Potassium amino acid–based DES–zeolite hybrids for CO₂ capture: Balancing viscosity, pore accessibility, and high-temperature stability

The rational design of hybrid sorbents requires mechanistic understanding of how molecular interactions influence pore accessibility and CO₂ uptake. In this study, potassium amino acid–based deep eutectic solvents (DESs) were prepared from K-AMALA (Potassium salt of α-methylalanine) with monoethanolamine (MEA) or tetraethylenepentamine (TEPA) and impregnated into zeolite 13X. Comprehensive characterization (FT-IR, DSC, EA, TGA, BET, SEM-EDS) confirmed effective impregnation without loss of zeolite crystallinity, while revealing partial pore blockage at high loadings. The optimized hybrid, AM11 13 × 25, achieved a CO₂ uptake of 0.589 mmol·g⁻¹ at 353 K under 15 vol% CO₂, representing a ∼51% improvement over pristine 13X (0.389 mmol·g⁻¹). Mechanistic analysis showed that moderate DES loading enhances chemical affinity while preserving pore accessibility, whereas excessive loading (50 wt%) causes severe blockage. TEPA-based hybrids exhibited higher intrinsic reactivity due to multiple amine sites, but viscosity and steric effects limited mass transfer. These results establish that the balance between amine density, viscosity, and pore accessibility governs capture efficiency in DES–zeolite hybrids. Demonstrating framework integrity to ≥ 773 K and operability near hot-flue-gas temperatures with careful volatile management, these materials represent promising candidates for CO₂ separation from hot flue gases in cement, steel, and power industries. Future studies on cyclic stability, regeneration energy, and impurity tolerance will be essential for industrial deployment.