(189l) Competitive Adsorption of Toxic Gases in a Humid Environment: Insights from Density Functional Theory

Toxic gases such as ammonia, phosphine, and methyl bromide, are commonly used in industry and agriculture, which places workers at risk of accidental exposure. Most widely used filtration methods rely on activated carbon, which has low capacity and selectivity for these gases. However, in recent years, researchers have looked to other porous materials, such as metal-organic frameworks (MOFs), as sorbents for toxic gases. [1] One benefit of using MOFs is they can be tailored to specific adsorption applications by adding functional groups or metal sites which increase the MOF’s affinity for the target molecules. [2]

We used density functional theory to study interactions of ammonia, phosphine, arsine, and methyl bromide with 33 metal catecholates in order to examine periodic trends in the binding strength between the gases and metals. [3]

We find markedly different behavior in ammonia than in phosphine and arsine due to different processes governing the adsorption despite the apparent similarity of these molecules. Phosphine and arsine adsorption is primarily driven by electron density being donated from the adsorbate molecule to the metal atom, while ammonia binding involves both some electron donation and a significant Coulombic attraction between the negatively-charged N atom and the positively-charged metal atom. We also studied simultaneous adsorption of methyl bromide and water on metal catecholates. While late transition metals such as Pt and Au have the highest affinity and selectivity for MeBr, we find that alkaline earth metals such as Ca are more resistant to the presence of humidity.

We will discuss how these different adsorption mechanisms are manifested through trends in binding strength across the periodic table, as well as the implications for adsorption of industrially relevant toxic gases in humid environments.

1. S. Bobbitt, M. L. Mendonca, A. J. Howarth, T. Islamoglu, J. T. Hupp, O. K. Farha, R. Q. Snurr, Chemical Society Reviews, 46, 3357-3385, 2017
2. Yu, P.Ghosh, and R. Q. Snurr,Dalton Transactions, 41, 3962-3973, 2012
3. S. Bobbitt, R. Q. Snurr, Ind. & Eng. Chem. Res., 56, 14324-14336, 2017