Reduction of lead oxides

Once the thermal runaway had become established, the high temperature could allow a smelting reaction (reduction of lead oxides by carbon to metallic lead) to occur, and the low m.p. and high density (327°C, 10.6, respectively) would cause the molten lead to concentrate at the base of the reactor, decreasing the lead content and raising the manganese content of the bulk of the clinker residue, as was observed [2],... 

Hasse U, Scholz F (2001) In situ atomic force microscopy of the reduction of lead oxide nanocrystals immobihsed on an electrode surface. Electrochem Commun 3 429-434. 

Experiment 177. — (a) Recall or repeat the reduction of lead oxide in the blowpipe flame. 

Obviously, the kinetics of the overall process will be influenced by both the partial reductive dissolution and the kinetics of the nucleation/growth of the deposit of Co metal. This process may involve intermediate cobalt species in solution or proceed via solid-to-solid conversion to a metal phase, as described by Hasse and Scholz (2001) for the reduction of lead oxide. The properties of the metallic deposit are remarkably different for each of the studied materials, as denoted by the observed differences in their anodic behavior. The oxidation signal at -e0.40 V can be described in terms of total or partial oxidative dissolution processes ... 

The reaction of COj with coke to form CO is endothermic and will reduce the temperature in this zone, but will be counteracted to some extent by the reduction of lead oxides, which is exothermic. 

The sinter plant-blast furnace process involves two stages, firstly fully oxidising sulfides to oxides, followed by reduction of lead oxide to metal, as shown in Equations 7.1 and 7.2. The same end point can be reached by partial oxidation only, as indicated by Equation 7.3. 

The dissolution of carbon in molten iron in the lower part of the furnace, leads to the reduction of manganese oxide (eq. 15) and some sihea (eq. 14), both in the slag, whereby the subsequent dissolution of these metals occurs in the molten iron. 

Stable oxides, such as those of clrromium, vanadium and titanium cannot be reduced to the metal by carbon and tire production of these metals, which have melting points above 2000 K, would lead to a refractoty solid containing carbon. The co-reduction of the oxides widr iron oxide leads to the formation of lower melting products, the feno-alloys, and tlris process is successfully used in industrial production. Since these metals form such stable oxides and carbides, tire process based on carbon reduction in a blast furnace would appear to be unsatisfactory, unless a product samrated with carbon is acceptable. This could not be decarburized by oxygen blowing without significairt re-oxidation of the refractory metal. 

Methanol is sometimes used to prepare dichromium trioxide by the reduction of chromium oxide (Vi). Since these attempts lead to spontaneous ignition and detonation, it is preferable to use the thermal decomposition of ammonium dichromate, provided it is carried out with caution (see p.200). 

The impurities that occur in the crude zinc produced by the carbothermic reduction of zinc oxide are 2-3% lead, 0.3-0.4% cadmium, and 0.05% iron. Zinc is more volatile than... 

The first pathway proposed by Iizuka and Lunsford [17] considers the reduction of nitric oxide by CO over rhodium/Y-zeolite. It leads only to N20 as follows ... 

Steric factors are also important in hydrodimerizations carried out in acidic media. Excessive steric hindrance about the 0-carbon in an a, 0-unsaturated carbonyl compound can retard tail-to-tail coupling, e.g., 2 130 - 131, and lead to products of head-to-head (and occasionally head-to-tail) coupling. Thus in the reduction of mesityl oxide at pH lg.4 there is also formed a small amount of ketone 140, apparently formed via head-to-head coupling of 130 and subsequent pinacol rearrangement of 139 134) ... 

The finely divided lead produced by reduction of the oxide with furfural vapour at 290°C is pyrophoric and chemically reactive. 

Hock and Kropf [253] studied cumene oxidation catalyzed by Pb02. They proposed that Pb02 decomposed cumyl hydroperoxide (ROOH) into free radicals (R0 , R02 ). The free radicals started the chain oxidation of cumene in the liquid phase. Lead dioxide introduced into cumene was found to be reduced to lead oxide. The reduction product lead oxide was found to possess catalytic activity. The following tentative mechanism was proposed. 

The production of germanium and silicon is carried out by the reduction of the oxides, SiCh and GeC>2. There is a considerable difference in the stabilities of the oxides, and GeC>2 can be reduced by hydrogen at temperatures around 1100K, but SiC>2 must be reduced by carbon at temperatures around 2300 K. The elements only reach a vapour pressure of 10-6 atmos at 1500 K and 1750 K respectively, and so the reduction of GeC>2 does not lead to any significant vaporization, but this is not so in the production of silicon. The gaseous composition of a 1 2 mixture of Si(>2 and carbon at 2000 K is as follows ... 

