Synthesis of hierarchical porous Zeolite-Y for enhanced CO₂ capture

In the present study, a facile and one step approach has been developed for the synthesis of hierarchical porous zeolite-Y using bifunctional cationic polymer, polydiallyldimethyl ammonium chloride (PDDA) as a mesopore directing template. The effects of various synthesis parameters such as hydrothermal reaction temperature, time, amount of PDDA and NaOH were systematically investigated to produce crystalline and hierarchical zeolite-Y crystals (PDYs). All the synthesized zeolite-Y samples were characterized by XRD, FT-IR, SEM, EDAX, TEM, TGA, CO₂-TPD and Nitrogen adsorption-desorption measurements. The characterization results showed that the zeolite-Y samples synthesized at optimized ratios of PDDA/Al₂O₃ and NaOH/Al₂O₃ exhibited higher crystallinity, higher BET surface area and larger total pore volume in comparison to the sample synthesized in the absence of the template (ZY). Interestingly, the hierarchical porous zeolite-Y samples (PDY-7) displayed substantial enhancement in CO₂ adsorption capacity (5.40 mmol/g) at 298 K and 100 kPa as compared to the non-templated one (ZY) (4.5 mmol/g). The effective improvement in CO₂ adsorption performance of PDY samples is attributed to the existence of interconnected micro-meso channel network, the higher total pore volume and higher concentration of acid-base sites (due to the lower Si/Al ratio). Owing to the higher CO₂ adsorption capacity, the PDY samples also displayed high equilibrium selectivity for CO₂ over N₂ (~250) as well as over CH₄ (~110) at 298 K_. The enhanced CO₂ adsorption capacity combined with the high CO₂ adsorption selectivity renders the hierarchical zeolite-Y an excellent contender for the efficient CO₂ capture.