Pd-Ag Alloy Research Articles

Effect of Radiofrequency Power Sputtering on Silver-Palladium Nano-coatings for Mild Steel Corrosion Protection in 3.5% NaCl Solution

Silver (Ag), palladium (Pd), and bimetallic silver-palladium (Ag-Pd) coatings were deposited on a mild steel surface by the co-sputtering method. The aim was to investigate and compare the corrosion behavior of Ag-Pd nano-coatings as well as the effect of increasing the weight ratio of Ag in the Ag-Pd alloy in the 3.5% NaCl solution. The corrosion protection performance and barrier protection properties were monitored using electrochemical impedance spectroscopy and potentiodynamic polarization. The surface of the coatings was characterized by scanning electron microscopy, atomic force microscopy, energy-dispersive x-ray spectroscopy, and field-emission scanning electron microscopy. The results of corrosion measurements revealed a relationship between silver wt.% and corrosion resistance. Also, all the coatings had protective effects and barrier properties on the mild steel in the corrosive solution. The best efficiency was observed in silver monometallic coating with 54 nm thickness.

Insight into the Structures and Electrocatalytic Activities of PdAg Alloy on RGO in the Oxidation of Ethanol, Ethylene Glycol and Glycerol

The biorenewable alcohols are identified as the promising energy in fuel cells, but the lack of efficient catalysts limits the electricity output. Here, we chemically grew the PdAg alloy nanoparticles (NPs) on reduced graphene oxide (RGO) to obtain PdxAgy(m)/RGO, and investigated the dependences of peak current densities on the metal loadings (m), Pd mole fractions (x), and sizes. The maximal peak currents of 1.86, 4.88, 14.3 and 13.6 × 104 mA cm−2 mgPd−1 were respectively achieved in the electrooxidation reactions of methanol, ethanol, ethylene glycol and glycerol. It is shown that the interactions of PdAg NPs with RGO can control the catalytic efficiencies through mediating the electronic characteristics of metal NPs and the reactant absorptions. Except the catalysts for methanol oxidation reaction, the efficient catalysis possesses the same lattice structure in PdAg alloys with the optimized m, and gives a common descriptor to select the catalyst with high catalytic activity.

Alumina-Supported Palladium–Silver Bimetallic Catalysts with Single-Atom Pd1 Sites in the Liquid-Phase Hydrogenation of Substituted Alkynes

The catalytic characteristics of Pd–Ag/Al2O3 bimetallic catalysts with an Ag/Pd atomic ratio of 0.03–3.0 have been studied in the selective liquid-phase hydrogenation of diphenylacetylene and 1-phenyl-1-propyne. It has been found that an increase in the Ag/Pd ratio leads to a significant increase in selectivity, which, however, is accompanied by a decrease in the catalyst activity. Comparison with data of an earlier structural study suggests that an increase in selectivity observed with an increase in the Ag/Pd ratio to 0.5–1.0 is attributed to the following two factors: (1) the suppression of the formation of palladium hydride and (2) an increase in the fraction of “single-atom” Pd1 sites isolated from each other by Ag atoms on the surface of the Pd–Ag nanoparticles. An increase in the Ag/Pd value to 2.0–3.0 leads to a further increase in the selectivity, which exceeds the selectivity of a commercial Lindlar catalyst (Pd–Pb/CaCO3). In this case, the most probable cause of the high selectivity is the formation of the single-atom Pd1 sites on the surface of the Pd–Ag alloy and an increase in the stability of the structure.

Flux-Reducing Tendency of Pd-Based Membranes Employed in Butane Dehydrogenation Processes.

We report on the effect of butane and butylene on hydrogen permeation through thin state-of-the-art Pd–Ag alloy membranes. A wide range of operating conditions, such as temperature (200–450 °C) and H2/butylene (or butane) ratio (0.5–3), on the flux-reducing tendency were investigated. In addition, the behavior of membrane performance during prolonged exposure to butylene was evaluated. In the presence of butane, the flux-reducing tendency was found to be limited up to the maximum temperature investigated, 450 °C. Compared to butane, the flux-reducing tendency in the presence of butylene was severe. At 400 °C and 20% butylene, the flux decreases by ~85% after 3 h of exposure but depends on temperature and the H2/butylene ratio. In terms of operating temperature, an optimal performance was found at 250–300 °C with respect to obtaining the highest absolute hydrogen flux in the presence of butylene. At lower temperatures, the competitive adsorption of butylene over hydrogen accounts for a large initial flux penalty.

