Observation of Binding and Rotation of Methane and Hydrogen within a Functional Metal–Organic Framework

The key requirement for a portable
store of natural gas is to maximize
the amount of gas within the smallest possible space. The packing
of methane (CH4) in a given storage medium at the highest
possible density is, therefore, a highly desirable but challenging
target. We report a microporous hydroxyl-decorated material, MFM-300­(In)
(MFM = Manchester Framework Material, replacing the NOTT designation),
which displays a high volumetric uptake of 202 v/v at 298 K and 35
bar for CH4 and 488 v/v at 77 K and 20 bar for H2. Direct observation and quantification of the location, binding,
and rotational modes of adsorbed CH4 and H2 molecules
within this host have been achieved, using neutron diffraction and
inelastic neutron scattering experiments, coupled with density functional
theory (DFT) modeling. These complementary techniques reveal a very
efficient packing of H2 and CH4 molecules within
MFM-300­(In), reminiscent of the condensed gas in pure component crystalline
solids. We also report here, for the first time, the experimental
observation of a direct binding interaction between adsorbed CH4 molecules and the hydroxyl groups within the pore of a material.
This is different from the arrangement found in CH4/water
clathrates, the CH4 store of nature.