Combined aperture widening and strong polarization in Li+-exchanged mordenite for efficient direct air capture of CO2

Mordenite (MOR) is a widely recognized zeolite for direct air capture (DAC) of CO 2 , attributed to its high adsorption capacity and low adsorption heat. However, current approaches to promote Na + enrichment in 8-member ring channel (8-MRz) of MOR through regulating the Si/Al ratio or controlling Al distribution are constrained by synthesis controllability and cost, limiting further adsorption capacity improvements. Here, we demonstrate a straightforward and effective modification of Na-MOR via Li + -exchange, improving its performance for DAC of CO 2 . Due to its higher charge-to-size ratio compared to Na + , Li + concurrently enlarges aperture size and enhances pore polarity of 8-member ring side pocket (8-MRy). This synergistic spatial and energetic interplay resulted in Li 0.90 Na-MOR exhibiting faster kinetics and a higher CO 2 adsorption capacity (1.42 mmol g −1 ) at 400 ppm compared to Na-MOR (1.02 mmol g −1 ). In situ diffuse reflectance infrared fourier transform spectra (DRIFTS) and density functional theory (DFT) analyses confirm that Li + exchange augments charge density within the confined space of 8-MRy, promoting stable co-adsorption of multiple CO 2 molecules. This work advances the understanding of confinement effects on CO 2 adsorption and paves the way for advanced adsorbent design.