Al₂O₃/MgO-doped, CaO-based adsorbents for CO₂ capture: A performance study

Area of Science:

• Materials Science
• Chemical Engineering
• Environmental Science

Background:

• Calcium oxide (CaO) is crucial for CO2 capture in calcium looping processes.
• Sintering and structural degradation limit the cyclic stability and efficiency of CaO-based sorbents.
• Optimizing CaO sorbent performance requires careful consideration of precursor selection and doping strategies.

Purpose of the Study:

• To investigate the effect of different calcium precursors on CO2 adsorption performance.
• To evaluate the impact of Al2O3 and MgO doping on the capacity, kinetics, and cyclic stability of CaO sorbents.
• To develop a strategy for decoupling adsorption kinetics and cyclic stability in CaO-based CO2 adsorbents.

Main Methods:

• Direct calcination of four calcium precursors: calcium oxalate, calcium carbonate, calcium d-gluconate monohydrate, and commercial calcium carbonate.
• Systematic comparison of CO2 adsorption performance, including capacity, kinetics, and cyclic stability over multiple adsorption-desorption cycles.
• Characterization of sorbent structures using techniques to confirm structural evolution and understand the role of dopants.

Main Results:

• Calcium oxalate precursor (CaO-1) showed high initial CO2 adsorption (0.63 g/g) but poor cyclic stability (38% loss after 10 cycles) due to sintering.
• Al2O3 doping (CaO-Al2O3, 95/5) enhanced capacity (0.65 g/g) and kinetics (0.23 g/g·min-1) but still exhibited degradation (33.8% after 20 cycles).
• MgO doping (CaO-MgO, 85/15) provided exceptional cyclic stability, retaining 93% capacity over 10 cycles, attributed to enhanced sintering resistance.

Conclusions:

• Precursor engineering and dopant selection are critical for optimizing the trade-off between CO2 adsorption kinetics and cyclic stability.
• Al2O3 doping stabilizes pore networks, while MgO doping preserves framework integrity, mitigating sintering.
• A dual-dopant approach with optimal CaO-Al2O3 (95/5) and CaO-MgO (85/15) compositions offers a promising strategy for cost-effective, durable CO2 adsorbents for calcium looping.