Papers by Keyword: Palladium

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Authors: Sandrine Cardinal, Ji Chao Qiao, Jean Marc Pelletier
Abstract: The gold alloys are used in jewelry for their aesthetic appearance and inertia to the environment. In jewelry a hardness superior to 300 HV is desirable to facilitate the final machining and reduce the wear of the final product. The maximum hardness that can be obtained with the standard 18 carats gold (Au75-Ag12.5-Cu12.5 (wt%)) through a combination of heat treatment and cold working is about 290 HV. Gold-based bulk metallic glasses (BMGs) are an alternative as they present unique properties in comparison with crystalline counterparts, especially easy thermoplastic processing combined with a high hardness. Pd-base BMGs are another solution, due also to their attractive features.An Au49Cu26.9Si16.3Ag5.5Pd2.3 (% at.) and a Pd40Cu30Ni10P20 (% at.) bulk metallic glasses were fabricated by a copper mould suction casting technique in an argon atmosphere. In the as-cast state hardness, shear modulus and hardness are high (HV0.3= 360 and 530 in the Au-and Pd-base BMGs, respectively). Various heat treatments have been performed to modify the microstructural state. Formation of crystalline particles induces an increase of both shear modulus and hardness but a drastic decrease in toughness and therefore this formation should be absolutely avoided during casting or thermo processing.
Authors: Arvind Balakrishnan, Claas Mueller, H. Reinecke
Abstract: We present a millimeter scale reactor integrated PEM fuel cell energy source with an onboard hydrogen production reactor (realized by alkaline chemical hydride), and passive hydrogen buffering unit (realized by metal hydride) of hydrogen. A stacked system of reactor-hydrogen buffer-PEM fuel cell is demonstrated. The system is driven by the hydrolysis of the alkaline chemical hydride (NaOH+NaBH4) in the presence of micro porous catalyst layer (platinum catalyst (Ni-Pt)). The produced hydrogen gas from the reactor is buffered through the hydrogen buffer (Palladium metal hydride) and gets distributed (due to the pressure difference) onto the anode of the PEM fuel cell. The operational behaviour of the complete system is investigated with the hydrogen produced from the alkaline chemical hydride and pure hydrogen gas. Long term voltage measurements under a defined electrical load of the alkaline chemical hydride driven system was measured. The increase in time for the hydrogen production observed in the long term voltage measurement is anticipated to the degradation of the Ni-Pt catalyst. The system is “self-buffering” in nature so any change in electrical load can be handled during system operation.
Authors: N.J. Creamer, I.P. Mikheenko, K. Deplanche, P. Yong, J. Wood, K. Pollmann, S. Selenska-Pobell, Lynne E. Macaskie
Abstract: Palladized biomass of typical Gram negative bacteria (Desulfovibrio desulfuricans and Escherichia coli) is well documented as a potentially useful catalyst for reduction of metallic species such as Cr(VI). This bionanocatalyst can be sourced from Pd-waste and scrap leachates via biocrystallization. A major industrial application of precious metal catalysts is in hydrogenation and hydrogenolysis reactions whereby, respectively, H is added across unsaturated bonds and halogen substituents can be removed from aromatic rings. Gram positive bacteria have not been evaluated previously as potential supported Pd-bionanocatalysts. We compare the activity of ‘Bio-Pd(0)’ supported on the fundamentally different Gram negative (Desulfovibrio) and Gram positive (Bacillus) bacterial surfaces, and evaluate the activity of the two types of ‘Bio-Pd(0)‘ in a standard reference reaction, the hydrogenation of itaconic acid, against a commercially available catalyst (5% Pd on carbon). The results show that the bionanocatalysts have a similar activity to the commercial material and biomanufacturing from waste sources may be an economic alternative to conventional processing for catalyst production as precious metal prices continue to rise.
Authors: Hong Yu Wang, Xin Le Zhao, Bing Jun Shen, Li Hong Jin, Xin Lu, Jian Tian
Abstract: This article by palladium deuterium gas-solid experimental system design, combined with the DH1716A program-controlled DC stabilized current supply and Keithley 2700 data acquisition and recording system, respectively at five different pressures, pressures triggered by experimental methods, making experiments of deuterated Palladium chemical reactions within the system, resulting in a tile level under different pressures is overheating.
