Terephthalic acid (BDC) based metal-organic frameworks (MOFs) including rare-earth 2,5-dioxid-1,4-benzenedicarboxylate (DOBDC), are promising candidates for acid gas separations and adsorption from flue gas streams. However, previous simulations have shown that acid gases (H2O, NO2, and SO2) react with the DOBDC linker by deprotonating a hydroxyl group and protonating the acid gas. The protonation of NO2 to form HONO has been noted in several studies but is challenging to detect experimentally. Computational approaches can provide insight into the likelihood of secondary gas formation. Here, reaction barriers and formation energies of secondary protonated acid gases were evaluated by using both density-functional theory (DFT) and correlated wave-function methods. The formation reaction energies were evaluated for DOBDC and related BDC derivatives to reveal what drives or reduces secondary gas formation. Results indicate that BDC based molecules are less reactive in a trans orientation and that aminated BDCs are more stable than thiols or hydroxyl derivatives. The results show considerations that should be made when designing MOFs not only for acid gas applications, but also for general MOF design.

Effect of linker structure and functionalization on secondary gas formation in metal-organic frameworks

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