Insights into the structure of mixed CO₂/CH₄ in gas hydrates

The exchange of carbon dioxide for methane in natural gas hydrates is an attractive approach to harvesting CH₄ for energy production while simultaneously sequestering CO₂. In addition to the energy and environmental implications, the solid solution of clathrate hydrate (CH₄)_1-x(CO₂)_x·5.75H₂O provides a model system to study how the distinct bonding and shapes of CH₄ and CO₂ influence the structure and properties of the compound. High-resolution neutron diffraction was used to examine mixed CO₂/CH₄ gas hydrates. CO₂-rich hydrates had smaller lattice parameters, which were attributed to the higher affinity of the CO₂ molecule interacting with H₂O molecules that form the surrounding cages, and resulted in a reduction in the unit-cell volume. Experimental nuclear scattering densities illustrate how the cage occupants and energy landscape change with composition. These results provide important insights on the impact and mechanisms for the structure of mixed CH₄/CO₂ gas hydrate.