Pure Palladium Research Articles

Preparation of PdNi bimetallic loaded amino modified porous carbon material catalyst based on chitosan and its applications

The utilization efficiency of palladium-based catalysts has sharply increased in many catalytic reactions. However, numerous studies have shown that preparing alloys of palladium with other metals has superior catalytic activity than pure palladium. Additionally, hierarchical porous carbon has gradually developed into an excellent carrier for loading bimetallic nanoparticles. In this study, we firstly pyrolyzed chitosan, sodium bicarbonate and nickel nitrate to create highly dispersed porous carbon materials doped with Ni NPs. The carbon materials were then grafted with silane coupling agent (APTMS) to afford them with amino groups on the surface. Taking advantage of the fact that Pd2+ can react with Ni in spontaneous reduction reaction, Pd was deposited on the surface of Ni to produce PdNi bimetallic-loaded carbon catalysts containing amino groups. The resulting catalysts were examined by a series of characterizations and were found to have a hierarchically porous structure and large specific surface area, which increased the number of active sites of the catalysts. In comparison to other Pd catalysts, the PdNi/HPCS-NH2 catalysts displayed remarkable activity for Suzuki coupling reaction and hydro reduction of nitroaromatics, which exhibited a high turnover frequency value (TOF) of 37,857 h−1 and 680.9 h−1, respectively. These were mainly due to the high dispersion of the PdNi NPs and the superior structure of the carriers. Moreover, the catalysts did not experience a significant decline in activity after ten cycles. All in all, this investigation has created a new approach for the fabrication of novel carriers for Pd catalysts, which is in line with the concept of green chemistry and recyclable.

Fabrication of Microporous Palladium by Selective Anodic Dissolution of Ag-Pd Alloy in Alkali Chlorides Melt

The electrochemical dealloying of Ag40Pd60 alloy in (LiCl)57(CsCl)26(KCl)17 melt with the addition of 3 mol% silver chloride has been studied. Selective anodic dissolution of the alloy was carried out both in the potentiostatic and in galvanostatic regimes at temperatures ranging from 300 to 500 °C. The obtained voltammetry characteristics of the initial alloy, chronoamperograms and chronopotentiogram during the dealloying are presented and discussed. At a temperature near 500 °C, the second maximum was observed in the chronoamperograms at two different values of the set potential. The unusual shape of the current curves is due to the superposition of several diffusion processes, which intensities in this case are greater than at lower temperatures. Bi-continuous structures of practically pure palladium with pores and ligaments of sizes ranging from a few to tens of micrometers were obtained in the potentiostatic regime. As the dealloying temperature increased, the sizes of pores and ligaments increased naturally. The same effect was also caused by the increase in applied potential. In the galvanostatic mode similar metallic structures were obtained, but the residual silver content reached 5%, and, in addition, the effects of samples sintering appeared.

ПЕРСПЕКТИВИ РОЗВИТКУ ВОДНЕВОЇ ЕНЕРГЕТИКИ З МОЖЛИВІСТЮ ВІДНОВЛЕННЯ МЕМБРАН ДЛЯ ПАЛИВНИХ ЕЛЕМЕНТІВ ПІСЛЯ КОНТАКТУ З ВОДНЕМ

The prospects for the development of hydrogen energy and the influence of temperature on the change in the shape of the membrane for fuel cells in contact with hydrogen have been studied. It has been confirmed that the change in the shape of the plate from the α-PdHn gradient alloy develops in two stages. The experimental regularities of the change in the shape of the palladium membrane during operation in a hydrogen environment were investigated. It was determined that upon contact with hydrogen, a temporary gradient material "metal-hydrogen" is formed in the membrane, which causes the development of hydrogen concentration stresses, and the maximum change in the shape of the membrane, which occurs at a constant temperature, depends on the diffusion coefficient and the equilibrium solubility of hydrogen in palladium. However, when the temperature changes, the diffusion coefficient of hydrogen in palladium and the equilibrium concentration of hydrogen in palladium also change, which affects the temperature dependence of the final shape change of the membrane. This fact makes it possible to effectively plan and determine the time of hydrogen penetration into the membrane, control the change of shape and adjust the operating modes of the fuel cell. It is the equilibrium solubility of hydrogen in palladium and its diffusion coefficient when the temperature changes in the main that determine the maximum and final change in the shape of the membrane, and the temperature determines the fluctuation of the change in the shape of the membrane when the temperature of the hydrogen flow entering the chamber changes. Thus, the complete return of the membrane to its initial state at increased temperature clearly indicates the implementation of a coherent membrane bending mechanism. Upon completion of hydrogen saturation by the coherent mechanism under the conditions of reaching equilibrium with the gas phase, the original palladium membrane turns out to be transformed into a membrane of the equilibrium alloy α-PdHnо, which inherits the initial state of a pure palladium membrane. Therefore, to model the hydrogen penetration process in the fuel cell, it is necessary to know the gas flow rate, membrane permeability and gas temperature, as well as the diagram of the fuel cell where these processes take place. At the same time, scientists still hope for the future development of hydrogen energy, despite the existing difficulties. This requires additional research and development of new technologies to remove obstacles to the transition to hydrogen as a primary energy source

