A first-principles density functional theory study of the electronic structural and thermodynamic properties of M2ZrO3 and M2CO3 (M=Na, K) and their capabilities for CO2 capture

Alkali metal zirconates could be used as solid sorbents for CO2 capture. The structural, electronic, and phonon properties of Na2ZrO3, K2ZrO3, Na2CO3, and K2CO3 are investigated by combining the density functional theory with lattice phonon dynamics. The thermodynamics of CO2 absorption/desorption reactions of these two zirconates are analyzed. The calculated results show that their optimized structures are in a good agreement with experimental measurements. The calculated band gaps are 4.339 eV (indirect), 3.641 eV (direct), 3.935 eV (indirect), and 3.697 eV (direct) for Na2ZrO3, K2ZrO3, Na2CO3, and K2CO3, respectively. The calculated phonon dispersions and phonon density of states for M2ZrO3 and M2CO3 (M=K, Na, Li) revealed that from K to Na to Li, their frequency peaks are shifted to high frequencies due to the molecular weight decreased from K to Li. From the calculated reaction heats and relationships of free energy change versus temperatures and CO2 pressures of the M2ZrO3 (M K, Na, Li) reacting with CO2, we found that the performance of Na2ZrO3 capturing CO2 is similar to that of Li2ZrO3 and is better than that of K2ZrO3. Therefore, Na2ZrO3 and Li2ZrO3 are good candidates of high temperature CO2 sorbents and could be used for post-combustion CO2 capture technologies. [doi:10.1063/1.3683519]