An alumina phase induced composite transition shuttle to stabilize carbon capture cycles

Limiting global warming to 1.5-2 °C requires a 50-90% reduction in CO₂ emissions in 2050, depending on different scenarios, and carbon capture, utilization, and storage is a promising technology that can help reach this objective. Calcium oxide (CaO) carbon capture is an appealing choice because of its affordability, large potential capacity, and ability to withstand the high temperatures of flue gases. However, the structural instability and capacity fading challenge its large-scale industrial applications. Here, we design a reversible reaction shuttle in CaO-based sorbents to improve the structure stability by changing the initial alumina phases. Diverse alumina phases (x-Al₂O₃) are first synthesized and utilized as the aluminum source for creating CaO@x-Al₂O₃ composites. As expected, the CaO@δ-Al₂O₃ composite demonstrates a carbon capture capacity of 0.43 g-CO₂/g-sorbent after 50 cycles, with an impressive capacity retention of 82.7%. Combined characterizations and calculations reveal that this stability improvement is attributed to a transition shuttle between Ca₃Al₂O₆ and Ca₅Al₆O₁₄, which can effectively restrain the complete decompositions of those structure-stabilized intermediate phases. An economic assessment further identifies the significance of heat transfer efficiency improvement upon cycles, and control of capital/operation cost, energy price and carbon tax for a future cost-effective commercialization of current strategy.