Chemical Stability of MIL-101(Cr) upon Adsorption of SO₂ and NO₂ under Dry and Humid Conditions

A detailed understanding of the chemical stability of metal–organic frameworks (MOFs) in water and acidic and basic solutions currently exists; however, there has been comparatively little investigation into the chemical stability of MOFs in the presence of acid gas species that may be present in industrial settings. MIL-101(Cr), a MOF that is stable in liquid water as well as acidic and basic solutions, was tested for its stability upon exposure to the acid gases sulfur dioxide (SO₂) and nitrogen dioxide (NO₂). Successive breakthrough experiments of both SO₂ and NO₂ show that both gases lower the adsorption capacity of MIL-101(Cr), which is also observed by N₂ physisorption experiments. X-ray photoelectron spectroscopy (XPS) confirms the presence of sulfur and nitrogen species in MIL-101(Cr) after exposure to SO₂ and NO₂ species. In situ infrared spectroscopy experiments suggest that adsorption of SO₂ in MIL-101(Cr) is not completely reversible and that adsorption of NO₂ in MIL-101(Cr) causes some structural degradation similar to what has been previously observed in HKUST-1.