CaAlFe-mixed metal oxides prepared from an aluminum salt-cake and their evaluation as CO2 sorbents at moderate temperature

Potentially-CO2 adsorbing solids at moderate temperature have been prepared by calcination at 400 degrees C and 750 degrees C of CaAlFe hydrocalumites (a sort of Ca2+-layered double hydroxide), which had been prepared using a salt cake as aluminum source. The characterization of the obtained solids was carried out by powder X-ray diffraction, FT-infrared spectroscopy, thermal analysis, N2 adsorption-desorption isotherms at -196 degrees C and electron microscopy. After calcination, different crystalline phases were identified as a function of the amount of Fe3+ incorporated. Static sorption equilibrium experiments were performed at 300 degrees C and pCO2 = 0.3 bar. The CO2 sorption capacity was affected by the presence of different phases in the CaAlFe-mixed oxides (MMOs), being maximum when the amount of Fe3+ was 40 mol % of the trivalent positions. No differences in CO2 sorption capacities were observed between CaAlFe-MMOs-400 and CaAlFe-MMOs-750 (materials calcined respectively at 400 and 750 degrees C), suggesting that CO2 sorption capacity was not related to SBET. Experiments under dynamic conditions at 400 degrees C and pCO2 = 0.15 bar showed good behaviors for CaAl-400, CaAl0.60Fe0.40-400 and CaFe-400. In addition, CaAl0.60Fe0.40-400 was evaluated in several CO2 sorption-desorption cycles in the presence of water vapor, finding that the steam presence enhanced the CO2 capture.