Molybdenum was first identified as a distinct element by Swedish chemist Karl Wilhelm Scheele in 1778. The metal was isolated by Hjelm in 1782 by reduction of its oxide with carbon. Moissan in 1895 isolated the metal in highly purified form by electrolytic reduction of its oxide and studied many of its physical and chemical properties. The element derived its name in 1816 from the word molybdos, meaning a soft mineral that appeared like lead. 

Pt-Rh/AROs catalysts are widely used in automotive-exhaust emission control. In these systems, Pt is generally used for the oxidation of CO and hydrocarbons and Rh is active for the reduction of nitric oxide to N2. HRTEM and AEM show two discrete particle morphologies and Pt-Rh alloy particles (Lakis et al 1995). EM studies aimed at understanding the factors leading to deactivation, surface segregation of one metal over the other and SMSI are limited. There are great opportunities for EM studies, in particular, of surface enrichment, and defects and dislocations in the complex alloy catalysts as sites for SMSI. 

Upon repetitive cycling of the potential scan, the voltammetric record is reproduced, but an additional cathodic peak near to -0.45 V appears. This is due to the reduction of Pb + ions electrochemically generated by the previous oxidation of lead metal. The reduction of lead ions occurs at a potential different from that at which the reduction of PbCOs takes place. In repetitive voltammetry, additional anodic peaks appear at -0.40 and -0.28 V. These are due to the oxidative dissolution of different lead deposits generated in reductive scans [130, 131]. 

Besides the broad applications of electrically contacted enzyme electrodes as amperometric biosensors, substantial recent research efforts are directed to the integration of these functional electrodes as biofuel cell devices. The biofuel cell consists of an electrically contacted enzyme electrode acting as anode, where the oxidation of the fuel occurs, and an electrically wired cathode, where the biocatalyzed reduction of the oxidizer proceeds (Fig. 12.4a). The biocatalytic transformations occurring at the anode and the cathode lead to the oxidation of the fuel substrate and the reduction of the oxidizer, with the concomitant generation of a current through the external circuit. Such biofuel cells can, in principle, transform chemical energy stored in biomass into electrical energy. Also, the use... 

Relationships of other type are observed in the case where both the conjugated reactions proceed through the same band (Fig. 13b). For example, the cathodic reaction (42b) can take place with the participation of valence electrons rather than conduction electrons, as was assumed above. Thus, reduction of an oxidizer leads to the injection of holes into the semiconductor, which are used then in the anodic reaction of semiconductor oxidation. In other words, the cathodic partial reaction provides the anodic partial reaction with free carriers of an appropriate type, so that in this case corrosion kinetics is not limited by the supply of holes from the bulk of a semiconductor to its surface. Here the conjugated reactions are in no way independent ones. 

Chemical reduction of azine //-oxides, depending on substrate structure, reductant and reaction conditions can proceed both with or without deoxygenation of the N-atom. Thus, 1,2,3-triazine 1-oxide (337) with NaBH4 gives 2,5-dihydro-1,2,3-triazine (336), suggesting that the N-oxide moiety back-donates electrons to the triazine ring. On the other hand, on reduction of the isomeric 2-oxide leading to tetrahydro derivatives (338) and (339) the N-oxide function is not touched (82H(17)317). 

Azoxybenzene has been prepared by reduction of nitrobenzene with alcoholic potassium hydroxide,1 with sodium amalgam,2 with hydrogen in the presence of lead oxide,3 with methyl alcohol and sodium hydroxide,4 with sodium methylate and methyl alcohol,5 and by electrolytic reduction 6 by oxidation of azobenzene with chromic anhydride 7 by treatment of /9-phenylhydroxylamine with alkaline potassium permanganate,8 with nitrobenzene,9 with mineral adds,10 and with mercury acetamide,11 and by oxidation of aniline with hydrogen peroxide,12 and with acid permanganate solution in the presence of formaldehyde.13 The procedure described above is a slight modification of one described in the literature.14... 

An electron is excited from the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO) when a molecule in solution absorbs light. The excited electron in the LUMO may transfer to a neighboring molecule (oxidant) in solution, leading to the reduction of the oxidant, whereas the electronic hole (electron vacancy) in the HOMO may transfer to another neighboring molecule (reductant) in solution, resulting in the oxidation of the reductant. Quite similar photoinduced reduction-oxidation processes can occur at the semiconductor/solution (semiconductor/liquid) interface when a semiconductor in solution absorbs light. Fig. 4.1 schematically illustrates the... 

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