Synthesis of hydrotalcite-like precursor compounds MgCo(II)Co(III)-HTlcs

Abstract

Precursor compounds of MgCo(II)Co(III)-HTlcs for Mg-Co oxide catalysts have been synthesized by coprecipitation in an ammoniacal solution and hydrothermal treatments under various O2/N2 atmospheres. Using elemental analysis (EA) and redox titration, it is found that about 23% of original Co2+ are oxidized to Co3+, resulting in formation of hydrotalcite-like (HTl) structure. The anion (NO3 -) intercalation increases with the rise in O2 partial pressure. X-ray diffraction pattern shows a conversion from brucite-like to HTl structures with increase of O2 partial pressure. It is found that thermal stability of the HTl-compounds is proportional to the Mg content. Higher specific surface areas are observed for decomposed products with low Co/Mg ratio. A trace amount of Co3O4 is also detected by FTIR for samples synthesized under high O2 partial pressures, which can be attributed to a deeper oxidation of Co2+.