Understanding and Controlling Water Stability of MOF-74

Date

2018-06-01

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Publisher

Royal Society of Chemistry

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Abstract

Metal organic framework (MOF) materials in general, and MOF-74 in particular, have promising properties for many technologically important processes. However, their instability under humid conditions severely restricts practical use. We show that this instability and the accompanying reduction of the CO2 uptake capacity of MOF-74 under humid conditions originate in the water dissociation reaction H2O → OH + H at the metal centers. After this dissociation, the OH groups coordinate to the metal centers, explaining the reduction in the MOF's CO2 uptake capacity. This reduction thus strongly depends on the catalytic activity of MOF-74 towards the water dissociation reaction. We further show that - while the water molecules themselves only have a negligible effect on the crystal structure of MOF-74 - the OH and H products of the dissociation reaction significantly weaken the MOF framework and lead to the observed crystal structure breakdown. With this knowledge, we propose a way to suppress this particular reaction by modifying the MOF-74 structure to increase the water dissociation energy barrier and thus control the stability of the system under humid conditions.

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Keywords

Dissociation, Crystals, Catalysts, Humidity, Water

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"This work was entirely supported by Department of Energy Grant No. DE–FG02–08ER46491. It further used resources of the Oak Ridge Leadership Computing Facility at Oak Ridge National Laboratory, which is supported by the Office of Science of the Department of Energy under Contract DE–AC05– 00OR22725."

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©2016 The Royal Society of Chemistry. This article may not be further made available or distributed.

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