Catalyst anodic oxidation

The purple permanganate ion [14333-13-2], MnOu can be obtained from lower valent manganese compounds by a wide variety of reactions, eg, from manganese metal by anodic oxidation from Mn(II) solution by oxidants such as o2one, periodate, bismuthate, and persulfate (using Ag" as catalyst), lead peroxide in acid, or chlorine in base or from MnO by disproportionation, or chemical or electrochemical oxidation. 

Process Miniaturization Second International Conference, CATTECH, December 1998 Steep progress in microelectronics in the past key players topics of IMRET 2 general advantages of micro flow energy, safety, process development, combinatorial catalyst testing, lab-on-a-chip biological applications anodically oxidized catalyst supports as alternatives to non-porous supports [220]. 

Daumengrofes Labor aus Aluminium-Folie, Blick durch die Wirtschafi, June 1997 Heterogeneous gas-phase micro reactor micro-fabrication of this device anodic oxidation of aluminum to porous catalyst support vision of complete small laboratory numbering-up development of new silicon device [225]. 

Mikroreaktoren sind so klein wie ein Fingerhut, Handdsblatt, May 1998 Steep progress in microelectronics, sensor and analytical techniques in the past transport intensification for catalysis first catalytic micro reactors available partial oxidation to acrolein partial hydrogenation to cyclododecene anodically oxidized catalyst supports as alternatives to non-porous supports study group on micro reactors at Dechema safety, selectivity, high pressure exclusion of using particle solutions limited experience with lifetime of micro reactors [236],... 

For this micro reactor version, the microstructured platelets were treated by anodic oxidation to obtain a nano-porous layer and impregnated with precursor solutions in organic solvents to obtain a V205 P205 Ti02 catalyst. 

Operating pressure 1.2 bar Catalyst material formation 3oTi7oOx Si02 suspension + impregnation finally anodic oxidation... 

GP 2] [R 3a] The performance of one micro reactor with three kinds of catalyst -construction material silver, sputtered silver (dense) on aluminum alloy (AlMg3), and sputtered silver on anodically oxidized (porous) aluminum alloy (AlMg3) -was compared with three fixed beds with the same catalysts [44]. The fixed beds were built up by hackled silver foils, aluminum wires (silver sputtered) and hack-led aluminum foils (anodically oxidized and silver sputtered), all having the same catalytic surface area as the micro channels. Results were compared at the same flow rate per unit surface area. 

Of particular concern was the finding of a suitable catalyst Owing to the scouting nature, virtually no know-how base was available that time. The investigation gave highly valuable hints for later catalyst development. Actually, they motivated a search for catalysts of higher porosity and better defined composition. As a result, anodically oxidized alumina supports for catalysts were developed (see Sections 3.1 and 3.4.2). 

A nanoporous structure on the surface of the micro channels can be realized via anodic oxidation, thereby considerably enlarging the catalyst surface [17]. Catalysts... 

P 17] In order to have a catalyst with a sufficiently high specific surface area, pretreatment of the micro channels made of aluminum was necessary [17], Following a cleaning procedure, an oxide layer with a regular system of nanopores was generated by anodic oxidation (1.5% oxalic acid 25 °C 50 V DC 2 h exposure using an aluminum plate cathode followed by calcination). 

Low-valent lanthanides represented by Sm(II) compounds induce one-electron reduction. Recycling of the Sm(II) species is first performed by electrochemical reduction of the Sm(III) species [32], In one-component cell electrolysis, the use of sacrificial anodes of Mg or A1 allows the samarium-catalyzed pinacol coupling. Samarium alkoxides are involved in the transmet-allation reaction of Sm(III)/Mg(II), liberating the Sm(III) species followed by further electrochemical reduction to re-enter the catalytic cycle. The Mg(II) ion is formed in situ by anodic oxidation. SmCl3 can be used in DMF or NMP as a catalyst precursor without the preparation of air- and water-sensitive Sm(II) derivatives such as Sml2 or Cp2Sm. 

J. Sfeir, P A. Buffat, P. Mockli, N. Xanthopoulos, R. Vasquez, H. J. Mathieu, J. Van herle, and K. Ravindranathan Thampi, Lanthanum chromite based catalysts for oxidation of methane directly on SOFC anode, J. Catal. 202, 229-244 (2001). 

The electrochemical Wacker-type oxidation of terminal olefins (111) by using palladium chloride or palladium acetate in the presence of a suitable oxidant leading to 2-alkanones (112) has been intensively studied. As recyclable double-mediatory systems (Scheme 43), quinone, ferric chloride, copper acetate, and triphenylamine have been used as co-oxidizing agents for regeneration of the Pd(II) catalyst [151]. The palladium-catalyzed anodic oxidation of... 

For the transfer of redox electrons (inner-sphere electron transfer) in which redox particles are adsorbed on a thin superficial film that covers a metal electrode, the transfer current of redox electrons is not always decreased but rather increased by the presence of the thin film. Such an increase in the reaction ciurent will occur, if the film acts as a reaction catalyst providing the adsorbed state of redox particles favorable for the redox electron transfer. For example, the anodic oxidation of carbon monoxide is catalyzed by the presence of an anodic oxide film on... 

Carbon Monoxide The presence of CO in a H2-rich fuel has a significant effect on anode performance because CO affects Pt electrodes catalysts. The poisoning is reported to arise from the dual site replacement of one H2 molecule by two CO molecules on the R surface (40, 41). According to this model, the anodic oxidation current at a fixed overpotential, with (ico) and without (in2) CO present, is given as a function of CO coverage (0co) by Equation (5-11) ... 

