Preferential SOx Adsorption in Mg-MOF-74 from a Humid Acid Gas Stream.

The preferential\nadsorption of SO_<i>x</i> versus\nwater in Mg-MOF-74 from a humid SO_<i>x</i> gas\nstream has been investigated via materials studies and nuclear magnetic\nresonance (NMR). Mg-MOF-74 has been synthesized and subsequently loaded\nsimultaneously with water vapor and SO_<i>x</i> (62–96 ppm) in an adsorption chamber at room temperature\nover a time period of 4 days with a sample taken every 24 h. Each\nsample was analyzed by powder X-ray diffraction (PXRD), Fourier transform\ninfrared spectroscopy, thermogravimetric analysis (TGA)–mass\nspectrometry, and scanning electron microscopy–energy-dispersive\nspectroscopy. The metal–organic framework (MOF) showed retained\ncrystallinity and peak intensity in PXRD, and after 2 days, it showed\nno obvious degradation to the structure. Use of multiple techniques,\nincluding TGA, identified 10% by weight of SO_<i>x</i> species, specifically H₂S and SO₂, within\nthe MOF. ¹H solid-state NMR shows a substantial reduction\nof H₂O when SO_<i>x</i> is present,\nwhich is consistent with SO_<i>x</i> preferentially\nbinding to the oxophilic metal site of the framework. After 14 weeks\naging, the sulfur remains present in the three-dimensional MOF, with\nonly half being desorbed after 23 weeks in air.