Evaluation of the Stability of Diamine-Appended Mg(dobpdc) Frameworks to Sulfur Dioxide.

Diamine-appended Mg(dobpdc) (dobpdc = 4,4'-dioxidobiphenyl-3,3'-dicarboxylate) metal-organic frameworks are a promising class of CO adsorbents, although their stability to SO─a trace component of industrially relevant exhaust streams─remains largely untested. Here, we investigate the impact of SO on the stability and CO capture performance of dmpn-Mg(dobpdc) (dmpn = 2,2-dimethyl-1,3-propanediamine), a candidate material for carbon capture from coal flue gas. Using SO breakthrough experiments and CO isobar measurements, we find that the material retains 91% of its CO capacity after saturation with a wet simulated flue gas containing representative levels of CO and SO, highlighting the robustness of this framework to SO under realistic CO capture conditions. Initial SO cycling experiments suggest dmpn-Mg(dobpdc) may achieve a stable operating capacity in the presence of SO after initial passivation. Evaluation of several other diamine-Mg(dobpdc) variants reveals that those with , (1°,1°) diamines, including dmpn-Mg(dobpdc), are more robust to humid SO than those featuring , (1°,2°) or , (1°,3°) diamines. Based on the solid-state N NMR spectra and density functional theory calculations, we find that under humid conditions, SO reacts with the metal-bound primary amine in 1°,2° and 1°,3° diamine-appended Mg(dobpdc) to form a metal-bound bisulfite species that is charge balanced by a primary ammonium cation, thereby facilitating material degradation. In contrast, humid SO reacts with the free end of 1°,1° diamines to form ammonium bisulfite, leaving the metal-diamine bond intact. This structure-property relationship can be used to guide further optimization of these materials for CO capture applications.