Determination of change in enthalpy and entropy for hydride formation and decomposition of palladium using in-situ electrical resistance measurement with various hydrogen pressures

Detection of hydride formation and decomposition of palladium is performed on pure palladium in the hydrogen gas atmosphere up to 0.5 MPa between room temperature and 673 K using an in-situ electrical resistance measurement system. Introduction of hydrogen gas increases the electrical resistance about 1.1 time higher than that in vacuum. Electrical ratio-temperature plot gives a peak during heating and cooling with the temperature changing ration of 0.067 K/s under hydrogen gas, which are associated with the hydride composition and decomposition. Change in enthalpy ΔH and entropy ΔS are determined using van't Hoff plot, and the values were comparable to the reported ones obtained by pressure-composition-temperature measurements. Those for hydride decomposition are 45.6±2.6 (kJ/mol) and 104.8±5.3 (J/mol), respectively, and those for hydride formation are -29.4±2.1 (kJ/mol) and 73.8±4.6 (J/mol), respectively. Furthermore, the measurement method is relatively simple and easy compared with pressure-composition-temperature measurements.

H2 permeance and surface characterization of a thin (2 μm) Pd-Ni composite membrane prepared by electroless plating

The high cost of palladium membranes limits their widespread use in industrial applications. We report a novel strategy for the preparation of economic hydrogen separation membranes. In this study, a Pd88-Ni12 composite membrane was prepared with a considerable nickel content (>10 wt%) for the first time using the organic–inorganic activation method in the ELP approach. The H2 permeance of the Pd88-Ni12 composite membrane was 4.34 × 10-7 mol m−2 s−1 Pa−1 at 500 °C with infinite selectivity (H2/N2). The membrane exhibited suitable performance when exposed to binary mixtures under various operating conditions. At 500 °C and 100 kPa, with the same concentration of impurity gases, the H2 permeance of the Pd88-Ni12 composite membrane was 3.33 × 10 -7 mol m−2 s−1 Pa−1 for the H2-Ar mixture, 3.12 × 10 -7 mol m−2 s−1 Pa−1 for the H2-N2 mixture, 2.56 × 10 -7 mol m−2 s−1 Pa−1 for the H2-CO2 mixture, and 2.54 × 10 -7 mol m−2 s−1 Pa−1 for the H2-CO mixture. The effect of operating parameters and the amount of impurity concentration in the gas feed on the stage cut in binary gas mixtures was investigated. Increasing operating temperature and pressure enhanced the stage cut for all mixtures while increasing the impurity concentration in the gas feed led to a decrease in the stage cut, independent of operating conditions. The Pd88-Ni12 composite membrane indicated suitable long-time permeance stability for 150 h at a transmembrane pressure range of 100–300 kPa and 500 °C under an H2/N2 gas atmosphere. Finally, the cost investigation demonstrated that the Pd88-Ni12 composite membrane had a 38 % lower specific cost than the pure palladium composite membrane.