Authors: Ivan Venegoni, Matteo Consonni, Irene Bianchi, Enrica Ravizza, Salvatore Grasso, Simona Spadoni, Mario Pistoni, Paolo Colpani
Authors: Shigeki Hara, Misaki Ishitsuka, Hiroyuki Suda, Masakazu Mukaida, Kenji Haraya
Abstract: Some dense metal membranes are permeable only to hydrogen, useful to produce and purify hydrogen. Conventionally, hydrogen permeation flux through metal membranes is described as the square-root law. The permeability defined in the law is commonly used as a measure of membrane material. However, deviation from the law has been widely reported. We have extended the definition of permeability for precise description. This study applied it to a thick palladium membrane down to 0.01 MPa in absolute pressure. Experimental results showed that hydrogen permeation flux through the palladium membrane 200 μm thick did not obey the square-root law completely. From the permeation behavior, pressure-dependent permeability was evaluated. The resultant permeability was found to decrease and become a constant value, or intrinsic permeability, as pressure approached vacuum.
Authors: Akihiro Nakai, Masayuki Mizumoto, Akio Kagawa
Abstract: A power actuator based on a great volume expansion on hydrogenation of hydrogen storage alloys (HSAs) has been developed. The actuator has a bimorph structure consisting of Pd-Ni alloy and Cu-plating to convert the volume change into bending motion. The techniques to control the bending and rotation motions of the actuator were investigated by adjusting alloy composition, shape and the amount of hydrogen absorbed in the HSA. It is found that Pd-Ni alloy actuators exhibit a cyclic bending motion on hydrogen absorption and desorption cycles and the bending behavior can be controlled by controlling the hydrogen pressure. When a ribbon shaped actuator was deformed into the “L” shape on the transverse section, a rotation motion was observed without modifying the basic bimorph structure of the actuator.
Authors: Xian Zhong Mo, Hua Lin Hu, Deng Feng Tan, Ting Guo
Abstract: 5A zeolite supported Gold-Palladium (Au-Pd) bimetallic were prepared and used in vapor phase oxidation of ethylene to synthetize vinyl acetate (VA). The chemical composition of Au-Pd/5A zeolite catalyst was analyzed by a combination of atomic absorption spectrometry (AAS). The structure of Au-Pd/5A zeolite catalyst was characterized by a scanning electron microscopy (SEM) and X-ray diffraction (XRD). The catalytic activity of the Au-Pd/5A zeolite catalyst under laboratory conditions were investigated in vinyl acetate synthesis by a kind of the fixed bed reaction device. The AAS testing showed that Au and Pd supported rate were increased up to the optimum value 91.22% and 93.91% respectively at the ratio of Au/Pd=0.87. The SEM analysis results indicated that Au-Pd alloy particles of 5A zeolite catalyst can grown up and reunited obviously through before and after reaction. The XRD analysis results showed that diffraction peak of Pd (111), Pd (200), Au (111) and Au (200) became sharp gradually with the extension of reaction time, crystalline phase composition and grain size of catalyst became bigger gradually. The results about catalytic activity of the Au-Pd/5A zeolite catalyst shown that with the increasing of the Au/Pd ratio, the space-time yield and selectivity have a best value respectively; when the ratio of Au/Pd=0.87, the space-time yield were 702g/(Lh) and the selectivity were 92.8% at the ratio of Au/Pd =1.13.
Authors: Volker Engels, Andrew E.H. Wheatley, Angel Berenguer-Murcia, David A. Jefferson, Brian F.G. Johnson
Abstract: Novel catalytic systems based on PdZn alloys have been synthesized by polyol reduction over the entire compositional range [1, 2] and characterized by means of HRTEM, EDS and ICP. The expected bulk compositions were reproducible to within a 2 mol% margin and the purified particle suspensions stable for several months after preparation. The EDS results indicated the presence of considerable amounts of oxygen, especially in those samples containing high fractions of zinc. The particle size distributions were shown to be narrow and the mean sizes slightly decreased with higher molar fractions of palladium (diameter range 2.6 to 3.2 nm). In the catalytic hydrogenation of phenylacetylene, a strong dependence of the substrate conversion time on the Pd concentration was established, and selectivity towards the semihydrogenation product (styrene) was found to be close to 100 %. The selectivity dropped only shortly before the initial substrate was fully depleted.
Authors: P. Yong, I.P. Mikheenko, K. Deplanche, F. Sargent, Lynne E. Macaskie
Abstract: Bio-manufacturing of nano-scale palladium was achieved using bacterial cells. Highly active Pd-catalyst (Bio-Pd) produced by an E. coli mutant gave power output in a fuel cell. Up to ~115% of the maximum power generation was achieved by electrodes of Bio-Pd catalysts from Escherichia coli, compared to that from a commercial-Pd electrode (~0.099 W). A bio-precious-metals (Bio-PM) catalyst made directly from an industrial reprocessing solution by the E. coli was also made into fuel cell electrodes and ~0.06W of maximum power generation was observed.
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