Reduction parallel electrolytic

The parallel electrolytic reduction developments at Karlsruhe appear to have concentrated initially more on the reduction of Pu and U in electrode-equipped mixer-settlers in which the reduction occurred largely in the settled aqueous phase rather than in a heterogeneous mixture. It was determined that a separating membrane may njt be necessary because of the redox potentials in the U - U5 - U6 system and the absence of gaseous products at the electrodes which could lead to explosive mixtures. A pulsed column, with internals quite different from those of Allied Chemical s electropulse column, was eventually developed and successfully tested (15,26) (Fig. 4). 

Figure 2. Scheme for the reversible dissociation of a montmorillonite crystal (A) layers of a crystal, stacked parallel to each other (B) increase in basal spacing (layer distance), following uptake of water (reduction of electrolyte concentration) (C) disintegration of a crystal into individual, kinetically independent layers at low electrolyte concentration (C < 1 x 10 M of a 1 1 electrolyte). 

Using dilatometry in parallel with cyclic voltammetry (CV) measurements in lmolL 1 LiC104 EC-l,2-dimethoxy-ethane (DME), Besenhard et al. [87] found that over the voltage range of about 0.8-0.3 V (vs. Li/Li+), the HOPG crystal expands by up to 150 percent. Some of this expansion seems to be reversible, as up to 50 percent contraction due to partial deintercalation of solvated lithium cations was observed on the return step of the CV. It was concluded [87] that film formation occurs via chemical reduction of a solvated graphite intercalation compound (GIC) and that the permselective film (SEI) in fact penetrates into the bulk of the HOPG. It is important to repeat the tests conducted by Besenhard et al. [87] in other EC-based electrolytes in order to determine the severity of this phenomenon. 

Fluid bed electrodes consist of a bed of particles supported by a structure such as a coarse sinter and fluidized by an upward stream of electrolyte and two different configurations have been described where the current path is parallel or perpendicular to the direction of fluidization (Backhurst et al., 1969). Such electrodes have been used for electrosynthetic reactions and, in particular, a pilot plant for the reduction of... 

W(VI) centers. At room temperature and under mild conditions, iron release from the complexes is observed upon reduction of the Fe(III) centers. This release is controlled by the ionic strength of the medium, the nature and concentration of the anions present in the supporting electrolyte, and by the pH of the solution. This behavior parallels those described for most siderophores that depend on the same parameters. 

At this time, Bonino s research was concerned with physico-chemical problems and spectroscopical methods. In a parallel way, his laboratory activity turned to the electrolytic reduction of some natural organic substances. It was hoped that this... 

From this physical model, an electrical model of the interface can be given. Free corrosion is the association of an anodic process (iron dissolution) and a cathodic process (electrolyte reduction). Ther ore, as discussed in Section 9.2.1, the total impedance of the system near the corrosion potential is equivalent to an anodic impedance Za in parallel with a cathodic impedance Zc with a solution resistance Re added in series as shoxvn in Figure 13.13(a). The anodic impedance Za is simply depicted by a double-layer capacitance in parallel with a charge-transfer resistance (Figure 13.13(b)). The cathodic branch is described, following the method of de Levie, by a distributed impedance in space as a transmission line in the conducting macropore (Figure 13.12). The interfacial impedance of the microporous... 

In aluminium reduction cells the carbon anode is placed in the upper part of the bath parallel to the liquid aluminium layer at the bottom, which acts as the cathode. The electrolyte between these electrodes consists of cryolite melt Na3AlF6 and alumina A1203 dissolved in it it may also contain such admixtures as A1F3, CaF2 and others. Dissolving of alumina in the bulk of the cell may be described as follows ... 

During ECM, electrochemical dissolution of anode and cathodic evolution of hydrogen proceeds on the electrodes (the WP and TE, respectively). Along with these basic reactions, parallel reactions proceed concurrently, for example, oxygen anodic evolution, cathodic reduction of nitrate ions, if NaNC>3 electrolyte is used. It is important to note that electrochemical reactions in a narrow IEG result in gas evolution. The temperature of the electrolyte in the IEG and the void fraction increase as the electrolyte flows along the gap. This leads to a variation in the electrolyte conductivity that has an effect on the distributions of current and metal dissolution rate over the WP surface. The electrode processes and the processes in... 

Because the electrodeposition process involves the transfer of electrons to an electrode, by measuring the current in the electrochemical cell, it is in principle possible to calculate the amount of material deposited. If no other reaction occurs in parallel, then we can assume that the reaction at the working electrode in aqueous electrolyte is just the simple reduction of a metal (M)... 

However, the electric potential of the electrocatalyst at its interface with the electrolyte (and thus the facility for charge transfer) can be easily and extensively altered at will to control rate and selectivity. For instance, a decrease of electrode potential by about 0.15 V can change the product selectivity for vinyl fluoride and chloride reduction on palladium by as much as 80% (31). In contrast, gas phase parallel reductions, with 5 kcal/mol difference in activation energies, would require a temperature increase from 500 K to 730 K for a comparable selectivity change. We should note here that the electrocatalytic specificity of the above reductions is quite similar to that of conventional heterogeneous catalytic reactions, but differs from that of conventional electrolytic reduction on noncatalytic electrodes (32). 

The efifect of electrocatalyst and operating conditions on selectivity were examined recently for the reduction of olefinic halides to saturated halides or cleavage products (hydrogenation versus hydrogenolysis) 31. These two steps proceed in parallel at different rates on various electrocatalysts. Thus, the ability for double bond reduction decreases in the order Pd Ru > Ag > Pt, although the overall rate is about the same on Pd and Pt (cf. Table VI). Figure 24 shows the extensive variation of reaction specificity with cathode potential as well as the smaller effect of electrolyte concentration. Similar behavior is exhibited by other halides and electrodes 31. ... 

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