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

Abstract

Alkali-promoted hydrotalcite-based materials showed very high CO₂ storage capacity, exceeding 15 mmol g⁻¹ when the carbonation reaction was carried out at relatively high temperature (300–500 °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 °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.