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.