Preparation of a palladium alloy composite membrane supported in a porous stainless steel by vacuum electrodeposition

Pinhole-free palladium/nickel (Pd/Ni) alloy membranes deposited on a porous stainless steel (SUS) support have been fabricated. The deposition was made by vacuum electrodeposition technique which could produce the alloy film less than 1 μm thick. This technique allows for the Pd/Ni alloy by employing Pd/Ni complex reagent, and typical Pd/Ni plating had compositions of 78% Pd and 22% Ni. In order to make the surface smooth and enhance the adhesive bond between the top layer and the substrate, a nascent porous SUS disk was treated sequently with submicron nickel powder and CuCN solution. The important parameters that can affect deposition were pore size, defects, and surface roughness of substrate. The membranes were characterized by permeation experiments with hydrogen and nitrogen at temperatures ranging from 623 to 823 K and pressures from 10.3 to 51.7 cmHg. The composite membranes prepared in this technique yielded excellent separation performance for hydrogen: hydrogen permeance of 5.79×10⁻² cm³/cm² cmHg s and hydrogen/nitrogen (H₂/N₂) selectivity was 4700 at 823 K.     

Synthesis of coin-like hollow carbon and performance as Pd catalyst support for methanol electrooxidation

The coin-like hollow carbon (CHC) has been synthesized by only using ethanol as the carbon source with a novel Mg/NiCl₂ catalytic system via a facile solvothermal method for the first time. The CHC synthesized at optimized conditions shows an average thickness of less than 154 nm and the coin diameter of 1–3 μm. The CHC is characterized by SEM, TEM, XRD and electrochemical techniques. Pd on CHC (denotes as Pd/CHC) electrocatalysts are prepared for methanol oxidation in alkaline media. The Pd/CHC electrocatalyst gives a mass activity of 2930 A g⁻¹ Pd for methanol oxidation against 870 A g⁻¹ Pd on Pd/C electrocatalyst. One main reason for the higher mass activity of the Pd/CHC is the higher electrochemical active surface area (EASA) of the Pd/CHC.     

Preparation of palladium membranes from the reaction of Pd(C3H3)(C5H5) with H2: wet-impregnated deposition

A new technique to prepare a palladium membrane for high-temperature hydrogen permeation was developed: Pd(C₃H₃)(C₅H₅) an organometallic precursor reacted with hydrogen at room temperature to decompose into Pd crystallites. This reaction together with sintering treatment under hydrogen and nitrogen in sequence resulted in the formation of dense films of pure palladium on the surface of the mesoporous stainless steel (SUS) support. Under H₂ atmosphere the palladium membrane could be sintered at 823 K to form a skin layer inside the support pores. The hydrogen permeance was 5.16×10⁻² cm³ cm⁻² cm Hg⁻¹ s⁻¹ at 723 K. H₂/N₂ selectivity was 1600 at 723 K.     

Electrochemical behavior of CO2 reduction on palladium nanoparticles: Dependence of adsorbed CO on electrode potential

The electrochemical reduction of CO₂ is strongly influenced by both the applied potential and the surface adsorption status of the catalyst. In this work a gas diffusion electrode (GDE) coated with Pd nanoparticles/carbon black (Pd/XC72) was used to study the electrochemical reduction of CO₂. Cyclic voltammetric (CV) analysis of Pd/XC72 between 1.5 V and − 0.6 V (vs. RHE) shows the formation of intermediates and the blocking of hydrogen absorption on the Pd nanoparticles (NPs) under a CO₂ atmosphere. The relationships between the Faradaic efficiency/current density and the applied potential reveal that the onset potential of CO formation is around − 0.4 V. Moreover, the presence of adsorbed CO was confirmed through CV analysis of Pd/XC72 under CO₂ and CO/He atmospheres. This demonstrates that H atoms and CO intermediates co-adsorb on the surface of the Pd NPs at an applied potential of around − 0.4 V. When the applied potential is more negative than − 0.6 V, adsorption of CO intermediates on the surface of the Pd NPs becomes dominant.     

