Hydrogen permeation measurements of partially internally oxidized Pd–Al alloys in the presence and absence of CO

Abstract

Specific permeabilities and diffusion constants for H have been measured in a series of Pd-Al alloy membranes using a new method for activation of the membranes. The membranes have been partially internally oxidized at an elevated temperature before inserting into the apparatus for measuring H 2 permeabilities. If the percent internal oxidation is small relative to the membrane thickness, the diffusion takes place essentially through the unoxidized alloys. The activation energy for diffusion of H increases with atom fraction Al from 23.2 kJ/mol 1/2H 2 (X Al =0) to 25.1 J/mol 1/2H 2 (X Al =0.08). It is shown that the partially oxidized alloys are more resistant to CO poisoning than unoxidized alloys. The resistance of the partially internally oxidized alloys towards poisoning by CO (g) increases and the diffusion constants decrease with X Al .

Effect of metal‐support interface on hydrogen permeation through palladium membranes

“…50 Up to now, Pd-Al alloy formation has been observed upon depositing Pd on both polycrystalline Al surfaces, 51,52 Al films, 53,54 and Al (001) single crystals, and has also been tackled by a variety of different methods, including XRD, 55 X-ray photoelectron spectroscopy, 51,52,56,57 ion scattering, 56,57 thermal desorption spectroscopy, 51,52,57 secondary ion mass spectroscopy, 51,57 CO adsorption 51,52,57,58 and transmission electron microscopy. 59 Meanwhile, Wang et al 60 measured H 2 solubility and diffusivity for Pd-Al alloys and pure Pd at 423-503 K. It was found that Pd-Al alloys possessed lower H 2 solubility and diffusivity than that of pure Pd. Moreover, H 2 solubility and diffusivity decreases with atomic Al fraction increases.…”

Hydrogen solubilities and permeabilities in un-oxidized and partially internally oxidized fcc Pd–Fe and alloys (393–523K)

“…It has been shown by the authors that partial IO of Pd-Al alloys reduces the inhibition effect of CO on the H 2 permeation [15]. For this reason the effect of IO on the Pd-Fe alloys is of interest.…”

“…(Pd 0.77 Ag 0.23 ) (1−x) Fe x alloys will also be investigated because the Pd 0.77 Ag 0.23 alloy is the prime H purification membrane and the presence of small amounts of Fe will allow some partial internal oxidation (IO) which could lead to a greater resistance to gaseous poisons [15].…”

The effect of CO on hydrogen permeation through Pd and through internally oxidized and un-oxidized Pd alloy membranes

“…It has been found [7] that internally oxidized (IOed) Pd-Al alloys have a greater resistance to CO inhibition than either Pd or the un-oxidized Pd-Al alloys. It was also found by the present workers [7] that the degree of CO inhibition increases as the flux increases and therefore a comparison of the degree of CO inhibition of the IOed alloys with Pd or with un-oxidized alloys should be carried out between membranes which have similar fluxes in the absence of CO. More recently it has been noted by Nguyen et al [8] that CO inhibition of a Pd 0.75 Ag 0.23 alloy membrane increases as the thickness of the membrane decreases which is the same as the finding that the inhibition increases with increase of flux. The earlier experiments [7] were carried out employing mainly (H 2 + CO) mixtures.…”