Abstract: The compound Mg2+-Al3+-(Fe(CN)6)4−, with a structure similar to hydrotalcite Mg6Al2(OH)16CO3·4H2O, is prepared by a coprecipitation method. Chemical, thermal, and X-ray analysis of the compound lead to the formula: (Mg0.741Al0.259(OH)2)((FeII(CN)6)0.067(CO3)0.002(H2O)1.05)
The compound is dehydrated at 100° to 250°C and the adsorption of N2, O2, CO2, and H2 on it is measured at −196°C to room temperature by the volumetric method. The water is removed reversibly from 100° to 200°C and the interstices after dehyration act as sites of adsorption. When dehydration is carried out at 150°C the adsorptive activity reaches a maximum. Adsorption isotherms of N2 and O2 at −196°C and of CO2 at room temperature are of the Langmuir type, and the saturated amounts of N2, O2, and CO2 adsorbed are 96.3, 65.2, and 91.8 ml (STP)/g, respectively.
Adsorption isotherms of N2 and O2 at room temperature are of the Henry type. The amount of O2 adsorbed is about 67% of that of N2. The isosteric heats of adsorption at room temperature of N2, O2, and CO2 are 5.1, 4.8, and 11.0 kcal/mol, respectively. A dehydrated product of a Mg2+-Al2+-CO32− compound does not permit adsorption of CO2 at room temperature, but permits the adsorption of H2O. Hence, it has a molecular sieve effect. No adsorption of H2 is observed in any of the compounds tested.