Theoretical Chemistry Institute and Department of Chemistry, University of Wisconsin─Madison, 1101 University Avenue, Madison, Wisconsin 53706, United States.
School of Chemical & Biomolecular Engineering, Georgia Institute of Technology, 311 Ferst Drive NW, Atlanta, Georgia 30332, United States.
J Am Chem Soc. 2021 Nov 3;143(43):18061-18072. doi: 10.1021/jacs.1c06321. Epub 2021 Oct 22.
Zeolitic imidazolate frameworks (ZIFs) are promising materials for industrial process separations, but recent literature reports have highlighted their vulnerability to acid gases (e.g., SO, CO, NO, HS), often present in practical applications. While previous work has documented the widely varying stability behavior of many ZIFs under varying (humid and dry) acid gas environments, efforts to explain or correlate these experimental observations via empirical descriptors have not succeeded. A key observation is that ZIF-71 (RHO topology) is an extraordinarily stable ZIF material, retaining both structure and porosity under prolonged humid SO exposure whereas many other well-known ZIFs with different linkers and topologies (such as ZIF-8) were shown to degrade. Through a combination of hybrid quantum mechanics/molecular mechanics (QM/MM) based methods and statistical mechanical models, we successfully explain this important experimental observation via atomistic investigations of the reaction mechanism. Our holistic approach reveals an ∼9 times lower average defect formation rate in ZIF-71 RHO compared to ZIF-8 SOD, leading to the conclusion that the observed experimental stability of this material rises from kinetic effects. Moreover, our analysis reveals that differing stability of the two materials is determined by the of acid gas molecules, which is difficult to capture using empirical descriptors. Our results suggest wider applicability of the present approach, toward identifying tuned functional groups and topologies that move the acid gas distributions away from more reactive sites and thus allow enhanced kinetic stability.
沸石咪唑酯骨架（ZIFs）是工业过程分离的有前途的材料，但最近的文献报道强调了它们对酸性气体（例如 SO、CO、NO、HS）的脆弱性，这些气体通常存在于实际应用中。虽然之前的工作已经记录了许多 ZIFs 在不同（湿和干）酸性气体环境下广泛变化的稳定性行为，但通过经验描述符解释或关联这些实验观察的努力尚未成功。一个关键的观察结果是 ZIF-71（RHO 拓扑）是一种非常稳定的 ZIF 材料，在长时间暴露于湿 SO 下仍保持结构和孔隙率，而许多其他具有不同连接体和拓扑结构的知名 ZIFs（如 ZIF-8）则被证明会降解。通过结合混合量子力学/分子力学（QM/MM）方法和统计力学模型，我们通过对反应机制的原子级研究成功地解释了这一重要的实验观察。我们的整体方法揭示了 ZIF-71 RHO 中平均缺陷形成速率比 ZIF-8 SOD 低约 9 倍，这导致了一个结论，即该材料观察到的实验稳定性源于动力学效应。此外，我们的分析表明，两种材料稳定性的不同取决于酸性气体分子的插入，这很难用经验描述符来捕捉。我们的结果表明，目前的方法具有更广泛的适用性，可以确定经过调整的功能基团和拓扑结构，使酸性气体分布远离更活跃的部位，从而提高动力学稳定性。