Effect of hydrogen-sulfide on the hydrogen permeance of palladium–copper alloys at elevated temperatures

The hydrogen permeance of several 0.1 mm thick Pd–Cu alloy foils (80 wt.% Pd–20 wt.% Cu, 60 wt.% Pd–40 wt.% Cu and 53 wt.% Pd–47 wt.% Cu) was evaluated using transient flux measurements at temperatures ranging from 603 to 1123 K and pressures up to 620 kPa both in the presence and absence of 1000 ppm H₂S. Sulfur resistance, as evidenced by no significant change in permeance, was correlated with the temperatures associated with the face-centered-cubic crystalline structure for the alloys in this study. The permeance of the body-centered cubic phase, however, was up to two orders of magnitude lower when exposed to H₂S. A smooth transition from sulfur poisoning to sulfur resistance with increasing temperature was correlated with the alloy transition from a body-centered-cubic structure to a face-centered-cubic structure.     

Increasing the efficiency of silicon and aluminum extraction from Volclay by a water iteration treatment for the synthesis of MCM-41 nanomaterials

This work aims to reduce the prices of a wide range of nanomaterials which are unreachable in the industry by using natural sources as silicon and aluminum precursors. In a previous work, silicon and aluminum have been extracted from Volclay after applying the alkaline fusion process at 550 °C, and a water treatment of this fused clay by adopting a weight ratio (1:4, fusion mass:H₂O) to synthesize Al-MCM-41 nanomaterials. In this study, the weight ratio of fusion mass:H₂O was increased to 1:8 to synthesize a highly structurally ordered MCM-41 under the same reaction conditions. The Al-MCM-41 nanomaterials are investigated by inductively coupled plasma optical emission spectrometry (ICP–OES), powder X-ray diffraction (XRD), N₂ adsorption–desorption measurements and scanning electron microscopy (ESEM). As a result, the increase in the weight ratio fusion mass:H₂O generates more silica and aluminum, which allows the formation of well-ordered MCM-41 nanomaterials with high pore volume (0.70 cm³/g), high surface area (1044 m²/g), and uniform mesoporous diameter (3.67 nm); as a consequence, the increase in the weight ratio fusion mass:H₂O leads to an increase in the mass of Al-MCM-41 (9.3 g for 1:8 compared to 5 g for 1:4), whereas the yield of production of mesoporous materials increases to 86%.     

Comparative theoretical study of the structure and bonding of propyne on the Pt(1 1 1) and Pd(1 1 1) surfaces

The interaction of propyne with the Pt(1 1 1) and Pd(1 1 1) surfaces has been studied by means of the generalised gradient approach of density functional theory using periodic slab models. For both surfaces, the most stable adsorption mode of propyne is di-σ/π mode where the hydrocarbon is σ-bonded to two metal atoms with some additional π bonding to a third adjacent surface atom. The adsorption geometry is a highly distorted propyne with the C₁ and C₂ in a nearly sp² hybridisation. Two equivalent surface structures have been found on Pt and Pd. These correspond to the adsorption on the fcc or hcp hollow sites. The adsorption energies on Pt(1 1 1) and Pd(1 1 1) are predicted to be ∼−197 and −161 kJ mol⁻¹, respectively. The electronic factors that control the chemisorption have been analysed by means of the projected density of states.     

Preconcentration procedure trace amounts of palladium using modified multiwalled carbon nanotubes sorbent prior to flame atomic absorption spectrometry: 1st Nano Update

A method for preconcentration of palladium at trace level on modified multiwalled carbon nanotubes columns and determination by flame atomic absorption spectrometry (FAAS) has been developed. Multiwalled carbon nanotubes (MWCNTs) were oxidized with concentrated HNO₃ and the oxidized multiwalled carbon nanotubes were modified with 5-(4′-dimethylamino benzyliden)-rhodanine, and then were used as a solid sorbent for preconcentration of Pd(II) ions. Factors influencing sorption and desorption of Pd(II) ions were investigated. The sorption of Pd(II) ions was quantitative in the pH range of 1.0–4.5, whereas quantitative desorption occurs with 3.0 mL 0.4 mol L^?1 thiourea. The amount of eluted palladium was measured using flame atomic absorption spectrometry. The effects of experimental parameters, including sample flow rate, eluent flow rate, and eluent concentration were investigated. The effect of coexisting ions showed no interference from most ions tested. The proposed method permitted a large enrichment factor (about 200). The relative standard deviation of the method was ±2.73% (for eight replicate determination of 2.0 μg mL^?1 of Pd(II)) and the limit of detection was 0.3 ng mL^?1. The method was applied to the determination of Pd(II) in water, road dust, and standard samples.     

