Acid gases (NO2, SO2) commonly occur in complex chemical streams, and metal-organic frameworks (MOFs) have been extensively evaluated for their separation and removal. During competitive gas adsorption, secondary reactive gas species can form inside the MOF pores potentially causing framework degradation. Identifying the reaction mechanisms between nanoconfined gases and the MOF framework is key for the design of next generation adsorbents. Herein, ab initio molecular dynamics (AIMD) simulations are used for the first time to calculate competitive adsorption of binary and tertiary mixed acid gases (NO2, SO2, H2O) and in-pore reaction mechanisms for a series of rare earth (RE)-DOBDC (RE = rare earth; DOBDC = 2,5-dihdroxyterephthalic acid) MOFs. Spontaneous formation of nitrous acid (HONO) occurs via deprotonation of the MOF organic linker, DOBDC for NOx mixtures. The mixed monodentate and bidentate DOBDC coordination to the metal clusters allows for proton transfer from the linker to the NO2, altering MOF durability. Additionally, competitive adsorption of SO2 and NO2 in dry and humid conditions is evaluated based on competing binding mechanisms between the acid gases and the MOF, including the formation of additional reactive species. The evaluation of nanoconfined tertiary acid gas mixtures in RE-DOBDC MOFs demonstrates a methodology that can be applied for prediction of future gas interactions in emerging nanoporous materials for acid gas separations.

Competitive adsorption and reactivity of acid gases in rare earth metal organic frameworks

ACS Spring 2022

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