Organic template residues confined in silicalite-1 zeolite membranes for tuning pore structures and boosting H2/CO2 separation

Abstract

Silicalite-1 zeolite membranes were successfully activated at 300–350 °C in a hydrogen atmosphere. FTIR, TGA, and N2 adsorption-desorption characterizations confirmed that the amount of the organic structure directing agent (OSDA) residue in silicalite-1 zeolite channels was tunable. The H2-calcined membrane showed a lower gas permeance than that of the air-calcined membrane due to the partial pore blockage by the OSDA residue. The permeance of H2 and CO2 increased with increasing temperature, showing an activated diffusion-like mechanism. The activation energies for the permeation of H2 and CO2 were in the range of 1.63–4.15 and 0.76–5.90 kJ mol−1, respectively, which confirmed the reduced average membrane pore size and different pore surface chemistry due to the presence of the OSDA residue in the membrane. Significant interactions between CO2 molecules and OSDA residues confined in the membrane resulted in a notably lower CO2 permeance compared to N2 and CH4, despite CO2 having a smaller kinetic diameter. Enhanced H2/CO2 selectivity in the silicalite-1 zeolite membrane, featuring confined OSDA residue, was attributed to the reduction in membrane pore size and the fine-tuning of pore surface chemistry.