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Issue 11, 1998
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Thermal evolution of cobalt hydroxides: a comparative study of their various structural phases

Abstract

Through an atmosphere-controlled method, a new phase of hydrotalcite-like Co hydroxide with mixed valent states has been synthesised, along with preparations of known α and β phases. Structural and thermal behaviours of all the Co hydroxides have been compared. Three major stages of decomposition are found: (i) 149-164°C for dehydration of interlayer water, (ii) 185-197°C and (iii) 219-222°C for dehydroxylation of hydrotalcite- and brucite-like phases, respectively. Intercalated nitrate anions in hydrotalcite-like phases decompose largely during stage (ii). The oxide Co 3 O 4 starts to form at temperatures as low as 165°C especially for hydrotalcite-like phases. An intermediate compound, HCoO 2 , which is formed thermally, decomposes at 258-270°C. The Co 3 O 4 oxide converts into CoO at 842-858 and 935-948°C respectively in nitrogen and air, which is much lower than the previously reported range of 1000-1200°C. Surface areas of calcined samples are found to be proportional to the intercalated anion content. The catalytic activity of the resultant Co 3 O 4 oxides with nitrous oxide is 7.2-8.2 mmol N 2 O g –1 h –1 at 375°C, which is comparable to some reported active catalyst systems.

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Article type: Paper
DOI: 10.1039/A804767G
Citation: J. Mater. Chem., 1998,8, 2499-2506
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    Thermal evolution of cobalt hydroxides: a comparative study of their various structural phases

    Z. P. Xu and H. C. Zeng, J. Mater. Chem., 1998, 8, 2499
    DOI: 10.1039/A804767G

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