Molecular specificity in neutron imaging: the case of hydrogen adsorption in metal organic frameworks

Neutron imaging is the technique of choice for a number of in situ and operando applications, where a high penetration power is required. White-beam neutron imaging and energy-resolved Bragg edge imaging are successful techniques, the former for the detection of specific elements characterized by strong neutron attenuation and the latter for studying crystal structures. Here we discuss the capabilities of energy-selective neutron imaging taking advantage of the incoherent and inelastic scattering interactions in hydrogenous materials, as a way to obtain molecular-specific information about the composition of a given sample. While few examples from the available literature are discussed, a worked example is presented based on new experimental data on molecular-hydrogen adsorption and conversion in the HKUST-1 metal organic framework. Energy-resolved neutron imaging can provide molecular-specific information in hydrogenous materials. At thermal neutron energies, cross sections are sensitive to hydrogen dynamics through incoherent and inelastic contributions to neutron scattering.