Inorganic carbonate composites as potential high temperature CO 2 sorbents with enhanced cycle stability.

A calcium magnesium carbonate composite (CMC) material containing highly porous amorphous calcium carbonate (HPACC) and mesoporous magnesium carbonate (MMC) was synthesized. CMCs with varying HPACC : MMC mol ratios and high BET surface area (over 490 m 2 g -1 ) were produced. The CMCs retained the morphology shared by HPACC and MMC. All these materials were built up of aggregated nanometer-sized particles. We tested the CO 2 uptake properties of the synthesized materials. The CMCs were calcined at 850 °C to obtain the corresponding calcium magnesium oxide composites (CMOs) that contained CaO : MgO at different mol ratios. CMO with CaO : MgO = 3 : 1 (CMO-3) showed comparable CO 2 uptake at 650 °C (0.586 g g -1 ) to CaO sorbents obtained from pure HPACC (0.658 g g -1 ) and the commercial CaCO 3 (0.562 g g -1 ). Over 23 adsorption-desorption cycles CMOs also showed a lower CO 2 uptake capacity loss (35.7%) than CaO from HPACC (51.3%) and commercial CaCO 3 (79.7%). Al was introduced to CMO by the addition of Al(NO 3 ) 3 in the synthesis of CMC-3 to give ACMO after calcination. The presence of ∼19 mol% of Al(NO 3 ) 3 in ACMO-4 significantly enhanced its stability over 23 cycles (capacity loss of 5.2%) when compared with CMO-3 (calcined CMC-3) without adversely affecting the CO 2 uptake. After 100 cycles, ACMO-4 still had a CO 2 uptake of 0.219 g g -1 . Scanning electron microscope images clearly showed that the presence of Mg and Al in CMO hindered the sintering of CaCO 3 at high temperatures and therefore, enhanced the cycle stability of the CMO sorbents. We tested the CO 2 uptake properties of CMO and ACMO only under ideal laboratory testing environment, but our results indicated that these materials can be further optimized as good CO 2 sorbents for various applications.