fe sites to form CoFe2O4, are highly dispersed on the surface of CoFe2O4 particles with a perimeter interface for the samples with 50 atm % CoOx. The surface valence state of CoOx–FeOx composite oxides was found to be different by FT-IR spectroscopy following NO adsorption. CoOx–FeOx with 50 atm % CoOx includes a relatively large amount of quasi-tetrahedrally coordinated Co2+ sites on the surface, whereas that with 10 atm % CoOx consists of Fe2+ sites on the surface. Temperature-programmed reduction by H2 measurements suggested that CoOx–FeOx with 50 atm % CoOx possesses the largest amount of active oxygen species, which can be reduced by H2 in the lower temperature region. The surface oxygen species of which the formation is related to the presence of quasi-tetrahedrally coordinated Co2+ sites was concluded to participate in CO oxidation reaction on CoOx–FeOx composite oxides.