Electrostatically Driven Size‐Sieving of Carbon Dioxide From Acetylene Enabled by a Cation‐Gated Molecular Sieve

Abstract

ABSTRACT Developing molecular sieves is vital, energy‐saving, but very challenging for gas separations in the petrochemical industry. Current molecular sieves reported for inverse CO 2 /C 2 H 2 separation are very scarce and suffer from low CO 2 capacity and poor diffusion within the restricted nanopores. Herein, we report an electrostatically driven size‐sieving of CO 2 from C 2 H 2 in a porous cation‐gated molecular sieve (Na‐RHO) with high CO 2 capacity and fast diffusion. Na‐RHO features large pore cavities (10.7 Å) interconnected by small Na + ‐gated pore windows (3.4 Å), in which the Na + ‐gated pore windows enable a complete size‐exclusion of C 2 H 2 due to the electrostatically driven sieving effect, and large pore cavities provide enough pore spaces to take up large amount of CO 2 with fast diffusion. Such an electrostatically driven molecular‐sieving mechanism for Na‐RHO was studied by gas sorption isotherms and theoretical calculations, leading to both the record‐high CO 2 /C 2 H 2 selectivity (3.35 × 10 6 ) and CO 2 uptake capacity (188.0 cm 3 cm −3 ) at ambient conditions. Breakthrough experiments show that Na‐RHO can directly separate CO 2 impurity from CO 2 /C 2 H 2 mixtures, with the highest dynamic selectivity (70.4) and C 2 H 2 productivity (150.6 L kg −1 ) by far. This work provides a new strategy for designing more efficient molecular sieves with high gas capacity and diffusion for gas separations.