Reaction mechanism of Ca2Fe2O5 oxygen carrier with CO in chemical looping hydrogen production

Abstract

The CO adsorption behavior, CO oxidation and oxygen anion diffusion of Ca2Fe2O5(010) surface were systematically investigated to deeply understand the reaction mechanism of Ca2Fe2O5 oxygen carrier with CO based on density functional theory (DFT) calculations. The results indicate that the activity of CO adsorption on four terminations of Ca2Fe2O5(010) surface follows the order: FeO2- terminated > FeO-terminated > CaO-terminated > OCa-terminated. Four reaction pathways for CO oxidation were proposed. It was found that CO oxidation reaction is very easy to proceed, and that both types of surface oxygen (O1 and O2) could exhibit high activity. The oxygen diffusion in Ca2Fe2O5 is inherently a high-temperature process. In addition, the energy barrier of oxygen diffusion is much higher than that of CO oxidation, implying that oxygen diffusion is the rate-limiting step for the entire reaction between Ca2Fe2O5 oxygen carrier and CO. The superior reactivity of Ca2Fe2O5 oxygen carrier is attributed to its excellent surface oxygen activity and good oxygen diffusion ability.