Pd-based binary and ternary alloy membranes: Morphological and perm-selective characterization in the presence of H2S

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 H-2 and in an H2S/H-2 mixture. The membranes displayed a range of permeabilities in pure H-2: Pd90Ag10 > Pd78Ag9Au13 > Pd similar to Pd75Ag16Au9 > Pd91Au9. On exposure to 100 ppm H2S/H-2 at 673 K for 24 h, all membranes lost a significant fraction of their H-2 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 H-2 permeability (similar to 80%). But, with its higher initial pure H-2 permeability, Pd78Ag9Au13 had the highest absolute H-2 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 to, the membranes that recovered the least H-2 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 H-2 flux loss associated with H2S exposure by preventing the formation of thick stable sulfides. (C) 2013 Elsevier B.V. All rights reserved.