Ultramicropore engineering by dehydration to enable molecular sieving of H2 by calcium trimesate

The high energy footprint of commodity gas purification and ever-increasing demand for gases require new approaches to gas separation. Kinetic separation of gas mixtures through molecular sieving can enable “ideal” separation through molecular size or shape exclusion. Physisorbents must exhibit just the right pore diameter to enable such ideal separation, but the 0.3-0.4 nm range relevant to small gas molecules is hard to control with precision. Herein, we report that dehydration of the ultramicroporous metal-organic framework Ca-trimesate, Ca(HBTC).H2O (H3BTC = trimesic acid), bnn-1-Ca-H2O, affords a narrow pore variant, Ca(HBTC), bnn-1-Ca. Whereas bnn-1-Ca-H2O (pore diameter 0.34 nm) exhibits ultra-high CO2/N2, CO2/CH4 and C2H2/C2H4 binary selectivities, bnn-1-Ca (pore diameter 0.31 nm) offers ideal selectivities for H 2 /CO 2 and H2/N2 under cryogenic conditions. Ca-trimesate, the first physisorbent to exhibit H2 sieving under cryogenic conditions, could be prototypal for a potentially general approach to exert precise control over pore diameter in physisorbents.