Thermodynamics and kinetics hydrogen isotope effects of hydrogen/deuterium absorption in Pd-5wt.%Pt alloy

Palladium–Platinum (Pd–Pt) alloys have excellent hydrogen isotope separation properties near room temperature compared to pure palladium (Pd), and are expected to be used as filling materials in thermal cyclic absorption (TCAP) columns. However, most studies on the thermodynamic and kinetic hydrogen isotope effects of hydrogen absorption/deuterium in Pd–Pt alloys have been conducted at temperatures of 273 K or above, with few studies involving the performance of TCAP in the cold-cycle operating temperature range (253 K–303 K). In this work, the performance of Pd-5wt.%Pt alloy for the absorption of hydrogen/deuterium at low temperatures (263 K–323 K) was investigated. The results show that the enthalpy and entropy of dissolution of hydrogen and deuterium in the α-phase of Pd-5wt.%Pt alloy are −11.77 kJ/mol (H), 104.00 J mol−1 K−1(H); −5.50 kJ/mol (D), 87.88 J mol−1 K−1 (D), respectively, which are lower than the enthalpy and entropy change values of pure Pd materials. The apparent reaction activation energies of protium and deuterium absorption are −4.14 kJ/mol (H2) and −11.87 kJ/mol (D2), respectively, which are lower than those of pure palladium. The excellent hydrogen isotope separation performance of Pd–Pt alloys may originate from the fast hydrogen absorption and discharge isotope kinetic performance.

Hydrogen Permeability of Composite Pd-Au/Pd-Cu Membranes and Methods for Their Preparation.

Thin Pd-40%Cu films were obtained via the classical melting and rolling method, magnetron sputtering, and modified with nanostructured functional coatings to intensify the process of hydrogen transportation. The films were modified by electrodeposition, according to the classical method of obtaining palladium black and "Pd-Au nanoflowers" with spherical and pentagonal particles, respectively. The experiment results demonstrated the highest catalytic activity (89.47 mA cm-2), good resistance to CO poisoning and long-term stability of Pd-40%Cu films with a pentagonal structured coating. The investigation of the developed membranes in the hydrogen transport processes in the temperature range of 25-300 °C also demonstrated high and stable fluxes of up to 475.28 mmol s-1 m-2 (deposited membranes) and 59.41 mmol s-1 m-2 (dense metal membranes), which were up to 1.5 higher, compared with membrane materials with classic niello. For all-metal modified membranes, the increase in flux was up to sevenfold, compared with a smooth membrane made of pure palladium, and for deposited films, this difference was manyfold. The membrane materials' selectivity was also high, up to 4419. The developed strategy for modifying membrane materials with functional coatings of a fundamentally new complex geometry can shed new light on the development and fabrication of durable and highly selective palladium-based membranes for gas steam reformers.

A Case Study Approach: Summary of Some Results on the Effects of Hydrogen Exposure on the Mechanical Properties of Palladium and the Alloy Systems Pd1−xMx, M = Ag, Cu, Mn; x = 5 − 0.25

Selected results of investigations focused on the changes to some mechanical properties of palladium and several palladium-based alloys caused by exposure to hydrogen have been collected and presented. The findings indicate that the mechanical properties of pure palladium are highly susceptible to alteration upon exposure to hydrogen. In the cases of alloying palladium with silver and copper, the alloys, as compared to palladium, appear to resist changes to mechanical properties. In the case of alloying palladium with manganese, the interesting order–disorder phenomenon plays an important role on the effects of hydrogen exposure on their mechanical properties.

Phase Transformation during the Selective Dissolution of a Cu85Pd15 Alloy: Nucleation Kinetics and Contribution to Electrocatalytic Activity

This study determined the critical parameters for the morphological development of the electrode surface (the critical potential and the critical charge) during anodic selective dissolution of a Cu-Pd alloy with a volume concentration of 15 at.% palladium. When the critical values were exceeded, a phase transition occurred with the formation of palladium's own phase. Chronoamperometry aided in the determination of the partial rates of copper ionization and phase transformation of palladium under overcritical selective dissolution conditions. The study determined that the formation of a new palladium phase is controlled by a surface diffusion of the ad-atom to the growing three-dimensional nucleus under instantaneous activation of the nucleation centres. We also identified the role of this process in the formation of the electrocatalytic activity of the anodically modified alloy during electro-oxidation of formic acid. This study demonstrated that HCOOH is only oxidated at a relatively high rate on the surface of the Cu85Pd15 alloy, which is subjected to selective dissolution under overcritical conditions. This can be explained by the fact that during selective dissolution of the alloy, a pure palladium phase is formed on its highly developed surface which has prominent catalytic activity towards the electro-oxidation of formic acid. The rate of electro-oxidation of HCOOH on the surface of the anodically modified alloy increased with the growth of the potential and the charge of selective dissolution, which can be used to obtain an electrode palladium electrocatalyst with a set level of electrocatalytic activity towards the anodic oxidation of formic acid.

