Direct Air Capture (DAC) is a critical negative carbon technology that extracts dilute CO₂ (only 400–420 ppm) from ambient air to mitigate greenhouse gas emissions. Unlike flue gas carbon capture with high CO₂ partial pressure, DAC faces severe challenges including ultra-low CO₂ concentration, abundant water vapor coexistence, low adsorption selectivity, and frequent temperature swing adsorption (TSA) cycles. Conventional adsorbents such as activated carbon and amine-modified silica suffer from low CO₂ capacity, high regeneration energy consumption, and poor hydrothermal stability. Functionalized zeolite molecular sieves, represented by Li-LSX, Na-X, 13X, SSZ-13, and amine-impregnated hierarchical zeolites, exhibit outstanding CO₂/N₂ and CO₂/H₂O separation performance, stable cyclic adsorption-desorption properties, and low manufacturing cost, which are recognized as promising solid adsorbents for industrial DAC systems. This paper systematically introduces CO₂ capture mechanism, classification of DAC zeolites, structure-performance correlation, cyclic regeneration characteristics, and industrial application optimization strategies, providing theoretical and engineering guidance for large-scale DAC device design.

Global carbon neutrality targets drive the rapid development of negative emission technologies. Direct Air Capture (DAC) can directly remove atmospheric CO₂ independent of emission sources, realizing carbon removal from distributed and historical carbon footprints. The core bottleneck restricting DAC commercialization lies in efficient, durable, and low-cost CO₂ adsorbents.

Ambient air contains massive N₂, O₂ and saturated water vapor, while CO₂ only accounts for ~0.04 vol%. The adsorbent must selectively capture trace CO₂ without excessive water co-adsorption, and sustain thousands of thermal swing cycles without capacity attenuation. Liquid amine solvents have high capture capacity but suffer from severe solvent volatilization, high corrosion and huge heat consumption during regeneration.

Zeolite molecular sieves possess uniform microporous channels, adjustable cation sites, and controllable surface polarity. Alkali metal-exchanged X-type zeolites, chabazite SSZ-13, and amine-functionalized hierarchical zeolites show strong affinity toward CO₂ via electrostatic interaction and quadrupole adsorption, showing great application potential in DAC low-concentration CO₂ capture scenarios.

CO₂ molecule carries permanent quadrupole moment, which can form strong electrostatic attraction with extra-framework metal cations inside zeolite micropores. Two core adsorption pathways dominate DAC working conditions:

Water vapor competes with CO₂ for cation active sites, leading to declined CO₂ loading capacity. High-silica zeolites reduce water affinity, while cation exchange optimizes CO₂ competitive adsorption performance under humid air, which is the key design direction of DAC molecular sieves.

Li-LSX is prepared by complete ion exchange of Na-LSX zeolite with lithium ions. Small-radius Li⁺ provides high charge density, forming strong adsorption sites for CO₂ quadrupoles.