Morphological study of supported thin Pd and Pd–25Ag membranes upon hydrogen permeation

Morphological change of Pd and Pd–25Ag membranes supported by V–15Ni alloy upon hydrogen permeation was investigated in the temperature range 423–673 K. The supported Pd–25Ag membrane exhibited higher resistance to hydrogen-induced cracking and grain growth than the supported Pd membrane. Long-term permeation of Pd–25Ag/V–15Ni composite membrane was carried out at 573 and 673 K for 200 h. There was no strong metallic interdiffusion between the Pd–25Ag membrane and the V–15Ni support after the long-term permeation at 573 K but small amounts of oxide had formed on the surface of Pd–25Ag membrane. Whisker and fissure-oxide morphologies were dominant on the exit and entrance side of the Pd–25Ag/V–15Ni composite membrane, respectively, accompanied by severe metallic interdiffusion after the long-term permeation at 673 K. AES and FE-SEM results revealed that metallic interdiffusion and selective oxidation of vanadium were responsible for the deterioration of Pd–25Ag membrane at 673 K. Hydrogenation–dehydrogenation of Pd and Pd–25Ag membranes supported by stainless steel and V–15Ni alloy were in situ examined by an optical microscope. The formation of hydride was uniform in the Pd/V–15Ni sample but localized in the Pd–25Ag/V–15Ni sample, suggesting that the hydrogen transfer through interface was strongly dependent on the composition of Pd alloy membranes. As for the stainless steel supported samples, both Pd and Pd–25Ag membranes had fractured.     

Nano TiO2-based preconcentration for the speciation analysis of inorganic selenium by using ion chromatography with conductivity detection

A simple, sensitive, and cost-effective analytical method was developed for the speciation analysis of inorganic selenium by combining a nano-TiO₂ preconcentration with an ion chromatography-conductivity detection (IC-CD) system. The experimental conditions for the simultaneous adsorption and desorption of Se(IV) and Se(VI) were carefully investigated. Under the established optimum condition, the Se(IV) and Se(VI) ions could been simultaneously adsorbed onto the nano-TiO₂ surface at pH 4.0, and then effectively desorbed by 0.1 M sodium hydroxide eluent. The adsorption process was fast and reached adsorption equilibrium within 10 min. The nano-TiO₂ also exhibited high adsorption capacity with 11.3 mg g^? 1 for Se(IV) and 8.34 mg g^? 1 for Se(VI). The enrichment factors for Se(IV) and Se(VI) were calculated to be 39 and 30, respectively, with sample volume of 50 mL. The detection limits (3σ) were 0.8 μg L^? 1 for Se(IV) and 0.4 μg L^? 1 for Se(VI), which were sensitive enough for the routine analysis of water and drink samples. The relative standard deviation was calculated to be < 4% (n = 6) for detection of 30 μg L^? 1 Se(IV) and 30 μg L^? 1 Se(VI). The results of the present work confirmed that our developed nano-TiO₂-IC-CD method could be applied for the detection of inorganic selenium species in tap water and drink samples with good recoveries in the range of 82%–108%.     