Recovery of palladium using 1-cyanopropyl-3-methylimidazolium chloride based aqueous biphasic system combined with electrodeposition

Liquid-liquid extraction (LLE) is one of the most widely used strategies of recover elemental metals, but normally requires a large quantity of organic solvents. To develop a more environmental friendly method, we have developed a novel approach for palladium (Pd) recovery, which requires only the ionic liquid 1-cyanopyl-3-methylimidazolium chloride ([C3CNmim][Cl]) and potassium phosphate (K3PO4). A [C3CNmim][Cl]-based aqueous biphasic system was used for Pd extraction, followed by an electrodeposition directly into the extracted phase. The results indicated that the extraction percentage could be as high as 100% with 5% [C3CNmim][Cl] + 60% K3PO4 at a Pd(II) concentration of 10 mg/L ∼25 mg/L. Pure palladium was obtained after electrodeposition followed by calcination. The nitrile group enhanced the coordination to Pd, but did not significantly affect the electrochemical window. It is expected that Pd can be recovered on an industrial scale using this protocol.

Recovery of Palladium Metal with High Purity by Selective Reduction from Inorganic Acid Leaching Solutions of Cemented Zinc

A small amount of Pd(II) present in spent electroplating solutions is concentrated by cementation. In this work, a process was developed to recover pure palladium metal by selective reduction from the hydrochloric and the sulfuric acid leaching solutions of cemented zinc. For this purpose, hydrazine and ascorbic acid were employed as reducing agents and the effect of several variables such as the acidity of the leaching solutions, molar ratio of reducing agents to Pd(II), reaction time and temperature was investigated. Since neither of the reducing agents can reduce Pd(II) from strong acidic solutions, it was necessary to decrease the acidity of the leaching solutions by dilution with distilled water. Our results indicated that it was possible to recover Pd metal with high purity by selective reduction after diluting the hydrochloric and sulfuric acid leaching solutions of cemented zinc with distilled water. When the molar ratios of the reducing agents to Pd(II) were the same, the reduction percentage of Pd(II) from the sulfuric acid solution was higher than that from the hydrochloric acid solution, due to the much higher complex formation constant of PdCl42- than Pd(SO4)22-. The reduction of Pd(II) by hydrazine occurred within 15 mins at room temperature, while a higher temperature (60 oC) and longer reaction time (1h) were necessary to reduce Pd(II) with ascorbic acid. The reduction of Pd(II) from sulfuric acid solution was more efficient than from hydrochloric acid solution. It was possible to recover Pd metal with high purity from the leaching solution of cemented zinc using the reduction method.

Palladium nanosheets bunches for stable and high-concentration hydrogen sensing at room temperature

Pure palladium (Pd) and Pd alloy for hydrogen (H2) sensing is widely studied for detecting the high-concentration H2 leakage (e.g., 4–30 v/v%), such as in those applications of aerospace crafts and hydrogen-driven vehicles, which may suffer from the saturation of adsorbing H2, leading to instability at room temperature. To address the above issue, the ultrathin Pd nanosheets bunches (NSTs-BCHs) have been developed for the stable detection of high-concentration H2 at room temperature. With a wet-chemical synthesis, the CO released from the thermal decomposition of metal-carbonyl compounds assists in forming Pd-based NSTs-BCHs (2–5 nm thick). The Pd-based NSTs-BCHs without dopants show unstable and saturated response towards H2 with a concentration>3 v/v%. Comparatively, the ones with W dopants display excellent sensing stability towards a wide concentration range of 100 ppm − 30 v/v% H2. Theoretically, the large specific surface and the W dopants in Pd-based NSTs-BCHs are believed to contribute to stable detection of high-concentration H2, which may be applied to other sensing materials for high-concentration gas detection.

