Role of urea hydrolysis in the sol-gel synthesis of Ca₃Al₂O₆-modified CaO for ultra-stable CO₂ capture

초록

CaO-based sorbents are known for their high CO2 sorption capacity; however, they suffer from gradual deactivation during cyclic usage. To effectively enhance cyclic stability, this study introduced Ca3Al2O6 into CaO as a structural stabilizer via the urea-assisted citrate sol-gel method. Gradually controlling the pH through urea hydrolysis resulted in the formation of a more stable colloidal sol, leading to reduced particle size and the development of a porous structure. This enhancement improved CO2 mass transfer into the CaO particles and significantly boosted the CO2 sorption kinetics of the CaO-based sorbents. Additionally, urea caused the Ca3Al2O6 crystallites to primarily disperse mainly on the surface of the CaO particles, markedly improving cyclic stability even with a small amount of stabilizer. The Ca3Al2O6-modified CaO exhibited perfect cyclic stability without any loss of CO2 sorption uptake over 10 repeated cycles of sorption and regeneration at 700 degrees C, exhibiting an average working capacity of similar to 55.1 wt%; it is more interesting in that the developed sorbent can capture and release CO2 at identical temperature just by switching the gas atmosphere. Significant decrease in regeneration temperature is also attributed to enhanced CO2 mass transfer. Therefore, Ca3Al2O6-modified CaO, exhibiting fast CO2 sorption/regeneration kinetics and outstanding cyclic stability, could be beneficial for direct CO2 capture at high temperatures.

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