PdAg alloy nanoparticles encapsulated in N-doped microporous hollow carbon spheres for hydrogenation of CO2 to formate

Here, we report a general synthesis approach to produce PdAg nanoparticles (NPs) that are dispersed uniformly within N-doped microporous hollow carbon spheres (NMHCS) for hydrogenation of CO2 to formate. The optimized PdAg@NMHCS catalyst, which was obtained by using an optimized amount of ethylenediamine as the nitrogen source and pyrolyzed at 500 °C, exhibits extraordinary activity for CO2 hydrogenation to formate, showing a high turnover number (TON) of 640 and 2750 at 100 °C after 2 and 24 h, respectively. Experiments reveal that different carbonization temperatures cause changes in the surface area, the nitrogen content of NMHCS, PdAg NPs dispersion, and the formation of Pd-N bonds. Upon consideration of kinetic analyses, N-doped MHCS are not only effective for the adsorption of CO2 due to the doping of nitrogen but also would reduce the activation energy barrier for CO2 hydrogenation to formate by facilitating including CO2 adsorption/insertion step and H2 dissociation step.

Ag–Pd Alloy Immobilized on Semi-heterogeneous Support as a Novel Highly Efficient Artificial Nitroreductase: Experimental Design Optimization and Kinetic Study

The bimetallic nanocatalysts with improved catalytic activity and selectivity has emerged as an important class of nanocatalysts. Herein, a highly efficient Ag–Pd alloy-based semi heterogeneous magnetic nanocatalyst has been developed. The catalyst exhibits enzyme-like catalytic efficiency for the reduction of nitro functional group of 4-nitro phenol as water contaminant by NaBH4 even at ambient temperature. Exceptionally high turnover frequency, very short reaction time, simple recovery and reusability of catalyst and complete conversion of p-nitrophenol are some remarkable features of this semi heterogeneous nanocatalyst. The enzyme-like efficiency of developed nanocatalyst could be related to its architectural configuration, the catalytic performance of Ag–Pd bimetallic alloy nanoparticles and organophilic microenvironment which raised from semi heterogeneous nature of support. Moreover, the design of experiments methodology was employed to optimize the reaction conditions and the kinetic study was carried out to explore enzyme-like activity of designed catalyst. A novel Ag–Pd alloy-based semi heterogeneous magnetic nanocatalyst represented superior catalytic activity and selectivity for the reduction of p-nitrophenol in water even at room temperature.

Asymmetric Au/(PdAg alloy) nano-allium giganteums for their enhanced electrocatalytic performances to ethanol oxidation reaction

Morphology control is an effective strategy to enhance the electrocatalytic of metal nanocrystals in fuel cells. Herein, we synthesized Au/(PdAg alloy) nano-allium giganteums with a very high purity of almost 99% using an easy operation synthetic method. The Au/(PdAg alloy) nano-allium giganteum, in which PdAg alloyed nanoparticles only located on one end of the Au NR, was successfully obtained through a Ostwald ripening process which is significantly promoted by the addition of Br− ions. Due to the alloyed feature and the special morphology, we also utilized the Au/(PdAg alloy) nanostructures as electrocatalysts toward the ethanol oxidation reaction in alkaline and benchmarked to the commercial Pd/C nanoparticles. The specific activity of Au/(PdAg alloy) nano-allium giganteum is 2.1 mA cm−2, which is 3.2 times of the commercial Pd/C (0.65 mA cm−2). The Au/(PdAg alloy) electrocatalysts also have a higher mass activity of 0.73 A mg−1Pd, which is 2.0 times that of commercial Pd/C (0.36 A mg−1Pd). Furthermore, the durability is also highly improved due to the presence of the exposed Au NR. We thus believed that the Au/(PdAg alloy) nano-allium giganteums can become an attractive catalyst in fuel cells.