The ruthenium tetroxide dioxide catalytic system is effective for the oxidation of alkanols, although it will also react with any alkene groups or amine substituents that are present. The catalyst can be used in aqueous acetonitrile containing tetra-butylammonium hydroxide with platinum electrodes in an undivided cell Primary alcohols are oxidised to the aldehyde and secondary alcohols to the ketone [30]. Anodic oxidation of ruthenium dioxide generates the tetroxide, which is the effective oxidising agent. 

The use of nitroxyls that are amenable to immobilisation in a polymer layer around the anode would be an ideal way of constraining the catalyst where it can be regenerated electrochemically. Attempts to utilise a poly(pyrrole) film formed by anodic oxidation of the monomer 5 led to a system that will oxidise alkanols but which is unstable in continuous use [40], A more satisfactory polymer layer is... 

Cobalt(II) acetate is used for bleaching and drying varnishes and laquers. Other applications are as a foam stahihzer for beverages in sympathetic inks as a mineral supplement in animal feed and as a catalyst for oxidation. It also is used in aluminum anodizing solutions. 

Fig. 3 Concept of nanoengineering of oxide catalytic surface in terms of nanoreactor array, some of the possibilities offered by this concept (in particular in terms of realizing multifunctional catalysts for cascade reactions in nanoconfined liquids) and a SEM image of an array of Xi02 nanotubes produced by anodic oxidation of Ti foils. Source Centi et alN...

Fig. 7 FESEM images of titania nanocoil produced by anodic oxidation (a). The cartoon shows schematically the photocurrent generated by light irradiation of nanocoil containing a catalyst particle (b) and the associated magnetic field (c). Source Centi and Perathoner. ...

Usually the nanotube arrays have been made from a titanium thick film or foil, in which case the resulting nanotubes rest upon an underlying Ti substrate as separated by a barrier layer. The nanotube arrays have also been fabricated from a titanium thin film sputtered onto a variety of substrates, such as silicon and fluorine doped tin oxide (FTO) coated conductive glass. This extends the possibility for preparing technical catalysts by deposing a thin Ti layer over a substrate (a foam, for example) and then inducing the formation of the nanostructured titania film by anodic oxidation. ... 

Other sources of radical CF3, much less expensive than CF3I, have been discovered. These are the anodic oxidation of sodium trifluoroacetate (the decomposition being initated by a hydroperoxide or ruthenium catalyst) and trifluoromethyl bromide (CF3Br) using sodium dithionite as initiating agent. ... 

Mediated electrochemical oxidation (MEO) is an ex situ treatment technology that uses electricity, acid, and a metal catalyst to destroy organic wastes at low temperatures and pressures. The proprietary CerOx Corporation MEO configuration uses cerium metal as a catalyst to oxidize organic waste into carbon dioxide and water. The process occurs in an acidic solution, typically nitric acid. The first step involves the generation of an oxidant at the anode, followed by the reduction of water or another chemical species at the cathode. This technology serves as a nonthermal alternative to incineration. 

Electrocatalysis in fuel cells requires as well substances capable of catalyzing the anodic oxidation of fuels as catalysts for the cathodic reduction of oxygen. Several dyestuffs that catalyze oxygen reduction are known, but up to now only one has been described as active in anodic reactions. All these dyestuffs are N4-chelates. 

Parallel to this work, catalysts for the anodic oxidation of several fuels were established 10>. Up to now, however, only one chelate is known to catalyze anodic reactions the cobalt complex of dihydro-dibenzo-tetra-aza-annulene. 

These properties make CoTAA a good catalyst for the anodic oxidation of formic acid. Economic application of this catalyst is, however, not anticipated because formic acid is not economically attractive as a fuel. It is certainly possible to prepare electrodes containing a mixture of tungsten carbide and CoTAA as catalyst, with the tungsten carbide catalyzing the first stage of the oxidation of CH2O to HCOOH, and the CoTAA the further oxidation of HCOOH to CO 2, but this possibility does not offer any more favorable prospects. Economic application of CoTAA will only come into question when cheap catalysts are available for the partial oxidization of methanol to formaldehyde or formic acid. 

Catalyst deterioration due to gas poisoning is only avoided by careful gas cleaning. Anodic oxidation followed by dissolution of Pt and transfer to the cathode is a serious cause for Pt loss. It is potential dependent and accelerates as the cathode potential increases, for instance under partial load or in off-time, when the cathode potential drifts toward the oxygen equilibrium potential. Therefore it is of utmost importance that whenever the fuel cell is switched off, the oxygen in the cathode lumen is rapidly exchanged by inert nitrogen and that the cell voltage under operation does not surmount 0.8 V. 

Figure 24 depicts schematically the concentration profile of dissolved hydrogen in a porous catalyst particle brought about by interaction of diffusive mass transport of hydrogen into the porous catalyst particles and the consumption of hydrogen by anodic oxidation at the inner surface of the catalyst. 

The loss of the catalytically active surface of Raney nickel due to recrystallization is a continuously progressing process that can be retarded to some extent in Raney-nickel anodes by dispersing oxide ceramic materials like Zr02 and Ti03 in the nickel matrix. More serious is anodic oxidation for some metals additionally accompanied by dissolution of the catalyst to which even platinum is subject but which is an even more serious hazard for the less noble catalysts as silver and Raney nickel. 

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