Photocurrent generated on a carotenoid-sensitized TiO2 nanocrystalline mesoporous electrode

Photocurrent was observed upon monochromatic illumination of an ITO electrode coated with a TiO₂ nanocrystalline mesoporous membrane with carotenoid 8′-apo-β-caroten-8′-oic acid (ACOA) deposited as a sensitizer (illuminated area 0.25 cm²) and immersed in an aqueous 10 mM hydroquinone (H₂Q), 0.1 M NaH₂PO₄ solution (pH = 7.4) purged with argon, using a platinum flag counter electrode (area 3.3 cm²) and a SCE reference electrode. The carotenoid-sensitized short-circuit photocurrent reached 4.6 μA/cm² upon a 40 μW/cm² incident light beam at 426 nm, with an IPCE (%, incident monochromatic photon-to-photocurrent conversion efficiency) as high as 34%. The short-circuit photocurrent was stable during 1 h of continuous illumination with only a 10% decrease. An open-circuit voltage of 0.15 V was obtained (upon 426 nm, 40 μW/cm² illumination) which remained at a constant value for hours. The observed open-circuit voltage is close to the theoretical value (0.22 V) expected in such a system. The action spectrum resembled the absorption spectrum of ACOA bound on the TiO₂ membrane with a maximum near 426 nm. No decay of the ACOA on the TiO₂ surface was observed after 12 h, presumably because of rapid regeneration of ACOA from ACOA⁺ at the surface by electron transfer from H₂Q.     

Developing a heating procedure to optimise hydrogen permeance through Pd–Ag membranes of thickness less than 2.2 μm

The Pd–Ag films, with a total thickness of <2.2 μm, were deposited by electroless plating on the inside of α-alumina membranes from SCT. The H₂ permeances through separated Pd–Ag layers were poor and heating conditions were investigated to improve the H₂ permeances through the metal films. The heating temperature, heating time and heating environment all had a significant effect on the H₂ permeance and the H₂ to N₂ selectivity of the Pd–Ag films. The films were oxidised at 310°C for 1 h after heat treatment in Ar at 550°C, and then reduced in H₂. This additional surface modification step more than doubled the H₂ permeance through the film and only created a moderate amount of membrane defects as indicated by the increase in the N₂ permeance. After the heating process, the membranes were characterised from 250 to 410°C using both a sweep gas and a positive pressure difference.     

Desorption related to adsorption of hydrogen via detailed balance on the Si(1 0 0) surfaces

Recent progress on desorption and adsorption dynamics of hydrogen (deuterium) on monohydride and dihydride Si(1 0 0) surfaces is reviewed and discussed. The dynamics experiments reveal that the desorption dynamics of hydrogen is well related to the adsorption dynamics via detailed balance. Dependence of time-of-flight (TOF) distributions of desorbed molecules on H(D) coverage is noticed to be important in understanding the kinetics mechanism of the adsorption/desorption reactions of hydrogen on the Si(1 0 0) surface. The desorption dynamics varies from the situation of strongly translational heating to the other situation of less translational heating with D coverage. This trend seems to be consistent with the 2H/3H/4H interdimer mechanism. However, despites by far the richest 4H configuration at high H coverage, the 2H desorption prevails over the 4H desorption already at 0.8 ML. To reconcile this unexpected desorption kinetics, a diffusion-promoted desorption mechanism is proposed. Height of the adsorption barriers for the 2H and 3H pathways could be reduced by the H-atom diffusion along the Si dimer rows, but that for the 4H pathway could not be the case because of no capability of diffusion on the H saturated surface. The desorption dynamics of hydrogen from the (3 × 1) dihydride surface is also reviewed and compared with the case on the monohydride surface. The sticking coefficients of hydrogen molecules onto the monohydride surfaces are evaluated from the TOF curves and found to be strongly activated by the kinetic energy. Not only the degrees of freedom of the molecules but also the vibrational degrees of freedom of substrate Si atoms determine the barrier height for adsorption. The desorption dynamics of hydrogen from the monohydride and dihydride surfaces appears to be quite similar, but the dynamics of substrate Si atoms is expected to be quite dissimilar between the two desorption pathways.     

