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Abstract: Pd, Pd90Ag10, Pd91Au9, Pd78Ag9Au13 and Pd75Ag16Au9 alloy membranes were prepared on vacuum-assisted ZrO2-modified porous stainless steel supports by sequential electroless deposition. The membranes were evaluated for permeability in pure H2 and in an H2S/H2 mixture. The membranes displayed a range of permeabilities in pure H2: Pd90Ag10>Pd78Ag9Au13>Pd~Pd75Ag16Au9>Pd91Au9. On exposure to 100ppm H2S/H2 at 673K for 24h, all membranes lost a significant fraction of their H2 permeabilities: Pd (lost the largest fraction, 85%)>Pd90Ag10>Pd75Ag16Au9>Pd78Ag9Au13>Pd91Au9 (60%). When H2S was removed, the membranes recovered the lost permeability to different extents. The Pd91Au9 and Pd78Ag9Au13 membranes displayed the highest fractional recovery of initial H2 permeability (~80%). But, with its higher initial pure H2 permeability, Pd78Ag9Au13 had the highest absolute H2 permeability after recovery. The microstructure, morphology and bulk composition of H2S-exposed samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). XRD revealed the presence of a bulk Pd4S phase on both Pd and Pd90Ag10, the membranes that recovered the least H2 relative flux after their exposure to H2S. In contrast, bulk sulfides did not form on Pd91Au9 or on PdAgAu ternary alloys. In agreement with the XRD results, EDS did not detect sulfur in the bulk of Pd91Au9 or in either of the ternary alloy samples. Our results show that the addition of Au to the high-permeability PdAg binary membrane results in a PdAgAu ternary membrane that minimizes the permanent H2 flux loss associated with H2S exposure by preventing the formation of thick stable sulfides. [Copyright &y& Elsevier]

Abstract: PdAgAu alloy films were prepared on porous stainless steel supports by sequential electroless deposition. Two specific compositions, Pd83Ag2Au15 and Pd74Ag14Au12, were studied for their sulfur tolerance. The alloys and a reference Pd foil were exposed to 1000H2S/H2 at 623 K for periods of 3 and 30 h. The microstructure, morphology and bulk composition of both non-exposed and H2S-exposed samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). XRD and SEM analysis revealed time-dependent growth of a bulk Pd4S phase on the Pd foil during H2S exposure. In contrast, the PdAgAu ternary alloys displayed the same FCC structure before and after H2S exposure. In agreement with the XRD and SEM results, sulfur was not detected in the bulk of either ternary alloy samples by EDS, even after 30 h of H2S exposure. X-ray photoelectron spectroscopy (XPS) depth profiles were acquired for both PdAgAu alloys after 3 and 30 h of exposure to characterize sulfur contamination near their surfaces. Very low S 2p and S 2s XPS signals were observed at the top-surfaces of the PdAgAu alloys, and those signals disappeared before the etch depth reached ∼10 nm, even for samples exposed to H2S for 30 h. The depth profile analyses also revealed silver and gold segregation to the surface of the alloys; preferential location of Au on the alloys surface may be related to their resistance to bulk sulfide formation. In preliminary tests, a PdAgAu alloy membrane displayed higher initial H2 permeability than a similarly prepared pure Pd sample and, consistent with resistance to bulk sulfide formation, lower permeability loss in H2S than pure Pd. [Copyright &y& Elsevier]