Review on the Theoretical Understanding of Oxygen Carrier Development for Chemical-Looping Technologies

Chemical-looping combustion (CLC) is a novel and promising low-cost CO2 separation technology. The development of an oxygen carrier with high performance is the key to the successful application of CLC. Since it is still challenging for experimental measurements to acquire detailed information on the atomic mechanisms between the oxygen carrier and fuels or impurities. Alternatively, theoretical methods based on density functional theory (DFT) have become a powerful tool to study the electronic and structural properties of materials, as well as to clearly reveal the underlying microscopic mechanisms, which is helpful to rationally design high-performance oxygen carriers. Hence, the application of DFT in understanding the mechanisms for oxygen carrier development during the chemical-looping process is reviewed. The reactivity and detailed reaction mechanism of oxygen carriers are summarized, and the interaction between various components and the synergy in oxygen carriers are revealed. Particularly, the influences of foreign components (e.g., inert supports and dopants), adsorbate interaction, and surface structure on the reactivity of oxygen carriers are comprehensively discussed. Most of the examples discussed are mainly concerned with the reaction characteristics on the oxygen carrier surfaces. DFT calculations performed to understand and predict variations in reactivity from one oxygen carrier to another are emphasized. Moreover, the DFT method can also be employed to evaluate and screen oxygen carriers with appropriate properties including resistance to sintering, selectivity for production, and so forth. Finally, tentative future works on essential challenges and possible opportunities of understanding chemical-looping technology based on DFT calculations are preliminarily provided.