Sulfur resistant Pd and Pd alloy membranes by phosphidation

Novel ultra-thin Pd and Pd-alloy (Pd–Ag, Pd–Cu) membranes, with a phosphorus component, were prepared on a porous hollow fiber α-alumina support. The aim was to study the effect of the presence of a P additive on the behavior of the membranes towards sulfur poisoning. To incorporate P in the structure, the membranes were exposed to PH 3 as a gaseous phosphorous source. The performance and sulfur resistance of the membranes with and without P was evaluated by measuring the hydrogen permeance and the H 2 /N 2 selectivity at 673 K before and during exposure to a gas mixture of 100 ppm H 2 S in H 2 , and also after regeneration in H 2 . The membranes were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM), both before exposure to H 2 S and after exposure/regeneration. XRD shows no detectable amounts of sulfur or phosphorus compounds in any of the exposed or P-treated membranes respectively. XPS indicates that S was located on the surface of the H 2 S/H 2 treated Pd and Pd–Ag membranes. No S was detected on the surface of the Pd–Cu membranes indicating that no irreversible S compounds were formed in the latter. P was also detected on the surface of the P-treated membranes. The presence of phosphorus lowered the hydrogen permeance and H 2 /N 2 selectivity; however it drastically improved the Pd-alloy membranes' capacity of recovery in H 2 after H 2 S poisoning. The Pd–Cu membrane recovered only part of its H 2 permeance after regeneration, going from 11.2×10 −7 mol m −2 s −1 Pa −1 (as-prepared) to 2.3×10 −7 mol m −2 s −1 Pa −1 , while in the presence of P the H 2 permeance varied from 5.2×10 −7 mol m −2 s −1 Pa −1 (as-prepared) to 6.5×10 −7 mol m −2 s −1 Pa −1 and its H 2 /N 2 selectivity increased from 30,000 to 40,000. Similarly, the Pd–Ag membrane recovered better in the presence of P going from 17×10 −7 mol m −2 s −1 Pa −1 (as-prepared) to 6.3×10 −7 mol m −2 s −1 Pa −1 in contrast to 52×10 −7 mol m −2 s −1 Pa −1 (as-prepared) to 5.9×10 −7 mol m −2 s −1 Pa −1 in the absence of P. SEM images show that in the absence of P, more cracks and pinholes are visible on the surface of the H 2 S/H 2 exposed membranes. The presence of P produces more homogeneous surfaces and less segregation, conferring a structural integrity to the membrane by suppressing the formation of cracks and pinholes.