Synthesis and characterization of Pd membranes on alumina-modified porous stainless steel supports

Palladium composite membranes have been obtained by deposition of Pd on alumina-modified stainless steel supports. The preparation procedure involves deposition of a double layer of γ-alumina (γ-Al2O3) on the support by dip coating, followed by drying and calcination, activation of the modified support, deposition of palladium by electroless plating. SEM/EDS and Auger spectroscopy analysis, coupled with sputtering allowed the identification of critical issues and a proper re-elaboration of the preparation procedure. It has been found that γ-Al2O3 completely covers the support surface determining a significant reduction of surface rugosity. Activation, however, even if performed inside the γ-Al2O3 pH stability range, determines the partial dissolution of alumina; this phenomenon is enhanced while decreasing pH value. Moreover, Pd seeds, which catalyze subsequent Pd deposition, are not distributed evenly on the surface. As a consequence of the above observations, membrane preparation has been modified by introducing a pre-activation of the γ-Al2O3 external layer, consisting of the addition of palladium chloride to the alumina gel and palladium reduction in sodium boron hydride solution after calcination.