Carbon dioxide reduction reactions

Products and Standard Reduction Potentials of Carbon Dioxide Reduction Reactions, at pH 6.8, Involving 2-18 Electrons Standard Reduction Potential... 

Of great interest and importance are studies on carbon dioxide reduction on copper electrodes, performed primarily by Japanese scientists. Under certain conditions, formation of methane and ethylene with high faradaic yields (up to 90%) was observed. The efficiency and selectivity of this reaction depends very much on the purity and the state of the surface of the copper electrode. For this reason, many of the published results are contradictory. 

The mechanism of carbon dioxide reduction in aqueous and nonaqueous solutions was investigated by several authors. It is now generally accepted that the reduction of carbon dioxide to formate ions is a multistep reaction with the intermediate formation of free radicals CO2 and HCO2 either in the solution or adsorbed on the electrode ... 

The chemical processes occurring inside the blast furnace can be stated to start basically from the hot air coming into contact with the white-hot coke. The coke burns to form carbon dioxide. This reaction generates a very large quantity of heat, and it is this heat which maintains the high temperature necessary for the reduction process. As the gas is... 

From a fundamental viewpoint, carbon dioxide reduction is a model reaction which can help us to understand better the mechanism of natural photosynthesis.11 Development of artificial photosynthetic systems, by mimicking functions of green plants, is one of... 

Both CO and C02 are reduced by eh. The immediate product of the first reaction is CO-, which reacts with water, giving OH and the formyl radical the latter has been identified by pulse radiolysis. The product of carbon dioxide reduction, C02-, is stable in the condensed phase with an absorption at 260 nm. It reacts with various organic radicals in addition reactions, giving carboxylates with rates that are competitive with ion-ion or radical-radical combination rates. 

More complicated reactions that combine competition between first- and second-order reactions with ECE-DISP processes are treated in detail in Section 6.2.8. The results of these theoretical treatments are used to analyze the mechanism of carbon dioxide reduction (Section 2.5.4) and the question of Fl-atom transfer vs. electron + proton transfer (Section 2.5.5). A treatment very similar to the latter case has also been used to treat the preparative-scale results in electrochemically triggered SrnI substitution reactions (Section 2.5.6). From this large range of treated reaction schemes and experimental illustrations, one may address with little adaptation any type of reaction scheme that associates electrode electron transfers and homogeneous reactions. 

The one-carbon reactions and enzymes unique to the carbon dioxide reduction pathway are shown in Figure 11.2 and Table 11.2. Electrons required for the reductive reactions are derived from the oxidation of either hydrogen or formate, catalyzed by hydrogenase or formate dehydrogenase. 

The catalytic cycles for reduction of alkyl and atyl halides using Ni(o), Co(i) or Pd(o) species are interrupted by added carbon dioxide and reaction between the first formed carbon-metal bond and carbon dioxide yields an alkyl or aryl car-boxylate. These catalyses reactions have the advantage of occuriiig at lower cathode potentials than the direct processes summarised in Table 4.14. Mechanisms for the Ni(o) [240] and Pd(o) [241] catalysed processes have been established. Carbon dioxide inserts into the carbon-metal bond in an intermediate. Once the carboxy-late-metal species is formed, a further electron transfer step liberates the carboxy-late ion reforming the metallic complex catalyst. 

The overall reaction of carbon dioxide reduction in the Calvin-Benson cycle (Fig. 17-14) becomes... 

Carbon dioxide insertion reactions are potential intermediate steps in catalytic cycles leading to reduction of C02 or its incorporation into organic molecules. Analogies with carbon monoxide chemistry may be drawn, e.g., insertion reactions of carbon monoxide (20) play a key role in both the... 

In general the energy demands for the carbon dioxide reduction process decrease with the extent of retention of oxygen in the product molecules, e.g., reactions (3) and (4) are much less energy exhausting than is reaction (5). It is thus anticipated that in the short run the industrial utilization of... 

Oxidation-reduction reactions are ofter accompanied by release of heat and sometimes, flame. Combustion reactions are oxidation-reduction reactions that occur when oxygen oxidizes another material. For example, burning carbon in a lump of coal produces carbon dioxide. The reaction can be illustrated as ... 

Introduction. The reduction of the carboxyl group (COOH) to the carbonyl group (CO) can be brought about by the simultaneous oxidation of another carboxyl group to carbon dioxide. This reaction takes place when the barium or calcium salt of acids is subjected to distillation ... 

Sulphate reduction in marine sediments is often the dominant form of carbon remineralisation, and contributes most of the alkalinity observed in the sediment pore-water. When concentrations of sulphate fall below 35 to 40 pM, carbon dioxide reduction by methanogens may begin, whereas sulphate levels below about 30 pM are required before the onset of acetate-type reduction reactions that dominate methanogenesis (Kuivila et al., 1989). Carbon dioxide reduction is usually only evident in the sulphate reduction zone, where bicarbonate is produced, but it can contribute about 65% of the methane flux at its peak (Crill Martens, 1986). 

Use of Stoichiometric Reactions in the Design of Redox Catalyst for Carbon Dioxide Reduction... 

Carbon Dioxide Reduction with an Electric Field Assisted Hydrogen Insertion Reaction... 

Major limitation associated with carbon dioxide reduction is the accuracy of the analytical measurements employed. The photocatalytic process is a multielectron transfer process, hence the reaction leads to the formation of a variety of products like carbon monoxide, methane, higher hydrocarbons, alcohol, aldehydes, carboxylic acid etc., with some intermediates. The identification and quantification of the products are needed for the best selection of photocatalyst, comparison and elucidation of reaction mechanisms. Currently there is no standard analysis method that has been developed for product analysis of carbon dioxide reduction. Hence the results of these measurements also include the products derived from the carbon contamination invariably present in the reaction sys-... 

Since the carbon dioxide reduction is a complex process, the efficiency depends upon a number of factors such as electron migration through band gap, electron transfer reactions, adsorption of substrate on the semiconductor surface, surface reactions, nature of solvent medium, illumination source, reactor geometry and a number of other... 

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