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Solid amine adsorbents are among the most promising CO 2 adsorption technologies for biogas upgrading due to their high selectivity toward CO 2 , low energy consumption, and easy regeneration. However, in most cases, these adsorbents undergo severe chemical inactivation due to urea formation when regenerated under a realistic CO 2 atmosphere. Herein, we demonstrated a facile and efficient synthesis route, involving the synthesis of nano-Al 2 O 3 support derived from coal fly ash with a CO 2 flow as the precipitant and the preparation of polyethylenimine (PEI)-impregnated Al 2 O 3 -supported adsorbent. The optimal 55%PEI@2%Al 2 O 3 adsorbent showed a high CO 2 uptake of 139 mg•g −1 owing to the superior pore structure of synthesized nano-Al 2 O 3 support and exhibited stable cyclic stability with a mere 0.29% decay per cycle even under the realistic regenerated CO 2 atmosphere. The stabilizing mechanism of PEI@nano-Al 2 O 3 adsorbent was systematically demonstrated, namely, the cross-linking reaction between the amidogen of a PEI molecule and nano-Al 2 O 3 support, owing to the abundant Lewis acid sites of nano-Al 2 O 3 . This cross-linking process promoted the conversion of primary amines into secondary amines in the PEI molecule and thus significantly enhanced the cyclic stability of PEI@nano-Al 2 O 3 adsorbents by markedly inhibiting the formation of urea compounds. Therefore, this facile and efficient strategy for PEI@nano-Al 2 O 3 adsorbents with anti-urea properties, which can avoid active amine content dilution from PEI chemical modification, is promising for practical biogas upgrading and various CO 2 separation processes.

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