Formaldehyde, electrochemical

The conventional electrochemical reduction of carbon dioxide tends to give formic acid as the major product, which can be obtained with a 90% current efficiency using, for example, indium, tin, or mercury cathodes. Being able to convert CO2 initially to formates or formaldehyde is in itself significant. In our direct oxidation liquid feed fuel cell, varied oxygenates such as formaldehyde, formic acid and methyl formate, dimethoxymethane, trimethoxymethane, trioxane, and dimethyl carbonate are all useful fuels. At the same time, they can also be readily reduced further to methyl alcohol by varied chemical or enzymatic processes. 

Other applications of zirconium tetrafluoride are in molten salt reactor experiments as a catalyst for the fluorination of chloroacetone to chlorofluoroacetone (17,18) as a catalyst for olefin polymerization (19) as a catalyst for the conversion of a mixture of formaldehyde, acetaldehyde, and ammonia (in the ratio of 1 1 3 3) to pyridine (20) as an inhibitor for the combustion of NH CIO (21) in rechargeable electrochemical cells (22) and in dental applications (23) (see Dentalmaterials). 

Ethylene glycol can be produced by an electrohydrodimerization of formaldehyde (16). The process has a number of variables necessary for optimum current efficiency including pH, electrolyte, temperature, methanol concentration, electrode materials, and cell design. Other methods include production of valuable oxidized materials at the electrochemical cell s anode simultaneous with formation of glycol at the cathode (17). The compound formed at the anode maybe used for commercial value direcdy, or coupled as an oxidant in a separate process. 

Many electroless coppers also have extended process Hves. Bailout, the process solution that is removed and periodically replaced by Hquid replenishment solution, must still be treated. Better waste treatment processes mean that removal of the copper from electroless copper complexes is easier. Methods have been developed to eliminate formaldehyde in wastewater, using hydrogen peroxide (qv) or other chemicals, or by electrochemical methods. Ion exchange (qv) and electro dialysis methods are available for bath life extension and waste minimi2ation of electroless nickel plating baths (see... 

It is readily reduced to Me amine, and a number of chem, catalytic, and electrochem procedures have been used (Ref 10). 2) In most cases the redns can be stopped at the hydroxyl-amine stage to give N-Me hydroxylamine (Ref 10). 3) The action of strong acids on salts of NMe gives derivs of formaldehyde (Ref 10). 

H. Baltruschat, N.A. Anastasijevic, M. Beltowska-Brzezinska, G. Hambitzer, and J. Heitbaum, Electrochemical detection of organic gases The development of a formaldehyde sensor, Ber. Buns. Phys. Chem. 94, 996-1000 (1990). 

Korzeniewski C, Childers CL. 1998. Formaldehyde yields from methanol electrochemical oxidation on platinum. J Phys Chem B 102 489-492. 

Shropshire JA. 1965. The catalysis of the electrochemical oxidation of formaldehyde and methanol by molybdates. J Electrochem Soc 112 465-469. 

Chen Y-X, Heinen M, Jusys Z, Behm RJ. Dissociative adsorption and oxidation of formaldehyde on a Pt film electrode under controlled mass-transport conditions, an in-situ spectro-electrochemical flow-cell study. To he published. 

JusysZ. 1994. H/D substitution effect on formaldehyde oxidation rate at a copper anode in alkaline medium studied by differential electrochemical mass spectrometry. J Electroanal Chem 375 257-262. 

A simplified scheme of the dual pathway electrochemical methanol oxidation on Pt resulting from recent advances in the understanding of the reaction mechanism [Cao et al., 2005 Housmans et al, 2006] is shown in Fig. 15.10. The term dual pathway encompasses two reaction routes one ( indirect ) occurring via the intermediate formation of COads. and the other ( direct ) proceeding through partial oxidation products such as formaldehyde. 

A calculation of the temperature dependence of the free energy for the reactions in Eqs. (15)-(18), and hence the electrochemical potential, showed that with an increase in temperature, formic acid formation became more unfavorable.4 In the case of formaldehyde, methanol, and methane formation, the calculation indicated a positive shift in the reduction potential, but of very small magnitude ca. 30 mV for a temperature change from 300 to 500 K, and ca. 20 mV from 500 to 1200 K.4... 

