Neutron scattering holds many opportunities for obtaining unique information concerning the porous-solid adsorbent (host) as well as host-adsorbate (host-guest) system. Measurement of structure and dynamics using neutron scattering, across length and time scales pertinent to these systems (also possible at the same time), has been exploited for the better understanding of guest binding in the host and separation mechanisms, as well as the host’s response to adsorption, all of which are key to progressing the application of such systems in CCS.

Information about both host and host-guest structure, which yields details of the structural response of the host to adsorption, the location of the guest in the host, and guest-host interaction, are important to determining structure-property relations. As neutron diffraction intensity does not reduce with scattering angle, relatively more fine structural detail is gained than using X-ray diffraction, providing important detail concerning the guest-host and guest-guest interactions. The iso- topically-dependent structural information afforded by neutrons allows different contrast between parts of the host framework and/or guest to be gained, providing many advantages for such structural investigations. Examples include distinguish­ing between guests such as N2, O2, and CO2, and obtaining details of both the host’s ligands and metal centres, as well as guests, even within a MOF containing heavy-metal atoms and guests containing light atoms. Additionally, the information obtained can be tuned through isotopic substitution, such as in determining the molecular orientations of CH4 within a host using the isotopically-substituted CD4, where D is deuterium (2H),

The dynamic information obtained through neutron scattering is also isotopically dependent, and spectroscopic neutron techniques allow direct measurement of the local environment and the diffusional transport of the guest within the host. Both structure and dynamics can be measured at the same time, enabling insights into the geometry of the guest motion, in turn allowing the details of the mechanism of diffusion of the guest within the host to be gained.

In situ methods are central in the analysis of MOFs for guest separation and storage applications. Although in situ X-ray single crystal and powder diffraction studies of CO2 in MOFs facilitate the understanding of the functional mechanism of MOFs for CCS applications [28—30], in situ neutron-scattering methods have sig­nificant advantages over X-ray studies of MOF-guest systems, with the penetrating power of neutrons being central to this. Neutrons easily penetrate the often-complex sample environments required for control over temperature of the host at the same time as gas delivery, covering easily the range of temperatures from the relatively cold (about -263 °C) conditions required to “lock in” guests and determine accurate structural details, to the more moderate temperatures required to replicate working post-, pre-, and oxyfuel combustion, as well as natural gas-sweetening conditions (40-75 °C). The relatively high penetrating power of neutrons also allows for the analysis of bulk samples, mg—gram quantities, providing information about the more industrially-relevant “bulk” properties of the material. The bulk-scale analysis also aids in accurately dosing the sample with a known number of guest molecules to determine in detail the nature of their interaction with the host.