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Pd-based membranes offer energy efficiency and economic advantages, providing a promising route for hydrogen separation and recovery from several streams. Alloying Pd with other elements increases its resistance to corrosive gases while improving H 2 permeability. This study investigated the permselective properties of PdNiAu membranes with different Ni contents (17, 23, and 27 at.% Ni) in pure H 2 and under CO/He/H 2 and H 2 S/H 2 mixtures. The permselective properties were evaluated at different temperatures (573–723 K) and pressure differences across the membrane (ΔP: 10–100 kPa). The membranes studied exhibited promising H 2 permeation properties; the highest permeability at 673 K and 100 kPa was obtained with the membrane containing 23 at.% Ni (2.1 × 10−8 mol m−1 s−1 Pa−0.5). All membranes exhibited high H 2 /N 2 selectivity (>10,000). Regarding chemical stability, the membranes with 23 and 27 at.% Ni, showed high tolerance to inhibition by CO and H 2 S. These results suggest that increasing Ni improves membrane performance in streams containing CO or S; however, the high chemical resistance of the membranes could be attributed to both Ni and Au. [Display omitted] • PdNiAu membranes showed potential for H 2 purification from pollutant streams. • The highest permeability (2.1 × 10−8 mol m−1 s−1 Pa−0.5) was obtained at 23 at.% Ni. • Membranes with high Ni content showed high resistance to inhibition by CO. • The H 2 S exposure did not significantly affect the performance of the PdNiAu membranes. [ABSTRACT FROM AUTHOR]

PdNiAu-based composite membranes were obtained through sequential electroless deposition, varying their composition by modifying the Ni deposition time. After annealing at high temperature, a single phase with FCC structure was obtained in all the membranes, showing homogeneous alloy composition. A decrease in the lattice parameter was evident as the Ni content increased in the alloy. The permselective properties of the membranes were evaluated at different temperatures and pressures. The results showed that H 2 permeance decreased as the Ni composition increased in the film and increased as the lattice parameter increased. The best performance was obtained with the membrane containing 29 at.% Ni (11.40 × 10−4 mol m−2 s−1 Pa−0.5), even higher than that reported for pure Pd. The membrane with higher Ni content (54 at.%) and lower permeance (0.20 × 10−4 mol m−2 s−1 Pa−0.5 at 723 K) overcame the performance of some Ni-containing membranes previously reported. The membranes showed high stability for several days at high temperatures. [Display omitted] • PdNiAu membranes with different Ni compositions were obtained. • H 2 permeance increased with increasing the lattice parameter of the alloy. • The membrane containing 29% at. Of Ni showed the highest H 2 permeance. [ABSTRACT FROM AUTHOR]

PdCuAu ternary alloy samples with different composition were synthesized on top of ZrO2-modified porous stainless steel disks by the sequential electroless deposition technique. The structure, morphology and bulk composition of the samples were characterized by X-ray diffraction (XRD), scanning electron microscopy and energy dispersive X-ray spectroscopy (EDX). Complete alloy formation with a pure fcc phase for the Pd71Cu26Au3, Pd70Cu25Au5 and Pd67Cu24Au9 samples and a bcc structure for the Pd62Cu36Au2 and Pd60Cu37Au3 samples were obtained upon annealing at 500 °C for 120 h as revealed by XRD. A combination of low-energy ion scattering (LEIS) and X-ray photoelectron spectroscopy (XPS) was used to investigate the surface properties of the PdCuAu alloys. XPS results confirmed alloy formation under the annealing conditions. XPS analysis also revealed that the near-surface regions of the alloys became enriched in Pd with respect to the bulk composition determined by EDX. In contrast, LEIS and angle-resolved XPS analyses showed that the top-most surface layers in all samples were copper-rich compared with the bulk composition. This high Cu surface concentration could impart resistance to bulk sulfide formation to the PdCuAu alloy membranes. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