Analysis of hydrogen embrittlement in palladium–copper alloys membrane from first principal method using density functional theory

Hydrogen embrittlement has significant effects on membrane properties, and it is vital to develop countermeasures to avoid this problem from the start. The impact of hydrogen on pure palladium and palladium-copper alloys used for hydrogen purification/separation was investigated in this study. It was discovered that the lattice parameter and crystalline structure of pure Pd change from 3.92 Å to 5.55 Å and from cubic structure to triclinic structure, respectively. The presence of hydrogen atoms in the crystalline structure is responsible for this alteration. The absorption enthalpy of Pure Pd and PdCu of −4.38eV and −4.86eV, respectively, showed that a PdCu membrane with a lower enthalpy value increased anti-hydrogen brittleness. Due to hydrogen exposure, the mechanical characteristics of pure palladium were considerably affected. This study demonstrates that the mean peak on EF of Pd–Cu (0.259eV) is lower than that of pure Pd (0.955eV) when exposed to hydrogen, indicating more stability and lower hydrogen embrittlement in Pd–Cu alloy than pure Pd. Density functional theory-based simulation is used to analyse what happened at the grain boundary, the causes of hydrogen embrittlement, and possible ways to prevent it.

Effect of Ethylene Glycol on the Dissolution of Palladium with HCl Solution Containing Oxidizing Agents and Selective Precipitation of Pd(IV) Compound

There is growing interest in the recovery of pure palladium (Pd) compound from cemented Pd from spent electroplating solutions due to increasing demand for Pd, and there is considerable motivation to develop an efficient recovery process. In conventional methods of leaching Pd metal, HCl solutions containing oxidizing agents are employed. In this work, ethylene glycol (EG) replaced water as a diluent in the HCl solution containing oxidizing agents such as H2O2, NaClO and NaClO3. Leaching of the Pd metal and the subsequent precipitation of the Pd(IV) compound was investigated. Among the three kinds of oxidizing agent, NaClO3 showed the best Pd metal leaching efficiency from a metallic mixture of Pd and Zn from HCl in EG solution. The role of EG in enhancing the leaching and precipitation is discussed in light of its interaction with other components in the solutions. To precipitate the Pd(IV) compound with NH4Cl, it is important that the dissolved Pd ion exists as Pd(IV). Therefore, NaClO3 was again added to the leaching solution to verify the oxidation of Pd(II) to Pd(IV). Extra pure ammonium hexachloropalladate ((NH4)2PdCl6) was recovered by precipitation from the leaching solution of the cemented Pd under the optimum conditions. Compared to conventional HCl systems, the present process shows some advantages, by reducing both chemical dosage and energy consumption. The results confirm a process can be developed for the recovery of the Pd(IV) compound from spent electroplating solutions containing a small amount of Pd(II).

Electrochemical corrosion of multiphase stainless steel-based alloy nuclear waste forms

The electrochemical corrosion behaviors of two multiphase alloys representing waste forms made with 316 L stainless steel and different amounts of surrogate metallic fuel wastes were measured and related to the microstructures. Potentiodynamic (PD) scans were performed in an acid brine solution and the corroded surfaces were characterized with scanning electron microscopy (SEM) to compare the electrochemical responses to the corrosion of specific phases. PD scans for the two multiphase alloys, 316 L stainless steel, and pure palladium were compared to understand the complex corrosion behavior of these multiphase alloys also recently classified as multi principle element alloys (MPEAs) and to determine the effects of alloying elements and noble metals present in constituent phases on the corrosion behavior.

Separation of Pd(II) and Zn(II) from Sulfuric Acid Solution by Commercial Extractants

