Selective Adsorption of CO2 on Zeolites NaK-ZK-4 with Si/Al of 1.8–2.8,ACS Omega

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Selective Adsorption of CO2 on Zeolites NaK-ZK-4 with Si/Al of 1.8–2.8
ACS Omega ( IF 3.7 ) Pub Date : 2020-09-25 , DOI: 10.1021/acsomega.0c03749
Ocean Cheung _{1,

2} , Zoltán Bacsik ₁ , Nicolas Fil ₁ , Panagiotis Krokidas _{1,

3} , Dariusz Wardecki _{1,

4,

5} , Niklas Hedin ₁

Affiliation

Zeolites with appropriately narrow pore apertures can kinetically enhance the selective adsorption of CO₂ over N₂. Here, we showed that the exchangeable cations (e.g., Na⁺ or K⁺) on zeolite ZK-4 play an important role in the CO₂ selectivity. Zeolites NaK ZK-4 with Si/Al = 1.8–2.8 had very high CO₂ selectivity when an intermediate number of the exchangeable cations were K⁺ (the rest being Na⁺). Zeolites NaK ZK-4 with Si/Al = 1.8 had high CO₂ uptake capacity and very high CO₂-over-N₂ selectivity (1190). Zeolite NaK ZK-4 with Si/Al = 2.3 and 2.8 also had enhanced CO₂ selectivity with an intermediate number of K⁺ cations. The high CO₂ selectivity was related to the K⁺ cation in the 8-rings of the α-cage, together with Na⁺ cations in the 6-ring, obstructing the diffusion of N₂ throughout the zeolite. The positions of the K⁺ cation in the 8-ring moved slightly (max 0.2 Å) toward the center of the α-cage upon the adsorption of CO₂, as revealed by in situ X-ray diffraction. The CO₂-over-N₂ selectivity was somewhat reduced when the number of K⁺ cations approached 100%. This was possibly due to the shift in the K⁺ cation positions in the 8-ring when the number of Na⁺ was going toward 0%, allowing N₂ diffusion through the 8-ring. According to in situ infrared spectroscopy, the amount of chemisorbed CO₂ was reduced on zeolite ZK-4s with increasing Si/Al ratio. In the context of potential applications, a kinetically enhanced selection of CO₂ could be relevant for applications in carbon capture and bio- and natural gas upgrading.

中文翻译：

Si / Al为1.8-2.8的NaK-ZK-4沸石对CO _2的选择性吸附

具有适当狭窄孔口的沸石可以在动力学上增强CO ₂对N ₂的选择性吸附。在这里，我们表明，沸石ZK-4上的可交换阳离子（例如Na ⁺或K ⁺）在CO ₂选择性中起重要作用。当中间数量的可交换阳离子为K ⁺（其余为Na ⁺）时，Si / Al = 1.8–2.8的NaK ZK-4沸石具有非常高的CO ₂选择性。Si / Al = 1.8的NaK ZK-4沸石具有较高的CO ₂吸收能力和非常高的CO ₂ -N ₂含量选择性（1190）。Si / Al = 2.3和2.8的NaK ZK-4沸石还具有中等数量的K ⁺阳离子，具有更高的CO ₂选择性。高的CO ₂选择性与α-笼的8环中的K ⁺阳离子以及6环中的Na ⁺阳离子有关，从而阻碍了N ₂在整个沸石中的扩散。原位X射线衍射表明，在吸附CO _2时，8环中K ⁺阳离子的位置向α-笼的中心略微移动（最大0.2Å）。当K ⁺的数量增加时，CO ₂ -N _2的选择性有所降低。阳离子接近100％。这可能是由于当Na ⁺的数量接近0％时，8环中K ⁺阳离子的位置发生了变化，从而使N ₂扩散通过8环。根据原位红外光谱，随着Si / Al比的增加，沸石ZK-4s的化学吸附CO ₂量减少。在潜在应用的背景下，从动力学上增强对CO _2的选择可能与碳捕获以及生物和天然气提纯中的应用有关。

更新日期：2020-10-06

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