Computational Studies on Holey TMC 6 (TM = Mo and W) Membranes for H 2 Purification.

The purification of hydrogen (H 2 ) has been a vital step in H 2 production processes such as steam-methane reforming. By first-principle calculations, we revealed the potential applications of holey TMC 6 (TM = Mo and W) membranes in H 2 purification. The adsorption and diffusion behaviors of five gas molecules (including H 2 , N 2 , CO, CO 2 , and CH 4 ) were compared on TMC 6 membranes with different phases. Though the studied gas molecules show weak physisorption on the TMC 6 membranes, the smaller pore size makes the gas molecules much more difficult to permeate into h-TMC 6 rather than into s-TMC 6 . With suitable pore sizes, the s-TMC 6 structures not only show an extremely low diffusion barrier (around 0.1 eV) and acceptable permeance capability for the H 2 but also exhibit considerably high selectivity for both H 2 /CH 4 and H 2 /CO 2 (>10 15 ), especially under relatively low temperature (150-250 K). Moreover, classical molecular dynamics simulations on the permeation process of a H 2 , CO 2 , and CH 4 mixture also validated that s-TMC 6 could effectively separate H 2 from the gas mixture. Hence, the s-MoC 6 and s-WC 6 are predicted to be qualified H 2 purification membranes, especially below room temperature.