Regulating the Si/Al ratio of GIS zeolite with bulky primary particles for selective CO₂ capture from hydrocarbons

Carbon dioxide (CO₂) capture from hydrocarbons using low-energy adsorption separation techniques is a promising alternative to conventional low-temperature distillation, but limited by the shortness of low-cost and efficient physical adsorbent, especially for the direct acetylene (C₂H₂) purification because of their very similar size and physiochemical properties. In this work, GIS zeolites with tunable Si/Al ratio were synthesized in an unusual acid co-hydrolysis route to enable the formation of large-sized primary particles, which greatly reduce the outside surface adsorption to enhance the sieving effect of 8-membered ring microchannels. The obtained GIS zeolites afforded high CO₂ uptake (3.5 mmol g^-1 and 128 cm³ cm^-3) while negligible adsorption towards other gases including C₂H₂, N₂, CH₄, C₂H₄, and C₂H₆, showing the remarkable selective CO₂ adsorption from a CO₂-C₂H₂(N₂ or CH₄) mixture with the CO₂/C₂H₂ (50/50 v/v) selectivity up to 8.5 × 10¹⁰. Breakthrough experiments revealed the favorable dynamic separation behavior with better performance on the sample with the comparatively high Si/Al ratio of 3.1. The CO₂ adsorption at 195 K and structural refinement results demonstrated that the excellent separation performance was attributed to the less Na⁺ ions inside the microchannels providing more inner space for the accommodation of guest molecules.