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.