High CO(2) 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 CO(2) 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 CO(2). In situ XRD experiments have allowed correlation of high CO(2) 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 CO(2) 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 CO(2) is present in the gas phase.

The crucial role of the K+-aluminium oxide interaction in K+-promoted alumina- and hydrotalcite-based materials for CO2 sorption at high temperatures.

CO(2)-free hydrogen can be produced from coal gasification power plants by pre-combustion decarbonisation and carbon dioxide capture. Potassium carbonate promoted hydrotalcite-based and alumina-based materials are cheap and excellent materials for high-temperature (300-500 degrees C) adsorption of CO(2), and particularly promising in the sorption-enhanced water gas shift (SEWGS) reaction. Alkaline promotion significantly improves CO(2) reversible sorption capacity at 300-500 degrees C for both materials. Hydrotalcites and promoted hydrotalcites, promoted magnesium oxide and promoted gamma-alumina were investigated by in situ analytical methods (IR spectroscopy, sorption experiments, X-ray diffraction) to identify structural and surface rearrangements. All experimental results show that potassium ions actually strongly interact with aluminium oxide centres in the aluminium-containing materials. This study unambiguously shows that potassium promotion of aluminium oxide centres in hydrotalcite generates basic sites which reversibly adsorb CO(2) at 400 degrees C.