CO 2 Chemisorption on Li 5 AlO 4 : Effects of Sodium and Potassium Carbonate Addition
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CO2 Chemisorption on Li5AlO4: Effects of Sodium and Potassium Carbonate Addition M. Teresa Flores-Martínez and Heriberto Pfeiffer Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México, Circuito Exterior s/n, Ciudad Universitaria, Del. Coyoacán, CP 04510, México D.F, México. ABSTRACT In this work, Na- and K-doped β-Li5AlO4 samples were synthesized, characterized and analyzed thermogravimetrically (dynamically and isothermally), under different CO2 conditions. Additionally, chemisorption/desorption cycles were performed for the best chemical compositions and thermal conditions determined. While the CO2 chemisorption of the Na- and K-doped β-Li5AlO4 samples was improved at high temperatures (450 -700 °C), the opposite effect was observed at lower temperatures as well as in the presence of water vapor. INTRODUCTION CO2 is the main anthropogenic greenhouse gas in the atmosphere. The large amount of CO2 present in it is the cause of global warming and climate change [1]. In order to mitigate this problem, the following alternatives have been proposed to reduce the amount of anthropogenic CO2 emissions: capture, storage and reuse of the emitted CO2 [2]. In this way, the development of technologies to capture and/or sequester CO2 is desirable. Over the last two decades, several materials have been proposed as potential CO2 captors [3], such as zeolites, activated carbons, hydrotalcites, supported amines and different alkaline and alkaline earth ceramics, among others, due to their favorable sorption behavior [2,3]. Recently, lithium-based ceramics and other alkali elements have aroused great interest due to their high CO2 absorption capacity at elevated temperatures. Among these ceramics, Li5AlO4 seems to be one of the best possible options as a CO2 captor because of its high theoretical CO2 chemisorption capacity (15.9 mmol/g). Additionally, Li5AlO4 is able to chemisorb CO2 over a wide temperature range (200-700 °C) [4]. Moreover, Li5AlO4 exhibits a high CO2 chemisorption capacity in a multicycle test, which is considerably higher in comparison with other lithium ceramics tested as CO2 captors [4]. However, after many cycles, Li5AlO4 exhibits a gradually reduced chemisorption capacity. On the other hand, Li5AlO4 is not able to capture CO2 at temperatures below 100 °C, under dry conditions; however, considerably higher capture efficiencies are observed in the presence of water vapor. This is due to hydration and consequent hydroxylation processes taking place in the material. This has been reported in the temperature range of 30-80 °C for D-Li5AlO4 [5]. The CO2 chemisorption process is considerably more efficient in Na2CO3- and K2CO3doped lithium ceramics than in the respective alkali-pure ceramics [6, 7]. This behavior is explained by the formation of eutectic mixtures, which contain lithium carbonate (formed during the CO2 chemisorption at high temperatures) and the previously added carbonate. At this temperature, a partial melting is produced at the surface of the particles, which favors dif
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