The mechanism of preferential binding of gaseous molecules in nanoporous adsorbents is important to understand. Here, Mg-MOF-74 is chosen to study the preferential binding of SOx versus H2O in a complex humid gas stream. It as an extremely well-known and well-studied MOF and the relative ease of synthesis allows for the MOF to be produced in large quantities. Whilst it is known that Mg-MOF-74 endures a structural collapse in water, it enables a structural investigation into the effects of humidity on the binding of species with higher binding energies, such as SOx. Mg-MOF-74 was synthesized under aqueous conditions and subsequently loaded from a complex gas stream of water vapor (RH 26%) and SOx (62-96 ppm). The adsorption studies were carried out at room temperature for 4 days, with a sample taken every 24 hr. Each sample was analyzed by powder X-ray diffraction (PXRD), fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis - mass spectrometry (TGA-MS) and scanning electron microscopy - energy dispersive spectroscopy (SEM-EDX). Crucially, the MOF showed retained crystallinity and peak intensity in the PXRD and after 2 days showed no obvious degradation to the structure. Use of multiple techniques including TGA, identified 10% by weight of SOx species, specifically H2S and SO2, within the MOF. Preferential binding of SOx to the oxophilic metal site of the framework in the presence of competing H2O was confirmed by solid state 1H solid-state NMR.

Preferential binding of SOx versus H2O in Mg-MOF-74 from a humid gas stream

ACS Spring Meeting 2021

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