PdCuAu ternary alloy membranes with different component compositions were synthesized by sequential electroless deposition of components onto porous stainless steel substrates. The ternary with the highest Au content, Pd 69 Cu 14 Au 17 , exhibited the highest hydrogen permeation flux, comparable to that of a Pd 91 Au 9 membrane. Upon exposure to 100 ppm H 2 S/H 2 at 673 K for 24 h, all PdCuAu membranes experienced flux reductions of ~55%, followed by recovery to ~80% of the initial hydrogen flux upon reintroduction of pure hydrogen at 400 °C. Complete flux recovery after H 2 S exposure required hydrogen treatment at 500 °C. X-ray diffraction (XRD) analysis of the H 2 S-exposed PdCuAu membranes revealed fcc alloy structure with no evidence of bulk sulfide formation. In agreement with the XRD results, sulfur was not detected in the bulk of H 2 S-exposed samples by energy dispersive spectroscopy (EDS). However, analysis of H 2 S-exposed PdCuAu alloys by X-ray photoelectron spectroscopy (XPS) depth profiling revealed low, but measureable, amounts of sulfur in the near-surface region, about 10 nm in depth. The depth profiles of samples after hydrogen recovery treatment showed significantly reduced sulfur content. These results indicate that H 2 S exposure causes flux loss in PdCuAu alloys through a surface-poisoning mechanism, and that the surface sulfide can be removed—and flux recovered—by high temperature treatment in hydrogen. [ABSTRACT FROM AUTHOR]

The surface properties of Ni/MgAl2O4 catalysts doped with Ce or Pr were analyzed by XPS after treatment in an inert and reductive atmosphere at 400 °C. The Ce-promoted solids presented the Ce3+/Ce4+ couple on the surface even after treatment in a reductive atmosphere, H2(5%)/Ar. The promotion effect of Ce on these solids could be associated with their participation on the carbon deposition-removal mechanism. Pr-doped catalysts showed a very high concentration of Pr3+ under a reductive atmosphere and the redox behavior associated with the carbon removal could be partially inhibited or become slower. The size of the Ni0 particles after both an inert and a reductive atmosphere was estimated by XPS intensity ratio using the model proposed by Davis. The results obtained from the Davis model showed that an important increase occurred in Ni particle size after treatment in H2(5%)/Ar for the Pr-promoted solids. The metal sintering under reductive atmosphere could be the reason for the higher loss of activity of the Pr-doped solids under reforming conditions. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

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: PdRu films were successfully synthesized on top of non-porous stainless steel supports by electroless co-deposition. The effect of synthesis variables on morphology, substrate adherence, bulk and surface composition was studied. The microstructure and morphology of the samples were analyzed by X-ray diffraction and scanning electron microscopy. Homogeneous and defect-free PdRu films were obtained employing baths at low pH, moderate to high agitation speeds, high concentration of hydrazine, using EDTA as a stabilizer and temperatures near 50°C. Films characterized by X-ray photoelectron spectroscopy showed Pd segregation after annealing the sample at 400°C in H2 (5%)/Ar in the load-lock chamber of the spectrometer. The optimized conditions were employed to synthesize a PdRu composite membrane on top of a tubular porous stainless steel substrate (0.1μm grade). Hydrogen permeation was measured over a 350–450°C temperature range and a trans-membrane pressure up to 100kPa. The PdRu membrane showed good performance with a hydrogen permeability of 6.5×10−9 molm−1 s−1 Pa−0.5 and a selectivity higher than 1700. [Copyright &y& Elsevier]

Abstract: A ZSM-5 membrane synthesized on a stainless steel porous tube was used for the separation of p-xylene from its isomers, m- and o-xylene. The membrane was prepared by secondary growth on the outer surface of the support. The permeation regime through the membrane was described by a combination of adsorption–diffusion steps. In order to examine the durability of the membrane, a sequence of three thermal cycles was conducted. N2 permeation measurements together with scanning electron microscopy (SEM) observations were the tools used to detect whether or not cracks developed after exposure to the xylene isomers up to 400°C. After 1000h on stream, the membrane was selective to p-xylene, the N2 permeance fluxes remained unchanged and the SEM micrographs did not reveal any discontinuity. [Copyright &y& Elsevier]

The effect of the support shape on the deposition of ZrO 2 by the vacuum-assisted dip-coating method was studied. Disc-shaped and tubular porous stainless steel substrates were used to obtain ZrO 2 coated supports for the synthesis of PdAu alloy composite membranes. The microstructure of the ZrO 2 modified supports was evaluated by scanning electron microscopy and confocal laser microscopy. Besides, a qualitative assessment of the porosity and roughness of the porous substrates was performed by confocal laser microscopy. Dense and continuous palladium-alloy films were deposited on top of the modified tubes after thirteen ZrO 2 deposition-calcination cycles. Cross-section EDS mapping and XRD diffraction analysis showed that a complete PdAu alloy formation was obtained even after annealing at 723 K in hydrogen stream during 5 days. [ABSTRACT FROM AUTHOR]

