Mercaptoundecanoic acid capped palladium nanoparticles in a SAPO 34 membrane: a solution for enhancement of H₂/CO₂ separation efficiency.

In this work, the high quality Pd/SAPO 34 membranes were grown on the support using a secondary (seeded) growth hydrothermal technique followed by insertion of 11-mercaptoundecanoic acid capped palladium (MUA-Pd) nanoparticles (NPs) to the membrane surface. For this, first, the indigenous low cost clay-alumina support was treated with poly diallyldimethylammonium chloride (PolyDADMAC) polymer, and subsequently, a seed layer of SAPO 34 crystals was deposited homogeneously in a regular orientation. Since PolyDADMAC is a high charge density cationic polymer, it assisted in reversing the charge of the support surface and produced an attractive electrostatic interaction between the support and zeolite crystals. This may facilitate the zeolite grain orientation in the synthesized membrane layer. Here, the Pd NPs were deposited in the membrane matrix by a simple dip-coating method. After thermal treatment of the Pd/SAPO 34 membrane, the defects were formed because of the removal of the structure-directing agent (SDA) from the zeolite pores but the presence of Pd NPs, which were entrapped inside the nonzeolitic pores and clogged the defects of the membrane. Field emission scanning electron microscopy (FESEM) and elemental mapping of the membrane cross-section confirmed that most of the Pd NPs were deposited at the interface of the membrane and the support layer which may increase the membrane efficiency, i.e., separation factor, as well as permeability of H2 through the membrane. As the membrane structure was associated with the oriented crystal, the pores were more aligned and permeation adequacy of H2 through the membrane enhanced. These membranes have a relative hydrogen permeance of 14.8 × 10(-7) mol·m(-2)·s(-1)·Pa(-1). The selectivity of H2/CO2 based on single gas permeation was 10.6, but for the mixture gas (H2/CO2 55:45), the H2/CO2 mixture separation factor increased up to 20.8 at room temperature. It is anticipated that this technique may be useful for making a defect free membrane and also a hydrogen selective Pd loaded membrane with lower cost (as the quantity of Pd is low) which can be utilized for a "clean energy" related application.