Zp. Xu et Hc. Zeng, THERMAL REVOLUTION OF COBALT HYDROXIDES - A COMPARATIVE-STUDY OF THEIR VARIOUS STRUCTURAL PHASES, Journal of materials chemistry (Print), 8(11), 1998, pp. 2499-2506
Through an atmosphere-controlled method, a new phase of hydrotalcite-l
ike Co hydroxide with mixed valent states has been synthesised, along
with preparations of known alpha and beta phases. Structural and therm
al behaviours of all the Co hydroxides have been compared. Three major
stages of decomposition are found: (i) 149-164 degrees C for dehydrat
ion of interlayer water, (ii) 185-197 degrees C and (iii) 219-222 degr
ees C for dehydroxylation of hydrotalcite- and brucite-like phases, re
spectively. Intercalated nitrate anions in hydrotalcite-like phases de
compose largely during stage (ii). The oxide Co3O4 starts to form at t
emperatures as low as 165 degrees C especially for hydrotalcite-like p
hases. An intermediate compound, HCoO2, which is formed thermally, dec
omposes at 258-270 degrees C. The Co3O4 oxide converts into CoO at 842
-858 and 935-948 degrees C respectively in nitrogen and air, which is
much lower than the previously reported range of 1000-1200 degrees C.
Surface areas of calcined samples are found to be proportional to the
intercalated anion content. The catalytic activity of the resultant Co
3O4 oxides with nitrous oxide is 7.2-8.2 mmol N2O g(-1) h(-1) at 375 d
egrees C, which is comparable to some reported active catalyst systems
.