The efficient separation of CO2 from air remains
an
important and challenging goal for direct air capture (DAC). Herein,
iron-containing 13X zeolite (Fe@13X) with an efficient separation
of CO2 from the air was synthesized via a simple one-step
in situ crystallization method. The results demonstrate that Fe@13X
exhibited outstanding DAC performance (the CO2 capacity
of Fe@13X was 0.64 mmol/g, much higher than the 13X zeolite under
simulated air), which was attributed to the introduction of Fe atoms,
effectively narrowing the 13X micropore channel. Moreover, the DAC
adsorption performance of Fe@13X in the temperature range from 25
to 75 °C was explored by combined thermogravimetric analysis
and differential scanning calorimetry. The results revealed that low
temperatures were more favorable for the adsorption of CO2 with a high adsorption rate but less selectivity. Furthermore, Fe@13X
showed a 3 times higher CO2 production (0.003 kgCO2/kgads·h) and 3.6 times lower desorption energy (0.005
kW h/kgCO2
) than 13X zeolite in 400 ppm CO2 in N2. Finally, Fe@13X exhibited excellent cycle
stability in simulated air and maintained its initial CO2 uptake in 10 consecutive cycles, showing the broad application prospects
of materials in industrial adsorption and separation.
Solid amine adsorbents can efficiently adsorb CO2, but a significant problem is that amine groups are oxidized. In this research, tetraethylenepentamine‐impregnated MCM‐41 adsorbents (TEPA‐MCM‐41) were functionally modified with sulphur‐containing antioxidant 2‐mercaptobenzimidazole (described as antioxidant MB) and tns‐(2.4‐di‐tert‐butyl)‐phosphite (defined as antioxidant 168), respectively. The antioxidative degradation mechanism of 8% MB–50% TEPA‐MCM‐41 was analyzed by in situ diffuse reflectance infrared Fourier transform (in situ DRIFT) spectrum and high‐performance liquid chromatography/mass spectrometry (HPLC/mass). The CO2 adsorption capacity of 50% TEPA‐MCM‐41 was 4.30 mmol/g under 15% CO2/85% N2, but decreased to 1.38 mmol/g after oxidation at 100°C for 42 h under 95% N2/5% O2 certain condition. The CO2 capacity of 8% MB–50% TEPA‐MCM‐41 reduced from 3.90 to 2.86 mmol/g. After 30 adsorption cycles under 5% O2/15% CO2/80% N2, the capacity of 8% MB–50% TEPA‐MCM‐41 also only decreased by 16.8%, while 50% TEPA‐MCM‐41 decreased by 63.2%. The reason for the excellent antioxidant stability of 8% MB–50% TEPA‐MCM‐41 is that MB scavenged free radicals from amine oxidation and decomposed the hydroperoxides produced by free radical reactions. The hydroperoxides were decomposed into alcohols (non‐radical products), which were eventually oxidized to sulphonic compounds. The MB modification inhibited the oxidative degradation of solid amine adsorbents guided for the production of antioxidant‐efficient adsorbents.
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