Effect of Chemical Composition and Crystal Phase of (Li,Na)FeO2 Ferrites on CO2 Capture Properties at High Temperatures

In this work, we present the synthesis of lithium- and sodium-based ferrites by nitrate decomposition, using low and short thermal treatments. X-ray diffraction and Rietveld refinement were used to identify three different crystal phases: cubic, rhombohedral, and orthorhombic. By means of thermogravimetric experiments under CO2 atmosphere, it was found that cubic-phase samples did not present an important CO2 capture from 30 to 900 degrees C. However, rhombohedral and orthorhombic phases showed large capture properties at the same temperature range. The rhombohedral phase displayed a maximum CO2 capture with 65% of expected capture (750 degrees C), while the orthorhombic phase showed 90% of the expected capture (700 degrees C). Additionally, the double exponential model, together with the Eyring model, were used to obtain rate constants and enthalpy of the activated states for CO2 capture. From these data, a correlation of each capture process with the crystal structure and chemical composition was carried out. Finally, structural parameters together with electronegativity and hardness in chemical bonding were used to explain capture properties among the studied compositions.