Nanostructured Palladium-Doped Silica Membrane Layer Synthesis for Hydrogen Separation: Effect of Activated Sublayers

Palladium doped silica membranes were synthesized by the sol-gel method using two different procedures. The first palladium-doped silica membrane (M1) was synthesized with a coating of four layers of silica-palladium sol. The second membrane (M2) was synthesized with a coating of two silica layers followed by a coating of two silica-palladium layers. Scanning electron microscopy (SEM) proved the formation of uniform γ-alumina interlayers on the supports. SEM results for M1 showed that  synthesis of a membrane with this procedure leads to the formation of crack on the membrane selective layer. Single gas permeation measurements of H2 and N2 were carried out at room temperature, 100 °C and 550 °C. Gas permeation results revealed that Knudsen diffusion was dominant in permeation of these gases through membrane M1 while the dominant mechanism in permeation of gases through  membrane M2 was activated transport which has exhibited different behavior in comparison with M1. This result is due to the activated sublayers of membrane M2. In this case, H2 permeance increases and N2 permeance decreases with increasing temperature, leading to better separation perforamce of membrane M2 over M1 in separation of H2. Therefore, using the activated silica sublayer in the synthesis of M2 can be used as a high potential method to synthesize a selective palladium-doped silica membrane.