Synthesis and CO₂ Adsorption Features of a Hydrotalcite-Like Compound of the Mg²⁺-Al³⁺-Fe(CN)₆⁴⁻ System with High Layer-Charge Density

Hydrotalcite-like compounds (HT) with 24%–48% Al 3+ -substitution have been synthesized in the Mg 2+ -Al 3+ -Fe(CN) 6 4- system. Conditioning of the synthesized and air-dried compound with K 4 Fe(CN) 6 4- solution at 80°C was essential to obtain the 80%–90% pure ionic Fe(CN) 6 4- form on an equivalent basis. A linear decrease in a o with an increase in the mole ratio of R = Al 3+ /(Mg 2+ + Al 3+ ) was extended to R = 0.48. The formation of highly Al 3+ -substituted HTs has been corroborated by the decrease in the hexagonal lattice constant a o down to 3.016 Å. The a o value was independent of the interlayer anions. The CO 2 adsorption profiles were dependent upon both the Al 3+ -substitution and the interlayer distance. The isosteric heat of CO 2 adsorption was 43.3 kJ mol -1 in the range of adsorption of 20 to 40 cm 3 g -1 at 298 K and 0.1 MPa.