Cheung Ocean, Bacsik Zoltán, Fil Nicolas, Krokidas Panagiotis, Wardecki Dariusz, Hedin Niklas
Department of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University, Stockholm SE 106 91, Sweden.
Nanotechnology and Functional Materials, Department of Materials Science and Engineering, Uppsala University, Uppsala SE 75121, Sweden.
ACS Omega. 2020 Sep 25;5(39):25371-25380. doi: 10.1021/acsomega.0c03749. eCollection 2020 Oct 6.
Zeolites with appropriately narrow pore apertures can kinetically enhance the selective adsorption of CO over N. Here, we showed that the exchangeable cations (e.g., Na or K) on zeolite ZK-4 play an important role in the CO selectivity. Zeolites NaK ZK-4 with Si/Al = 1.8-2.8 had very high CO 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 CO uptake capacity and very high CO-over-N selectivity (1190). Zeolite NaK ZK-4 with Si/Al = 2.3 and 2.8 also had enhanced CO selectivity with an intermediate number of K cations. The high CO 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 N 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 CO, as revealed by in situ X-ray diffraction. The CO-over-N 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 N diffusion through the 8-ring. According to in situ infrared spectroscopy, the amount of chemisorbed CO was reduced on zeolite ZK-4s with increasing Si/Al ratio. In the context of potential applications, a kinetically enhanced selection of CO could be relevant for applications in carbon capture and bio- and natural gas upgrading.
具有适当窄孔孔径的沸石可以在动力学上增强对 CO 相对于 N 的选择性吸附。在此，我们表明沸石 ZK - 4 上的可交换阳离子（例如 Na 或 K）在 CO 选择性方面起着重要作用。当可交换阳离子的中间数量为 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 选择性。Si/Al = 1.8 的 NaK ZK - 4 沸石具有高的 CO 吸附容量和非常高的 CO 对 N 的选择性（1190）。Si/Al = 2.3 和 2.8 的 NaK ZK - 4 沸石在中间数量的 K 阳离子时也具有增强的 CO 选择性。高 CO 选择性与 α 笼 8 元环中的 K 阳离子以及 6 元环中的 Na 阳离子有关，它们阻碍了 N 在整个沸石中的扩散。原位 X 射线衍射表明，吸附 CO 后，8 元环中 K 阳离子的位置向 α 笼中心略微移动（最大 0.2 Å）。当 K 阳离子数量接近 100%时，CO 对 N 的选择性有所降低。这可能是由于当 Na 的数量趋于 0%时，8 元环中 K 阳离子位置的移动，使得 N 能够通过 8 元环扩散。根据原位红外光谱，随着 Si/Al 比的增加，ZK - 4 沸石上化学吸附的 CO 量减少。在潜在应用方面，动力学增强的 CO 选择对于碳捕获以及生物气和天然气升级应用可能具有重要意义。
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