High CO2 Storage Capacity in Alkali-Promoted Hydrotalcite-Based Material: In Situ Detection of Reversible Formation of Magnesium Carbonate

Alkali-promoted hydrotalcite-based materials showed very high CO2 storage capacity, exceeding 15 mmolg(-1) when the carbonation reaction was carried out at relatively high temperature (300-500 degrees C) and high partial pressure of steam and CO2. In situ XRD experiments have allowed correlation of high CO2 capacity to the transformation of magnesium oxide centres into magnesium carbonate in alkali-promoted hydrotalcite-based material. Moreover, it has been clearly shown that crystalline magnesium carbonate may be reversibly formed at temperatures above 300 degrees C in the presence of sufficient partial pressure of steam in the gas phase, conditions that are prevalent in pre-combustion CO2 capture. The role of steam appears to be of utmost importance for the formation of the bulk carbonate phase and for its reversibility. It is proposed that a high partial pressure of steam keeps the magnesium oxide periclase phase sufficiently hydroxylated to allow magnesium carbonate formation if a relatively high partial pressure CO2 is present in the gas phase.