Thermal decomposition kinetics of MgAl layered double hydroxides

Structural, thermal profiles and kinetic behavior of two different sol–gel samples of MgAl layered double hydroxides (LDHs) were studied. In situ FT-IR study was used to follow the chemical composition changes, and thermal evolution of specific chemical species in each stage was monitored with a dynamic sampling mass spectrometer (TPD-MS analysis). The identified gas products were mainly OH, H2O, CO2, and organic species, mainly C2H5, originated from the alkoxy groups. The thermal evolution of intercalated compounds occurred in at least four steps related to dehydration, dehydroxylation of layers, interlayer anion decomposition, shrinkage and collapse of the layered structure, and finally crystallization of spinel MgAl2O4. Kinetic analysis in terms of activation energy (Ea), suggest that decomposition mechanism is a complex process that involves decomposition of several species and phase transformations.