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Despite the great attraction of using potassium promoted magnesium-aluminum layered double oxides (K-LDOs) as elevated temperature CO₂ adsorbents, the understanding of CO₂ adsorption mechanism of K-LDOs is still confusing and controversial due to the complexity of adsorbent compositions. In this work, in situ techniques were adopted to verify the synergistic mechanism of K₂CO₃ doping (0–40 wt%) and Mg/Al mole ratio (0.55, 2.17, and 2.98) on the CO₂ capture of K-LDOs. Before K₂CO₃ doping, the commercially available MG63 ([Mg_0.69Al_0.31(OH)₂](CO₃)_0.16·zH₂O) exhibited the highest working CO₂ capacity of 0.320 mmol/g at 400 °C and 1 atm. After doping with 20 wt% K₂CO₃, K₂₀-MG70 (Mg/Al ratio: 2.98) gave highest CO₂ capacity of 0.722 mmol/g. At low CO₂ partial pressures, however, K₂₀-MG30 (Mg/Al ratio: 0.55) with the lowest Mg/Al ratio owned the best capture performance. Results …