One-pot synthesis of alloyed PdAg networks as efficient catalysts of ethylene glycol electro-oxidation in alkaline media

It is of great significance to develop a simple, cheap, and efficient catalyst preparation method for the development of fuel cells. Despite considerable developmental efforts have been substantial, progress has been underwhelming. To this end, a simple one-pot approach has been designed for the fabrication of Pd–Ag alloy networks (NWs) catalysts using sodium borohydride (NaBH4) as the reducing agent and cetyltrimethylammonium bromide (CTAB) as the surfactant. The electrochemical results reveal that the addition of Ag not only reduces Pd consumption but also enhances the catalytic properties of the electrocatalysts. Particularly, the current density of a Pd2Ag1 NWs-catalyzed ethylene glycol electro-oxidation reaches 1902.9 mA mg−1, which is 1.40 times higher than that for commercial Pd/C. The catalyst’s impressive performance could be attributed to its distinctive network-like structure and the promoting effect of Ag, which is in agreement with the bi-functional mechanism and a d-band electronic structure. This work is expected to have an impact for optimization of the design of high-performance Pd-based catalysts for applications in fuel cells and in the related fields.

Boosting formic acid dehydrogenation via the design of a Z-scheme heterojunction photocatalyst: The case of graphitic carbon nitride/Ag/Ag3PO4-AgPd quaternary nanocomposites

The development of an efficient, eco-friendly, practical, and selective way to decompose formic acid (FA) into H2 and CO2 is crucial for the utilization of FA as a chemical hydrogen storage material in hydrogen economy. In this regard, photocatalytic FA dehydrogenation attracts great attention owing to its potential to meet the above-mentioned requirements. Interestingly, there is no example of heterojunction photocatalyst that tunes the hole potential of the semiconductor, resulted in a better photocatalytic activity. We report herein for the first time the design and fabrication of a novel Z-scheme heterojunction photocatalyst for FA dehydrogenation, denoted as g-CN/Ag/Ag3PO4-AgPd comprising graphitic carbon nitride (g-CN) and Ag3PO4 semiconductors, Ag and AgPd alloy nanoparticles (NPs). The designed g-CN/Ag/Ag3PO4-AgPd photocatalysts boosted the FA dehydrogenation by creating more positive hole potential and improving the charge separation efficiency of the two distinct semiconductors. The g-CN/Ag/Ag3PO4-AgPd photocatalysts provided a very high turnover frequency (TOF) of 2107 h−1 in the FA dehydrogenation under white-LED illumination at 50 °C. This TOF is 3.2 times and 44 times greater than those of g-CN/AgPd and g-CN/Pd binary non-Z-scheme heterojunction catalysts, respectively, under the same conditions and comparable to the best photocatalysts and heterogeneous catalysts reported in the FA dehydrogenation so far.

Sustainable solid-state synthesis of uniformly distributed PdAg alloy nanoparticles for electrocatalytic hydrogen oxidation and evolution

New sustainable syntheses based on solid-state strategies have sparked enormous attention and provided novel routes for the synthesis of supported metallic alloy nanocatalysts (SMACs). Despite considerable recent progress in this field, most of the developed methods suffer from either complex operations or poorly controlled morphology, which seriously limits their practical applications. Here, we have developed a sustainable strategy for the synthesis of PdAg alloy nanoparticles (NPs) with an ultrafine size and good dispersion on various carbon matrices by directly grinding the precursors in an agate mortar at room temperature. Interestingly, no solvents or organic reagents are used in the synthesis procedure. This simple and green synthesis procedure provides alloy NPs with clean surfaces and thus an abundance of accessible active sites. Based on the combination of this property and the synergistic and alloy effects between Pd and Ag atoms, which endow the NPs with high intrinsic activity, the PdAg/C samples exhibit excellent activities as electrocatalysts for both the hydrogen oxidation and evolution reactions (HOR and HER) in a basic medium. Pd9Ag1/C showed the highest activity in the HOR with the largest j0,m value of 26.5 A g Pd−1 and j0,s value of 0.033 mA cmPd−2, as well as in the HER, with the lowest overpotential of 68 mV at 10 mA cm−2. As this synthetic method can be easily adapted to other systems, the present scalable solid-state strategy may open opportunity for the general synthesis of a wide range of well-defined SMACs for diverse applications.

