Palladium diffusion

There are several methods used to purify gases catalytic adsorption, palladium diffusion, gettering, chemisorption, and filtration. 

Palladium Diffusion. Palladium is very permeable to hydrogen but not permeable to other gases. As a result, it is a useful hydrogen purifier. A palladium membrane, heated to 400 °C, purifies hydrogen to <10 ppb but requires a high pressure differential for net diffusion to take place at reasonable rates of hydrogen supply. 

Price, F. C. 1965. Palladium diffusion yields high-volume hydrogen. Chem. Eng. 72(5) 36-38. 

Konishi, S., Yoshida, H., and Naruse, Y., A design study of a palladium diffuser for D-T fusion reactor fuel clean-up system, J. Less-Comm. Met., 89, 457, 1983. 

The proposed method of concentration by removing part of the carrier gas is sufficiently general. It seems that with a mixed carrier gas one component of which is hydrogen one can provide for absorption of the latter by using palladium black on asbestos or palladium diffusion tubes. One can also use a carrier gas the components of which react with the result that the volume decreases. 

Interdiflusion between the components of catalyst coatings and substrates can also lead to catalyst deactivation. If Nb, Ta, Ti, V or Zr diffuses through palladium or other noble metal protective layers and reacts on the outer surface to form stable oxides, carbides or nitrides, the catalytic dissociation of molecular hydrogen can be poisoned. Interdiffusion, linked to loss of hydrogen flux, has been reported by Edlund and McCarthy [47] and Pagheri et al. [56]. Membrane surfaces can also become depleted of palladium if palladium diffuses into the substrates. Apparent complete loss of palladium has been observed by Rothenberger et al. for 40 nm thick Pd films on Ta foils after 48 h use at 1173 K (900 °C) [41]. 

Figure 8.16 shows a methanol/water vaporiser, followed by a catalytic steam reformer operating at about 250°C, in which the catalyst is a thin film of Cu/ZnO coated onto the silica reactor, and finally a membrane shift reactor consisting of a palladium diffusion layer mounted on top of a perforated copper-based shift catalyst. Built onto the chip are integrated resistive heaters for getting the reformer and vaporiser up to temperature, together with micro-scale sensors and control electronics. Whilst such systems are a long... 

The necessity of having absolutely pure hydrogen on hand can be overcome by a simple trick (although thanks to the commercially available palladium diffusion purifiers this is no longer a big problem) One can electrolytically generate the hydrogen itself at the platinum electrode with the help of an additional electrode and a cur-... 

The remarkable solubility of hydrogen in palladium discovered by T. Graham following the observation of hydrogen diffusion through red-hot platinum and iron by H. St. C. Deville and L. Troost, 1863. 

An interesting approach to the inter-diffusion problem was made by Rhys S who protected ruthenium-rich ruthenium-gold alloys by palladium-... 

The main uses of palladium [13] are in the electronics and electrical industries, in circuitry and in dental alloys. It finds many catalytic applications in industry, as well as in diffusion cells for the synthesis of hydrogen, and in automobile catalysts. Jewellery and three way auto-catalysts are the principal uses of platinum, which fulfils a wide range of roles in the chemical industry. 

When studying the kinetics of diffusion of hydrogen through palladium, Farkas (28) noticed the difference in catalytic activity of both sides of the palladium disks or tubes for the parahydrogen conversion the energy of activation was greater on the inlet side than on the outlet side, where due to extensive desorption of the hydrogen its concentration could be lower. 

Moreover, in the case of hydride intervention, still a further factor, namely the kinetics of hydrogen diffusion into the metal, influences also the overall kinetics by removing a reactant from a reaction zone. In order to compare the velocity of reaction of hydrogen, catalyzed by palladium, with the velocity of the same reaction proceeding on the palladium hydride catalyst, it might be necessary to conduct the kinetic investigations under conditions when no hydride formation is possible and also when a specially prepared hydride is present in the system from the very beginning. 

Johnson et al. (J5) have used the hydrogenation of a-methylstyrene catalyzed by palladium-alumina in powder form in agitated vessels. The physical diffusion of hydrogen through the liquid is the rate-controlling step. The total resistance of this transfer consisted of two separate resistances, one in the liquid adjoining the bubbles and another in the liquid adjoining the suspended solid particles. 

Very few studies on complexes of palladium and platinum with 1,1-dithiolato ligands have been reported recently. The electronic absorption spectra of the Et2dtc complexes of Pd and Pt, as well as Zn, Cu, Fe, Co, and Mn, have been measured in MeCN, EtOH, and -heptane, with diffuse-reflectance spectra also being determined (401). In 1969 and... 

Figure 27, Estimation of CO in blood with a Conway diffusion dish. Palladium chhride is reduced to black palladium powder in the center compartment by the...

Room temperature deposition of silver on Pd(lOO) produces a rather sharp Ag/Pd interface [62]. The interaction with a palladium surface induces a shift of Ag 3d core levels to lower binding energies (up to 0.7 eV) while the Pd 3d level BE, is virtually unchanged. In the same time silver deposition alters the palladium valence band already at small silver coverage. Annealing of the Ag/Pd system at 520 K induces inter-diffusion of Ag and Pd atoms at all silver coverage. In the case when silver multilayer was deposited on the palladium surface, the layered silver transforms into a clustered structure slightly enriched with Pd atoms. A hybridization of the localized Pd 4d level and the silver sp-band produces virtual bound state at 2eV below the Fermi level. 

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