  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.