Synthesis and characterization of layered zinc hydroxychlorides

Layered material of zinc hydroxychlorides (Zn₅(OH)₈Cl₂·nH₂O: ZHC), which is one of the basic zinc salts (BZS), was synthesized from ZnO nano-particles aged with aqueous ZnCl₂ solutions at different temperatures ranging from 6 to 140 °C for 48 h. X-ray diffraction (XRD) results indicated that the diffraction peaks of ZnO completely disappeared by aging at 6 °C and the ZHC peaks were developed. By increasing the aging temperature, crystallinity of the layered structure was improved. At 6 °C, the ZHC particles were thin hexagonal plate particles with sizes ranging from 1 to 3 μm. The particle size of ZHC was independent of aging temperature. The atomic Cl/Zn ratios of all the ZHC materials were almost 0.2 less than 0.4 of the theoretical ratio, indicating that the synthetic ZHC is Cl-deficient. It seemed that half of Cl atoms in the layer were replaced with HCO₃⁻ and/or OH⁻. The specific surface areas of ZHC estimated from N₂ adsorption isotherms were ca. 10 m² g⁻¹ and were independent of the aging temperature. However, the H₂O monolayer adsorption capacity per unit surface area (n_w) for all the samples was higher than that of ZnO particles, revealing the high affinity of ZHC to H₂O molecules. The n_w values were increased by reducing the crystallinity of ZHC. This enhancement of H₂O adsorption selectivity was thought to be related with less-crystallized parts of the particles.     

Correlations between hydrogen electrosorption properties and composition of Pd-noble metal alloys

Hydrogen adsorption on and absorption into Pd alloys with other noble metals was studied in acidic solutions (0.5 M H₂SO₄) using cyclic voltammetry. Correlations were found between the potentials of adsorbed/absorbed hydrogen oxidation peaks and surface/bulk compositions of Pd–Rh alloys. The potential of the α–β-phase transition depends linearly on Pd bulk content in Pd–Au, Pd–Rh, Pd–Pt and Pd–Pt–Rh alloys. The obtained relationships can be utilized for the determination of the composition of homogeneous Pd-noble alloys from hydrogen electrosorption experiments.     

Partial oxidation of ethane to syngas in an oxygen-permeable membrane reactor

A perovskite-type oxide of Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCFO) with mixed electronic and oxygen ionic conductivity at high temperatures was used as an oxygen-permeable membrane. A tubular membrane of BSCFO made by extrusion method has been used in the membrane reactor to exclusively transport oxygen for the partial oxidation of ethane (POE) to syngas with catalyst of LiLaNiO/γ-Al₂O₃ at temperatures of 800–900 °C. After only 30 min POE reaction in the membrane reactor, the oxygen permeation flux reached at 8.2 ml cm⁻² min⁻¹. After that, the oxygen permeation flux increased slowly and it took 12 h to reach at 11.0 ml cm⁻² min⁻¹. SEM and EDS analysis showed that Sr and Ba segregations occurred on the used membrane surface exposed to air while Co slightly enriched on the membrane surface exposed to ethane. The oxygen permeation flux increased with increasing of concentration of C₂H₆, which was attributed to increasing of the driving force resulting from the more reducing conditions produced with an increase of concentration of C₂H₆ in the feed gas. The tubular membrane reactor was successfully operated for POE reaction at 875 °C for more than 100 h without failure, with ethane conversion of ∼100%, CO selectivity of >91% and oxygen permeation fluxes of 10–11 ml cm⁻² min⁻¹.     

Dimeric and monomeric palladium(II) parent-amido (NH2) complexes: Synthesis,characterization, and reactivity