Chemical Hydrogen Storage and Release Driven by PdAg Alloy Nanoparticle Catalysts

Chemical Hydrogen Storage and Release Driven by PdAg Alloy Nanoparticle Catalysts

Preparation and Characterization of Spherical AgPd Alloy Powder through Wet Chemical Reduction Method

Preparation and Characterization of Spherical AgPd Alloy Powder through Wet Chemical Reduction Method

Controlled synthesis and characterization of AgPd nanowire arrays for electrocatalytic applications

Abstract Polycrystalline AgPd alloy nanowires were synthesized by potentiostatic electrodeposition in pores of anodic alumina oxide membranes from a bath containing ammonia complexes of silver and palladium. By adjusting the potential of the working electrode in a range from −0.4 to −1.2 V vs. SCE and electrolyte composition (Pd/Ag precursor ratio of 1:15 to 15:1), the morphology and composition of nanowires, and pore-filling rate can be tuned. Smooth nanowires (composed mainly of palladium) with the diameter of 56 ± 4 nm were prepared by electrodeposition carried out at the potentials less negative than −0.6 V vs. SCE in the electrolyte with the Pd/Ag precursor ratio of 15:1. The use of bath with the Pd/Ag precursor ratio of 1:15 led to the formation of rougher nanowires with a higher silver content (up to 100 wt%) and smaller diameter, which are prone to cracking due to their granular structure. The AgPd nanowire array with the Ag/Pd ratio (wt%) of ca. 1:1 was used for electrocatalytic reduction of trichloromethane in a 0.05 M aqueous solution of KClO4. The linear sweep voltammetry (LSV) revealed one wide peak of CHCl3 reduction that is shifted toward more negative values with increasing the scan rate.

PdAg Alloy Nanocatalysts: Toward Economically Viable Nitrite Reduction in Drinking Water

Nitrite (NO2–) is the primary reduction product of nitrate (NO3–), which is the most predominant contaminant in global freshwater. Both species present major environmental challenges; NO2– is also ...

Analysis for Reverse Temperature Dependence of Hydrogen Permeability through Pd-X (X = Y, Ho, Ni) Alloy Membranes Based on Hydrogen Chemical Potential.

It is generally understood that the hydrogen permeability of Pd-Ag alloy membranes declines with decreasing temperature. However, recent studies have revealed that the hydrogen permeability of Pd-Ag alloy membranes inversely increases at a certain temperature range and reaches a peak. The peak behavior reflects the shape of pressure-composition isotherms (PCT curves). In order to elucidate the relationship between the reverse temperature dependence of hydrogen permeability and the PCT curves, the hydrogen permeability of pure Pd and Pd-X (X = Ho, Y, and Ni) alloy membranes were investigated. The pure Pd and Pd-5 mol%Ni alloy membranes, in which the α-α’ phase transition occurs, exhibits more significant peak behaviors than Pd-5 mol%Ho, Pd-5 mol%Y, and Pd-23 mol%Ag alloy membranes, in which the α-α’ phase transition is suppressed. Large differences in hydrogen solubility, at the hydrogen pressures above and below the plateau region or the inflection point, make the peak behaviors more significant. It is revealed that the peak temperature can be roughly predicted by the hydrogen pressure at the plateau regions or the inflection points in the PCT curves.

A Review for Consistent Analysis of Hydrogen Permeability through Dense Metallic Membranes.

