Inorganic carbonate composites as potential high temperature CO 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 g) 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 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 uptake at 650 °C (0.586 g g) to CaO sorbents obtained from pure HPACC (0.658 g g) and the commercial CaCO (0.562 g g). Over 23 adsorption-desorption cycles CMOs also showed a lower CO uptake capacity loss (35.7%) than CaO from HPACC (51.3%) and commercial CaCO (79.7%). Al was introduced to CMO by the addition of Al(NO) in the synthesis of CMC-3 to give ACMO after calcination. The presence of ∼19 mol% of Al(NO) 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 uptake. After 100 cycles, ACMO-4 still had a CO uptake of 0.219 g g. Scanning electron microscope images clearly showed that the presence of Mg and Al in CMO hindered the sintering of CaCO at high temperatures and therefore, enhanced the cycle stability of the CMO sorbents. We tested the CO 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 sorbents for various applications.