General introduction of zeolite based CO2 capture

https://doi.org/10.1039/D2SC00702A

“Zeolites are a famous category of inorganic porous materials with well-defined and stable structures, large surface areas, and various active sites, which have broad applications in the fields of catalysis, ion exchange, adsorption/separation and pharmaceuticals.¹⁰ The large CO₂ adsorption capacity, high structural stability and controllable polarity give zeolites great potential for application in gas adsorption and separation of CO₂-containing gas mixtures.¹¹ Zeolites preferentially adsorb molecules with large dipole and quadrupole moments, especially CO₂ (13.4 × 10⁻⁴⁰ C m² quadrupole moment), because the frameworks possess strong electric fields, and thus fairly high CO₂ adsorption uptake and selectivity over N₂ (4.7 × 10⁻⁴⁰ C m² quadrupole moment) at low pressure, making them promising candidates for applications.^4a,12 Various factors can influence the adsorption capacity and selectivity of zeolites for CO₂, such as framework composition,¹³ topologies,¹⁴ channel systems,¹⁵ pore size dimensions,¹⁶ pore volumes,¹⁷ exchanged cations,¹⁸ isomorphous heteroatom substitutions,¹⁹ and numbers and distributions of active sites that are related to acidities and polarities.^12b,20 It is worth noting that the similar kinetic diameters of CO₂ (0.33 nm) and N₂ (0.36 nm) make kinetic separation very challenging.^9,21 Recently, some small pore zeolites with 8-membered ring windows have been spotlighted and confirmed to be excellent CO₂ adsorbents, since the effective size of their 8-rings can be tuned to ensure the passage of CO₂, but to hinder the slightly larger N₂ molecule, leading to high CO₂/N₂ selectivity.^4a,14,20,22 As a notable example, the low-pressure separation of CO₂ from N₂ by SSZ-13 zeolite (CHA framework topology) was studied in both acidic and copper-exchanged forms, which exhibited unconventional high selectivity (>70) evaluated by the ideal adsorbed solution theory under ideal conditions for industrial CO₂/N₂ separations.^4a The high CO₂ uptake of aluminosilicate zeolites is partly due to their high electrical field gradients. However, aluminosilicate zeolites adsorb CO₂ very vigorously, limiting the ease of their use in cyclic adsorption processes.^12c,23“