Fabrication of a thin palladium membrane supported in a porous ceramic substrate by chemical vapor deposition

Abstract

A thin, gas-tight palladium (Pd) membrane was prepared by the counter-diffusion chemical vapor deposition (CVD) process employing palladium chloride (PdCl 2) vapor and H 2 as Pd precursors. A disk-shaped, two-layer porous ceramic membrane consisting of a fine-pore γ-Al 2O 3 top layer and a coarse-pore α-Al 2O 3 substrate was used as Pd membrane support. A 0.5–1 μm thick metallic membrane was deposited in the γ-Al 2O 3 top layer very close to its surface, as verified by XRD and SEM with a backscattered electron detector. The most important parameters that affected the CVD process were reaction temperature, reactants concentrations and top layer quality. Deposition of Pd in the γ-Al 2O 3 top layer resulted in a 100- to 1000-fold reduction in He permeance of the porous substrate. The H 2 permeation flux of these membranes was in the range 0.5–1.0 × 10 −6 mol m −2 s −1 Pa −1 at 350–450°C. The H 2 permeation data suggest that surface reaction steps are rate-limiting for H 2 transport through such thin membranes in the temperature range studied.