Formation of CH₄ Hydrate in a Mesoporous Metal–Organic Framework MIL-101: Mechanistic Insights from Microsecond Molecular Dynamics Simulations

The formation of CH 4 hydrate in a mesoporous metal–organic framework MIL-101 is investigated by microsecond molecular dynamics simulations. CH 4 hydrate is observed to form preferentially in the outer space of MIL-101 cavities rather than inside the cavities; only when the hydrate formation is nearly complete in the outer space can stable hydrate form in MIL-101 cavities. The underlying reason is revealed to be the easy dissociation of small hydrate clusters formed in the nanospace of the cavities, because of the diffusion of CH 4 molecules out of the cavities into the outer space. Compared with dry MIL-101, the CH 4 storage capacity of H 2 O-saturated MIL-101 is drastically reduced as the cavities are occupied by H 2 O. When oversaturated with H 2 O, however, extra H 2 O molecules in the outer space of the cavities can form considerable CH 4 hydrate, significantly promoting CH 4 storage capacity. This study provides important mechanistic insights into the formation mechanism and process of CH 4 hydrate in MIL-101 and will facilitate the design of emerging materials for energy storage.