Synthesis and evaluation as CO_2 chemisorbent of the Li_5(Al_(1-x)Fe_x)O_4 solid solution materials: Effect of oxygen addition

Pentalithium aluminate (β-Li₅AlO₄) and the corresponding iron-containing solid solution (Li₅(Al_1−xFe_x)O₄) were synthetized by solid-state reaction. All the samples were characterized structural and microstructurally by X-ray diffraction, solid-state nuclear magnetic resonance, scanning electron microscopy, N₂ adsorption-desorption and temperature-programmed desorption of CO₂. Results showed that 30 mol% of iron can be incorporated into the β-Li₅AlO₄ crystalline structure at aluminum positions. Moreover, iron addition induced morphological and superficial reactivity variations. Li₅(Al_1−xFe_x)O₄ samples chemisorbed CO₂ between 200 and 700 °C, where the superficial chemisorption presented the highest enhancement, in comparison to β-Li₅AlO₄. Additionally, Li₅(Al_1−xFe_x)O₄ samples sintered at higher temperatures than β-Li₅AlO₄. Isothermal CO₂ chemisorption experiments of β-Li₅AlO₄ and Li₅(Al_1−xFe_x)O₄ were fitted to a first order reaction model, corroborating that iron enhances the CO₂ chemisorption, kinetically. When oxygen was added to the gas flow, CO₂ chemisorption process was mainly enhanced between 400 and 600 °C for the Li₅(Al_0.8Fe_0.2)O₄ sample in comparison to β-Li₅AlO₄. Hence, Li₅(Al_1−xFe_x)O₄ solid solution presented an enhanced CO₂ chemisorption process, in the presence and absence of oxygen, in comparison to β-Li₅AlO₄.