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

Abstract

Developing molecular sieves is vital, energy-saving, but very challenging for gas separations in the petrochemical industry. Current molecular sieves reported for inverse CO₂/C₂H₂ separation are very scarce and suffer from low CO₂ capacity and poor diffusion within the restricted nanopores. Herein, we report an electrostatically driven size-sieving of CO₂ from C₂H₂ in a porous cation-gated molecular sieve (Na-RHO) with high CO₂ 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 C₂H₂ due to the electrostatically driven sieving effect, and large pore cavities provide enough pore spaces to take up large amount of CO₂ 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 CO₂/C₂H₂ selectivity (3.35 × 10⁶) and CO₂ uptake capacity (188.0 cm³ cm^-3) at ambient conditions. Breakthrough experiments show that Na-RHO can directly separate CO₂ impurity from CO₂/C₂H₂ mixtures, with the highest dynamic selectivity (70.4) and C₂H₂ 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.