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.