The first-principles calculations have been adapted to probe the possible degradation mechanism of Zeolitic Imidazolate Frameworks (ZIFs) induced by acid gases in humid environment. ZIFs are an important class of porous crystalline metal−organic framework (MOF) materials due to their potential impact in diverse industrial applications ranging from gas storage/separation to catalysis. The formation of dangling linker (LD) and linker-vacancy (Lvac) defects in bulk ZIF-8 was shown to be thermodynamically plausible under experimentally relevant temperatures. [Zhang et al., J. Phys. Chem. Lett. 2016, 7, 459] Such defects might affect stability and reactivity of MOF materials. In this work we considered LD formation as a first step in degradation induced by common adsorbates expected in realistic working environment of ZIFs: H2O, H2S, SO2, SO3, H2SO3 and H2SO4. In general calculated reaction energies and associated barriers were found to be significantly lower for ZIF-2 than ZIF-8. The steric effect promoted by the bulky ligand of the latter leads to its greater stability. However, we also find that sulfurous acid-induced degradation of ZIF-8 is catalyzed by small amount of sulfuric acid. Finally we investigated the adsorption strength of aforementioned molecules in defective bulk (with Lvac) of ZIFs. Our calculations reveal that acid gases bind only slightly stronger to ZIF-2 than ZIF-8, suggesting that in this case steric effect is less important due to existence of the open metal sites.

Computational investigation of acid-gas induced degradation mechanism of zeolitic imidazolate frameworks

254th National Meeting (2017)

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