CO Separation from H₂ via Hydrate Formation in Single-Walled Carbon Nanotubes

Hydrogen is an alternative fuel without generating greenhouse gas or other harmful emissions. Industrial hydrogen production, however, always contains a small fraction of carbon monoxide (CO) (∼0.5-2%) that must be removed for use in fuel cells. Here, we present molecular dynamics simulation evidence on facile separation of CO from H₂ at ambient pressure via the formation of quasi-one-dimensional (Q1D) clathrate hydrates within single-walled carbon nanotubes (SW-CNTs). At ambient pressure, Q1D CO (or H₂) clathrates in SW-CNTs are formed spontaneously when the SW-CNTs are immersed in CO (or H₂) aqueous solution. More interestingly, for the CO/H₂ aqueous solution, highly preferential adsorption of CO over H₂ occurs within the octagonal or nonagonal ice nanotubes inside of SW-CNTs. These results suggest that the formation of Q1D hydrates within SW-CNTs can be a viable and safe method for the separation of CO from H₂, which can be exploited for hydrogen purification in fuel cells.