PREPARATION AND THERMAL-STABILITY OF MANGANESE-CONTAINING HYDROTALCITE, [MG0.75MN(II)0.04MN(III)0.21(OH)2] (CO3)0.11.NH2O

A magnesium-manganese hydroxycarbonate with the hydrotalcite structure has been synthesized by coprecipitation from aqueous solutions of Mg2+ and Mn2+. According to temperature-programmed reduction data, 84% of the manganese is oxidized to Mn3+ during synthesis. Fourier-transform infrared spectroscopy, powder X-ray diffraction and transmission electron microscopy data support the hydrotalcite structure. Thermal decomposition in air at 390-degrees-C leads to an amorphous material with a simultaneous increase of the specific surface area. Further calcination at higher temperatures (670 and 1000-degrees-C) leads to crystallization of MgO and Mg2MnO4 spinel and to sintering. Reduction of the spinel takes place in two separate steps, probably through formation of intermediate Mn3O4 and finally MnO.