Evaluation of the Stability of Diamine-Appended Mg2(dobpdc) Frameworks to Sulfur Dioxide

Diamine-appended Mg2(dobpdc) (dobpdc4- = 4,4 '- dioxidobiphenyl-3,3 '-dicarboxylate) metal-organic frameworks are a promising class of CO2 adsorbents, although their stability to SO2-a trace component of industrially relevant exhaust streams-remains largely untested. Here, we investigate the impact of SO2 on the stability and CO2 capture performance of dmpn-Mg2(dobpdc) (dmpn = 2,2-dimethyl-1,3-propanediamine), a candidate material for carbon capture from coal flue gas. Using SO2 breakthrough experiments and CO2 isobar measurements, we find that the material retains 91% of its CO2 capacity after saturation with a wet simulated flue gas containing representative levels of CO2 and SO2, highlighting the robustness of this framework to SO2 under realistic CO2 capture conditions. Initial SO2 cycling experiments suggest dmpn-Mg2(dobpdc) may achieve a stable operating capacity in the presence of SO2 after initial passivation. Evaluation of several other diamine-Mg2(dobpdc) variants reveals that those with primary,primary (1 degrees,1 degrees) diamines, including dmpn-Mg2(dobpdc), are more robust to humid SO2 than those featuring primary,secondary (1 degrees,2 degrees) or primary,tertiary (1 degrees,3 degrees) diamines. Based on the solid-state 15N NMR spectra and density functional theory calculations, we find that under humid conditions, SO2 reacts with the metal-bound primary amine in 1 degrees,2 degrees and 1 degrees,3 degrees diamine-appended Mg2(dobpdc) to form a metal-bound bisulfite species that is charge balanced by a primary ammonium cation, thereby facilitating material degradation. In contrast, humid SO2 reacts with the free end of 1 degrees,1 degrees 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 CO2 capture applications.

Automated summary

In this study, the stability and CO2 capture performance of diamine-appended Mg2(dobpdc) metal-organic frameworks in the presence of SO2 were investigated. It was found that the materials with primary,primary diamines exhibited better stability to humid SO2. The reaction between SO2 and the primary,secondary or primary,tertiary diamines resulted in material degradation, while the reaction with primary,primary diamines did not affect the metal-diamine bond.