Study on MNO₃/NO₂ (M = Li, Na, and K)/MgO Composites for Intermediate-Temperature CO₂ Capture

Molten salt [MNO 3 /NO 2 (M = Li, Na, and K)]-promoted MgO composite-type CO 2 adsorbents with high capacity and cycling stability are fabricated by controlled hydrolysis along with an incipient impregnation approach. The remarkable results of molten salts on the CO 2 capture performance of MgO adsorbents and the CO 2 capture capacities with different loadings and calcination and adsorption temperatures were comprehensively investigated. Notably, optimized NaNO 3 -promoted MgO exhibited the highest CO 2 capture capacity of 17.0 mmol g –1 at 350 °C and maintained excellent regenerability through multiple cycles. The initial CO 2 uptakes of MNO 3 /NO 2 (M = Li, Na, and K)/MgO composites follow the order of NaNO 3 (17.0 mmol g –1 ) > LiNO 3 (14.1 mmol g –1 ) > NaNO 2 (12.5 mmol g –1 ) > KNO 2 (9.3 mmol g –1 ) > KNO 3 (5.0 mmol g –1 ). Furthermore, NaNO 3 and KNO 3 with good chemical stability are the effective constituents for the NaNO 3 system and KNO 3 /KNO 2 -promoted system, respectively, and preserved their original form after the interaction with CO 2 . The NaNO 2 system consists of NaNO 3 and Na 2 CO 3 to form double carbonates Na 2 Mg(CO 3 ) 2 after CO 2 adsorption. The morphology and structure of the MgO skeleton and the introduction of promoters are essential factors for intermediate-temperature CO 2 capture.