The growth of nanosized zeolite nuclei inside the pinholes of ultra-thin Pd composite membranes

Abstract

The ultra-thin Pd composite membrane has found extensive industrial applications because of its exceptionally high hydrogen permselectivity and permeability. The thickness of the Pd membrane is continuously reduced to pursue lower costs, but pinholes inevitably appear on the surface of ultra-thin Pd membranes, which severely reduce its hydrogen selectivity and limit its commercial viability. Distinct from the formation of a zeolite layer through conventional hydrothermal synthesis, this study proposes an innovative and convenient “region growing method” that in situ grows nanosized zeolite nuclei inside the pinholes of the ultra-thin Pd composite membrane under mild conditions. After ion exchange, the zeolite crystal transforms from NaA into KA, with the channel width reaching 0.28 nm, thereby blocking the passage of all gases, including H₂. Following this modification, the Pd composite membrane achieves an H₂/N₂ selectivity exceeding 160 000 without increasing the membrane thickness. The modified membrane also exhibits excellent lifespan and stability, allowing for continuous stable operation for nearly 10 000 hours and more than 70 rapid heating and cooling cycles. As this approach is no longer limited by high-pressure conditions, it has great potential for mass-scale applications.