NaA zeolite membranes were synthesized on top of both disk and tubular porous stainless steel substrates by the secondary growth method. The support seed stage was optimized, considering the seed synthesis conditions and the deposition method. The formation of the NaA zeolite on both the membrane and the residual powder collected at the bottom of the vessel after synthesis was corroborated by X-ray diffraction (XRD). Scanning electron microscopy (SEM) revealed the formation of a film with well-defined crystals with a cubic morphology characteristic of the NaA zeolite. The support modification with 3-aminopropyltriethoxysilane improved the morphology and stability of the NaA zeolite membranes synthesized on top of porous stainless steel substrates. When vacuum was applied only in the last hydrothermal synthesis stage, a smooth zeolite layer was obtained on top of porous stainless steel supports. The single gas (H 2 , N 2 , CO 2 and CH 4 ) and mixture (H 2 /N 2 and H 2 /CH 4 ) perm-selective properties of the tubular membranes were evaluated as a function of temperature and pressure. Separation factors higher than the Knudsen coefficient were obtained in all membranes. The single gas H 2 and CO 2 permeation flux of the membranes increased with temperature indicating a preponderance of the activated diffusion over the Knudsen diffusion. The higher H 2 /CO 2 ideal separation factors were 7.6 and 5.6 for the more selective tubular membranes, at 453 K and 100 kPa. [ABSTRACT FROM AUTHOR]

Novel PdNiAu ternary samples were successfully developed by sequential electroless deposition of the pure metals. The structure, composition, and morphology of the synthesized samples were analyzed by X-ray diffraction, Scanning Electron Microscopy, and energy-dispersive X-ray Spectroscopy. XRD analysis revealed that the metal deposition order (Ni→Pd→Au or Pd→Ni→Au) strongly affects the formation of a single and homogeneous FCC phase. By means of X-ray Photoelectron Spectroscopy, Pd-enrichment to the surface was evidenced in the sample with lower Ni content. The optimized procedure allowed synthesizing the Ni 29 Pd 64 Au 7 _PSS composite membrane, which exhibited a hydrogen permeance slightly higher than that reported for pure Pd. [Display omitted] • PdNiAu alloys were successfully synthesized by sequentially electroless deposition. • The metal deposition order strongly affects the formation of a single FCC phase. • The Ni 29 Pd 64 Au 7 _PSS membrane shown higher H 2 permeability than pure Pd. [ABSTRACT FROM AUTHOR]

PdAu composite membranes were applied for the preparation of PtNaA-PdAu catalytic membranes for hydrogen production from the water gas shift reaction. In the first stage, the deposition of NaA zeolite on top of the PdAu alloys was optimized. Functionalization employing a 1.0 v/v % 3-aminopropyltriethoxysilane solution prior to both seeding and hydrothermal synthesis allowed obtaining a homogeneous and complete PdAu alloy surface coverage. Even though the NaA zeolite coverage decreased the pure hydrogen permeance at 623 K and 50 kPa in comparison with a PdAu membrane, the resistance to a CO containing stream was higher. From direct incorporation of Pt during the zeolite synthesis, a homogeneous, well-intergrown PtNaA zeolite coverage on top of a PdAu alloy membrane was obtained. PtNaA catalytic tubular membranes were evaluated in the water gas shift reaction at 673 K. The membranes were active and stable under reaction conditions, without evidence of methane formation. Image 1 • NaA zeolite coverage increases the resistance to CO containing streams of PdAu membranes. • Encapsulated PtNaA catalyst was effectively deposited on top of PdAu membranes. • The catalytic membranes were active for the WGS reaction, without methane formation. [ABSTRACT FROM AUTHOR]

Using the electroless deposition technique with different deposition sequences, it was possible to obtain a single phase PdAgAu ternary alloy after treatment at 773 K during 7 days. Despite the order of deposition, the samples exhibited similar hydrogen permeation flux at the same temperature and pressure. In the presence of CO, the PdAgAu ternary alloy membranes showed a lower inhibition on the hydrogen permeance compared with the binary PdAu alloy at 623 and 673 K. On the contrary, under CO 2 containing streams, the ternary alloy showed a higher inhibition with a complete hydrogen recovery after removing CO 2 from the stream. When H 2 S was introduced in the 13% CO 2 /13% Ar/74% H 2 stream, a higher permeance decrease was observed on both the PdAu and PdAgAu alloy membranes. After removal of H 2 S, a hydrogen recovery of 60% and 76% was measured for the PdAu and PdAgAu membranes, respectively. Pd surface segregation was observed on the Pd 82 Ag 15 Au 3 –873 K-5 d and the Pd 78 Au 6 Ag 16 –773 K-7 d samples upon exposure to CO containing streams. Instead, silver surface segregation was observed by XPS after exposing the PdAgAu ternary alloy to CO 2 containing streams. [ABSTRACT FROM AUTHOR]

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]