Ultramicropore Engineering by Dehydration to Enable Molecular Sieving of H2by Calcium Trimesate

The high energy footprint of commodity gas purification and increasing demand for gases require new approaches to gas separation. Kinetic separation of gas mixtures through molecular sieving can enable separation by molecular size or shape exclusion. Physisorbents must exhibit the right pore diameter to enable separation, but the 0.3-0.4 nm range relevant to small gas molecules is hard to control. Herein, 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/N-2, CO2/CH4, and C2H2/C(2)H(4)binary selectivity, bnn-1-Ca (pore diameter 0.31 nm) offers ideal selectivity for H-2/CO(2)and H-2/N(2)under cryogenic conditions. Ca-trimesate, the first physisorbent to exhibit H(2)sieving under cryogenic conditions, could be a prototype for a general approach to exert precise control over pore diameter in physisorbents.