The treatment of [PdL₃(NH₃)]OTf (L₃ = (PEt₃)₂(Ph) (1), (2,6-(Cy₂PCH₂)₂C₆H₃) (3)) with NaNH₂ in THF afforded dimeric and monomeric parent-amido palladium(II) complexes with bridging and terminal NH₂, respectively, anti-[Pd(PEt₃)(Ph)(μ-NH₂)]₂ (2) and Pd(2,6-(Cy₂PCH₂)₂C₆H₃)(NH₂) (4). The dimeric complex 2 crystallizes in the space group P2₁/n with a = 13.228(2) Å, b = 18.132(2) Å, c = 24.745(2) Å, β = 101.41(1)°, and Z = 4. It has been found that there are two crystallographically independent molecules with Pd(1)–Pd(2) and Pd(3)–Pd(4) distances of 2.9594 (10) and 2.9401(9) Å, respectively. The monomeric amido complex 4 protonates from trace amounts of water to give the cationic ammine species [Pd(2,6-(Cy₂PCH₂)₂C₆H₃)(NH₃)]⁺. Complex 4 reacts with diphenyliodonium triflate ([Ph₂I]OTf) to give aniline complex [Pd(2,6-(Cy₂PCH₂)₂C₆H₃)(NH₂Ph)]OTf (5). Reaction of 4 with dialkyl acetylenedicarboxylate (DMAD, DEAD) yields diastereospecific palladium(II) vinyl derivative (Z)–(Pd(Cy₂PCH₂)₂C₆H₃)(CR = CR(NH₂)) (R = CO₂Me (6a), CO₂Et (6b)). Reacting complexes 6a and 6b with p-nitrophenol produces (Pd(Cy₂PCH₂)₂C₆H₃)(OC₆H₄–p-NO₂) (8) and cis-CHR = CR(NH₂), exclusively.     

Highly selective solid-phase extraction of trace Pd(II) by murexide functionalized halloysite nanotubes

The originality on the high efficiency of murexide modified halloysite nanotubes as a new adsorbent of solid phase extraction has been reported to preconcentrate and separate Pd(II) in solution samples. The new adsorbent was confirmed by Fourier transformed infrared spectra, X-ray diffraction, scanning electron microscope, transmission electron microscope and N₂ adsorption–desorption isotherms. Effective preconcentration conditions of analyte were examined using column procedures prior to detection by inductively coupled plasma-optical emission spectrometry (ICP-OES). The effects of pH, the amount of adsorbent, the sample flow rate and volume, the elution condition and the interfering ions were optimized in detail. Under the optimized conditions, Pd(II) could be retained on the column at pH 1.0 and quantitatively eluted by 2.5 mL of 0.01 mol L^?1 HCl–3% thiourea solution at a flow rate of 2.0 mL min^?1. The analysis time was 5 min. An enrichment factor of 120 was accomplished. Common interfering ions did not interfere in both separation and determination. The maximum adsorption capacity of the adsorbent at optimum conditions was found to be 42.86 mg g^?1 for Pd(II).The detection limit (3σ) of the method was 0.29 ng mL^?1, and the relative standard deviation (RSD) was 3.1% (n = 11). The method was validated using certified reference material, and has been applied for the determination of trace Pd(II) in actual samples with satisfactory results.     

Hydrogen absorption by a palladium electrode from a protic ionic liquid at temperatures exceeding 100 °C

Hydrogen adsorption in a palladium electrode driven by the electrochemical reduction of protons from a protic ionic liquid is presented. The amounts of hydrogen absorbed and desorbed in thin Pd films is similar in both the diethylmethylammonium-trifluoromethanesulfonate ionic liquid and in an aqueous H₂SO₄ solution, reaching H/Pd atomic ratios of 0.7 to 0.8. The electrochemical quartz crystal microbalance technique showed decreased absorption and desorption rates due to the slower proton transfer between the protic ionic liquid and the electrode. The use of this thermally stable ionic liquid allowed absorbing and desorbing hydrogen at temperatures up to 125 °C, increasing the rate of the reactions.     

Non-enzymatic detection of hydrogen peroxide using a functionalized three-dimensional graphene electrode

A novel three-dimensional (3D) electrochemical sensor was developed for highly sensitive detection of hydrogen peroxide (H₂O₂). Monolithic and macroporous graphene foam grown by chemical vapor deposition (CVD) served as the electrode scaffold. Using in-situ polymerized polydopamine as the linker, the 3D electrode was functionalized with thionine molecules which can efficiently mediate the reduction of H₂O₂ at close proximity to the electrode surface. Such stable non-enzymatic sensor is able to detect H₂O₂ with a wide linear range (0.4 to 660 μM), high sensitivity (169.7 μA mM^− 1), low detection limit (80 nM), and fast response (reaching 95% of the steady current within 3 s). Furthermore, this sensor was used for real-time detection of dynamic release of H₂O₂ from live cancer cells in response to a pro-inflammatory stimulant.