Zeolitic imidazolate frameworks (ZIFs) are promising candidate for gas storage and separations, but their vulnerability to acid gases (e.g., SO2, CO2, NO2, H2S) inhibiting them from practical applications. Previous work has reported the widely varying stability behavior of many ZIFs under different acid gas environments. A key observation is that ZIF-71 (RHO topology) shows an extraordinary stability under prolonged humid SO2 exposure, whereas many other well-known ZIFs (such as ZIF-8) were shown to degrade. Most importantly, efforts to explain or correlate these experimental observations via empirical descriptors have not succeeded. Through the combination of a hybrid quantum mechanics/molecular mechanics (QM/MM) method and statistical mechanical modeling, we successfully explain this important experimental observation, showing that the average defect formation rate in ZIF-71 is ~9 times lower as compared to ZIF-8 SOD. Our calculation reveals that differing stability of the two materials is determined by the distributions of acid gas molecules.

Origins of acid-gas stability behavior in zeolitic imidazolate frameworks

ACS Spring 2022

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