Spent electroplating solutions contain a small amount of Pd(II). This Pd(II) can be concentrated by cementation with zinc metal powder. In order to recover pure palladium, a hydrometallurgical process consisting of leaching followed by solvent extraction was developed in this work. First, suitable extractants for the selective extraction of Pd(II) over Zn(II) were selected from synthetic sulfuric acid solutions. Among cationic, solvating and basic extractants employed in this work, Cyanex 301, LIX 63 and Aliquat 336 showed selectivity for Pd(II) over Zn(II) from 5 M sulfuric acid solutions. Stripping results for the loaded phases of these three extractants showed that HCl was effective at stripping Pd(II) from the loaded LIX 63 and Aliquat 336, while a mixture of inorganic acid and NaClO as an oxidizing agent was necessary to strip Pd(II) from the loaded Cyanex 301. The cemented Pd was completely dissolved using 5 M sulfuric acid solution at 25 oC, and the concentration of Pd(II) and Zn(II) in the real leaching solution was 1.926 and 0.074 g/L, respectively. Application of the optimum conditions for the selective extraction of Pd(II) over Zn(II) to the real sulfuric acid leaching solution of cemented Pd indicated that only LIX 63 and Cyanex 301 could separate Pd(II) from Zn(II). The stripping efficiency of Pd(II) by a mixture of 5 M HCl and 3% NaClO was much higher from the loaded LIX 63 than from the loaded Cyanex 301. Considering the extraction and stripping characteristics of Pd(II), LIX 63 was selected as an optimum extractant for the separation of Pd(II) from the real sulfuric acid leaching solution of cemented Pd.

On the Potential of Gallium- and Indium-Based Liquid Metal Membranes for Hydrogen Separation.

The concept of liquid metal membranes for hydrogen separation, based on gallium or indium, was recently introduced as an alternative to conventional palladium-based membranes. The potential of this class of gas separation materials was mainly attributed to the promise of higher hydrogen diffusivity. The postulated improvements are only beneficial to the flux if diffusion through the membrane is the rate-determining step in the permeation sequence. Whilst this is a valid assumption for hydrogen transport through palladium-based membranes, the relatively low adsorption energy of hydrogen on both liquid metals suggests that other phenomena may be relevant. In the current study, a microkinetic modeling approach is used to enable simulations based on a five-step permeation mechanism. The calculation results show that for the liquid metal membranes, the flux is limited by the dissociative adsorption over a large temperature range, and that the membrane flux is expected to be orders of magnitude lower compared to the membrane flux through pure palladium membranes. Even when accounting for the lower cost of the liquid metals compared to palladium, the latter still outperforms both gallium and indium in all realistic scenarios, in part due to the practical difficulties associated with making liquid metal thin films.

Structure and properties of niobium carbide coated vanadium composite membranes for high temperature hydrogen separation

Niobium carbide (NbC) catalytic films were deposited on vanadium (V) foils by magnetron sputtering to prepare the NbC/V composite membranes for high temperature hydrogen separation. It is found that the sputtering power and substrate bias largely affect the structure and catalytic activity of the NbC films, and thus the hydrogen permeability of the NbC/V composite membranes. Optimized conditions for membrane preparation were obtained, which generated a pronounced high hydrogen permeability, particularly ~5.85 × 10−8 mol H2 m−1 s−1 Pa−0.5 at 650 °C. This is 1.9 times that of pure palladium (Pd). The high hydrogen permeability of the NbC/V membranes can be attributed to the high catalytic activity of the NbC films towards hydrogen dissociation, as the cubic NbC phase in the films exhibits preferential growth along the catalytically dominated crystalline plane and a relatively high percentage. This work demonstrates that the NbC/V system shows high potential as a new non-precious metal membrane for hydrogen separation and purification at high temperatures.

Recovery of pure palladium compound from the spent electroplating solutions by hydrometallurgical method

Recovery of pure palladium compound from the spent electroplating solutions by hydrometallurgical method

Hydrogen storage on multiple palladium-decorated graphene

The geometries, structural stability, electrical and magnetic characteristics of pure and multiple palladium (Pd)-adsorbed graphene, followed by hydrogen adsorption, are investigated using first-principles calculations with the density functional theory. In the DFT-D2 technique, first-principles computations with the van der Waals interaction are done using the generalized gradient approximation. In a [Formula: see text] supercell, the adsorption energy per Pd atom is found to be 1.20 eV in the optimal adsorption shape. The bandgap of 51 meV has opened in multiple Pd-decorated graphene, according to band calculations. This band’s opening is ascribed to a symmetry break. The binding energy for hydrogen adsorption in optimal double Pd-decorated graphene was determined to be in the range of (0.14–0.73) eV per hydrogen molecule, indicating that Pd-decorated graphene might be used as a hydrogen storage material.