A study by in situ techniques of the thermal evolution of the structure of a Mg–Al–CO 3 layered double hydroxide

Abstract

Several in situ techniques have been used to investigate the thermal evolution of the structure of a Mg–Al–CO 3 layered double hydroxide (LDH) under an inert atmosphere. Based on the results of the study, a model is proposed to describe the structural evolution of the Mg–Al–CO 3 LDH. According to this model as the temperature is increased, loosely held interlayer water is lost in the temperature range of 70–190°C, but the LDH structure still remains intact. The OH − group, likely in a Al–(OH)–Mg configuration, begins to disappear at 190°C, and is completely lost at 280°C; a gradual transformation of the LDH structure begins in the same range of temperatures. The OH − group, likely in a Mg–(OH)–Mg configuration, begins to disappear at 280°C and is completely lost at 405°C; a gradual degradation of the LDH structure is observed in the same range. Although some CO 3 2− loss is observed at lower temperatures, its substantial loss begins at 410°C, and is completed at 580°C. At these temperatures the material becomes an amorphous metastable, mixed solid oxide solution.