The hydrogen permeation coefficient (ϕ) is generally used as a measure to show hydrogen permeation ability through dense metallic membranes, which is the product of the Fick’s diffusion coefficient (D) and the Sieverts’ solubility constant (K). However, the hydrogen permeability of metal membranes cannot be analyzed consistently with this conventional description. In this paper, various methods for consistent analysis of hydrogen permeability are reviewed. The derivations of the descriptions are explained in detail and four applications of the consistent descriptions of hydrogen permeability are introduced: (1) prediction of hydrogen flux under given conditions, (2) comparability of hydrogen permeability, (3) understanding of the anomalous temperature dependence of hydrogen permeability of Pd-Ag alloy membrane, and (4) design of alloy composition of non-Pd-based alloy membranes to satisfy both high hydrogen permeability together with strong resistance to hydrogen embrittlement.

Study on the reaction mechanism of acetylene selective hydrogenation catalysts Pd-Ag/Al2O3

Taking active component Pd-Ag alloy and catalyst carrier Al2O3 as the research object, the catalytic mechanism of acetylene hydrogenation reaction was explored by quantum mechanics theory and Monte Carlo method. In this paper, the activation energy on the catalyst surface, H2 dissociation process, acetylene and ethylene hydrogenation reaction were calculated. From the thermodynamic point of view, the increase of the co-catalyst Ag content enhances the desorption of ethylene on the catalyst surface, reduces the probability of ethane formation, and thus enhances the selectivity of acetylene hydrogenation. Through further process simulation studies, the quantum chemistry method and Monte Carlo method can be used to obtain the mechanism and optimal conditions for the selective catalytic hydrogenation of acetylene, with saving a lot of manpower and material resources.

Understanding the influence of the composition of the Ag[sbnd]Pd catalysts on the selective formic acid decomposition and subsequent levulinic acid hydrogenation

Formic acid is obtained in equimolar amount with levulinic acid during the hydrolysis of cellulose and thus can be used as a sustainable hydrogen source in the direct levulinic acid hydrogenation towards gamma-valerolactone (biofuel additive). AgPd catalysts prepared by various methods and containing different Ag:Pd ratio were investigated in this context. By combining activity tests, characterization of the main physicochemical properties of the catalysts and DFT study of formic acid decomposition, the key factors responsible for the activity of AgPd catalysts in both the formic acid decomposition and the subsequent hydrogenation of levulinic acid were specified. Pd is shown to be active, but prone to poisoning by CO, while the CO poisoning remains limited on diluted AgPd alloy with strong intermetallic interaction, where its adsorption is very weak thanks to the isolation of Pd atoms. Therefore, the catalyst containing 4%Ag-1%Pd/AlOOH showed the highest selectivity in formic acid decomposition as well as the highest activity in levulinic acid hydrogenation (34% conversion in 5 h at 190 °C).

Interfacial Engineering of PdAg/TiO2 with a Metal–Organic Framework to Promote the Hydrogenation of CO2 to Formic Acid

The interfacial postmodification of PdAg alloy nanoparticles (NPs) supported on TiO2 was performed, using the widely studied metal–organic framework ZIF-8. The resulting PdAg/TiO2@ZIF-8 enhanced th...

Pd3Ag(111) as a Model System for Hydrogen Separation Membranes: Combined Effects of CO Adsorption and Surface Termination on the Activation of Molecular Hydrogen

The co-adsorption of hydrogen and carbon monoxide on Pd3Ag(111) alloy surfaces has been studied as a model system for Pd-Ag alloys in membrane and catalysis applications using periodic density functional theory calculations (PW91-GGA). We explored the effects of Pd–Ag surface composition, since segregation of silver towards and away from the surface has been suggested to explain the experimentally observed changes in H2 activation, CO inhibition and reactivity. We found that CO pre-adsorbed on the surface weakens the adsorption of H on Pd3Ag(111) alloy surfaces irrespective of whether the surface termination corresponds to the bulk Pd3Ag composition, or is purely Pd-terminated. A higher coverage of H with CO present is obtained for the Pd-terminated surface; this surface also exhibits a larger range of chemical potentials for co-adsorbed hydrogen and CO. The barrier for H2 activation increases with increasing CO coverage, but the surface composition has the largest impact on H2 activation at intermediate CO coverage. The results imply that Pd-based membranes with typically ~ 23 wt% Ag are less prone to CO poisoning if the surface becomes Pd-terminated.