Arrhenius Laboratory, Stockholm University, 10691 Stockholm, Sweden.
Phys Chem Chem Phys. 2014 Jan 7;16(1):166-72. doi: 10.1039/c3cp52821a.
Ab initio Molecular Dynamics (AIMD) is used with spatial constraints to estimate the free energy barriers of diffusion for CO2 and N2 gas molecules in zeolite NaA and KA. We investigate the extent to which the diffusion of these gas molecules is hindered, in the two separate cases of a smaller Na(+) ion or a larger K(+) ion blocking the 8-ring pore window. In contrast to classical Molecular Dynamics, AIMD performs these computations accurately and unbiased in the absence of empirical parameterization. Our work has resulted in stable and reliable force profiles. The profiles show that the larger K(+) ion effectively blocks the passage of both CO2 and N2 molecules while the smaller Na(+) ion will allow both molecules to pass. These results are a quantitative demonstration of the concept of pore blocking where we compute the effect, which the size of the respective cation occupying the pore window has on diffusive properties of each gas molecule. Hence, this effect can be altered through ion exchange to fine-tune the functionality of a specific zeolite as a molecular sieve.
运用空间约束的从头分子动力学（AIMD）来估计 CO2 和 N2 气体分子在沸石 NaA 和 KA 中的扩散自由能势垒。我们研究了在较小的 Na(+)离子或较大的 K(+)离子分别阻塞 8 元环孔窗的情况下，这些气体分子的扩散受到多大程度的阻碍。与经典分子动力学不同，AIMD 在没有经验参数化的情况下准确且无偏地进行这些计算。我们的工作得到了稳定可靠的力谱。这些图谱表明，较大的 K(+)离子有效地阻止了 CO2 和 N2 分子的通过，而较小的 Na(+)离子则允许这两种分子通过。这些结果定量地证明了孔阻塞的概念，我们计算了占据孔窗的阳离子的大小对每个气体分子扩散性质的影响。因此，可以通过离子交换来改变这种影响，从而微调特定沸石作为分子筛的功能。