Halmann reported in 1978 the first example of the reduction of carbon dioxide at a p-GaP electrode in an aqueous solution (0.05 M phosphate buffer, pH 6.8).95 At -1.0 V versus SCE, the initial photocurrent under C02 was 6 mA/ cm2, decreasing to 1 mA/cm2 after 24 h, while the dark current was 0.1 mA/cm2. In contrast to the electrochemical reduction of C02 on metal electrodes, formic acid, which is a main product at metal electrodes, was further reduced to formaldehyde and methanol at an illuminated p-GaP. Analysis of the solution after photoassisted electrolysis for 18 and 90 h showed that the products were 1.2 x 10-2 and 5 x 10 2 M formic acid, 3.2 x 10 4 and 2.8 x 10-4 M formaldehyde, and 1.1 x 10-4 and 8.1xlO 4M methanol, respectively. The maximum optical conversion efficiency calculated from Eq. (23) for production of formaldehyde and methanol (assuming 100% current efficiency) was 5.6 and 3.6%, respectively, where the bias voltage against a carbon anode was -0.8 to -0.9 V and 365-nm monochromatic light was used. In a later publication,4 these values were given as ca. 1% or less, where actual current efficiencies were taken into account [Eq. (24)]. 

In has been observed in the case of electroless Cu-Pd deposition from electroless solutions containing formaldehyde as reductant, that codeposition of small amounts of Pd with Cu results in appreciable reduction in the amount of H2 gas evolved [50], For example, codeposition of 0.3 at% Pd yields a reduction of 30% in the amount of evolved H2. It is difficult, however, to formulate stable electroless solutions involving Pd2+ since it has strong tendency in the electroless solution to become reduced due to it relatively high electrochemical series potential (ca. 0.95 V vs. RHE3). 

The same authors proposed a complex system for the electrochemically driven enzymatic reduction of carbon dioxide to form methanol. In this case, methyl viologen or the cofactor PQQ were used as mediators for the electroenzymatic reduction of carbon dioxide to formic acid catalyzed by formate dehydrogenase followed by the electrochemically driven enzymatic reduction of formate to methanol catalyzed by a PQQ-dependent alcohol dehydrogenase. With methyl viologen as mediator, the reaction goes through the intermediate formation of formaldehyde while with PQQ, methanol is formed directly [77],... 

Fuel cells using directly liquid fuels are advantageous in this aspect. Methanol, formaldehyde (water solution), formic acid (water solution) and hydrazine are among fuels relatively easy to oxidize electrochemically. Alcohol and hydrocarbon with larger molecular weight are much harder to oxidize completely to C02- Other qualifications to be considered are price, availability, safety, energy density and ease of handling. 

For example, in electroless deposition of copper, when the reducing agent is formaldehyde and the snbstrate is Cu, Hads desorbs in the chemical reaction (8.17). If the substrate is Pd or Pt, hydrogen desorbs in the electrochemical reaction (8.18). 

The most studied anodic partial reaction is the oxidation of formaldehyde. Red = H2CO. The overall reaction of the electrochemical oxidation of formaldehyde at the copper electrode in an alkaline solution proceeds as... 

The value of the transfer coefficient a is usually 0.50. In the electrochemical oxidation of an organic molecule the transfer coefficient a may be considerably less than 0.50. One example is the oxidation of formaldehyde in electroless deposition of copper. 

Other electrochemical processes of organic compounds on Pb electrodes or electrodes with UPD Pb have been studied - formaldehyde [323], oxalic acid [386], trichloro- and trifluoroethane [387], 1-phenylethylamine [388], 3-hydroxychi-nuclidine [388], dichlorodifluoromethane [389], polychlorobenzenes [390], 1-propa-nol [391], pyrrole polymerization [392], and inorganic compounds - phosphine [388] and sulfate(IV) ions [393]. Simultaneous catalytic or inhibiting influence of organic solvents - acetonitrile, dimethyl-sulfoxide, and Pb + presence on electrooxidation of small organic molecules on Pt electrodes has been studied using on-line mass spectroscopy [394],... 

The resorcinol-formaldehyde polymers have been used to prepare highly porous carbon materials, by controlled pyrolysis in an inert atmosphere [144,154], The microstructure of the carbon is an exact copy of the porous polymer precursor. Poly(methacrylonitrile) (PM AN) PolyHIPE polymers have also been used for this purpose. These monolithic, highly porous carbons are potentially useful in electrochemical applications, particularly re-chargeable batteries and super-capacitors. The RF materials, with their very high surface areas, are particularly attractive for the latter systems. 

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