Process swing adsorption with selective purge gas recirculation (PSA-SPUR): unlocking CO2 capture from flue gas via Zr-MOF adsorbents

Anthropogenic CO₂ emissions demand urgent and efficient carbon capture solutions. This study proposes a synergistic material-process strategy by integrating a tailored zirconium-based metal-organic framework (MOF), UiO-66-(OH)₂, with an innovative Pressure Swing Adsorption process featuring Selective Purge Recirculation (PSA-SPUR) for efficient CO₂ capture from flue gas. We demonstrate that bed productivity in this advanced cycle is governed by CO2 adsorption capacity, the extent of linearity of the CO2 isotherms, and equilibrium selectivity of CO2 over N2, rather than mere static capacity. While benchmark adsorbents like Zeolite 13X suffer from excessive affinity that hinders regeneration, UiO-66-(OH)₂ strikes an optimal balance of isotherm curvature, enabling a high CO₂/N₂ selectivity of 89 and a remarkable working capacity of 1.96 mmol g⁻¹ at 0.15 bar and 298 K. Density Functional Theory (DFT) calculations and GCMC simulations elucidate the molecular mechanism, revealing that the dual hydroxyl groups create a potent yet reversible binding environment through synergistic Zr-μ₃-OH···O and ligand-H···O interactions. By recirculating selective purge gas to enrich the feed, the PSA-SPUR system decouples the inherent purity-recovery trade-off of conventional PSA, theoretically achieving 100% purity and 100% recovery simultaneously. This work provides a conceptual advancement in carbon capture by shifting the focus from maximizing static adsorption to optimizing material-process compatibility.