Chemistry in confined spaces: Reactivity of the Zn-MOF-74 channels

TL;DR

This study reveals that Zn-MOF-74 channels facilitate the conversion of water and CO into formic acid without external catalysts, highlighting new catalytic possibilities within MOF structures and potential for industrial applications.

Contribution

It demonstrates for the first time that water and CO react inside MOF-74 channels to produce formic acid without external catalysts, using combined spectroscopy and ab initio methods.

Findings

Water dissociates at metal centers in MOF-74.

CO reacts with dissociated water to produce formic acid.

Reaction occurs inside MOF channels without external catalysts.

Abstract

Using infrared spectroscopy combined with ab initio methods we study reactions of H$_2$O and CO inside the confined spaces of Zn-MOF-74 channels. Our results show that, once the water dissociation reaction H$_2$O$\;\rightarrow\;$OH+H takes place at the metal centers, the addition of 40 Torr of CO at 200 $^{\circ}$C starts the production of formic acid via OH+H+CO$\;\rightarrow\;$HCO$_2$H. Our detailed analysis shows that the overall reaction H$_2$O+CO$\;\rightarrow\;$HCO$_2$H takes place in the confinement of MOF-74 without an external catalyst, unlike the same reaction on flat surfaces. This discovery has several important consequences: It opens the door to a new set of catalytic reactions inside the channels of the MOF-74 system, it suggests that a recovery of the MOF's adsorption capacity is possible after it has been exposed to water (which in turn stabilizes its crystal structure), and it produces the important industrial feedstock formic acid.