Dehydrochlorination behavior of a chloride ion-intercalated hydrotalcite-like compound during thermal decomposition

We prepared a chloride ion-intercalated hydrotalcite-like compound (Cl⁻-HT) in a co-precipitation reaction, and investigated its thermal properties using thermogravimetry-differential thermal analysis (TG–DTA) and simultaneous thermogravimetry-mass spectrometry (TG-MS). In addition, we examined the effects of temperature and atmosphere on the dehydrochlorination of Cl⁻-HT during thermal treatment. The thermal decomposition of the Cl⁻-HT was divided into three stages: the evaporation of surface adsorbed water and interlayer water in the Cl⁻-HT, the dehydroxylation of the brucite-like octahedral layers in the Cl⁻-HT, and the elimination of HCl from the Cl⁻-HT. H₂O was produced at four steps: the evaporation of surface adsorbed water and interlayer water in the first stage, two steps of H₂O production caused by the dehydroxylation of the parts of Cl⁻-HT with properties similar to Mg(OH)₂ and Al(OH)₃, respectively, in the second stage, and H₂O production due to the dehydroxylation of the part of Cl⁻-HT with properties similar to Al(OH)₃ in the third stage. HCl was produced at two steps: the dehydrochlorination of the parts of Cl⁻-HT with properties similar to AlOCl and Mg(OH)Cl, respectively, in the third stage. Hydrochloric acid was obtained from the Cl⁻-HT on thermal treatment. The degree of dehydrochlorination of the Cl⁻-HT increased with temperature. The degree was greater under water vapor than under nitrogen at all temperatures, indicating that water vapor promoted the dehydrochlorination of Cl⁻-HT. However, the concentration of hydrochloric acid obtained under water vapor was lower than that under nitrogen.