Ethanol oxidation reaction

There are two ways to produce acetaldehyde from ethanol oxidation and dehydrogenation. Oxidation of ethanol to acetaldehyde is carried out ia the vapor phase over a silver or copper catalyst (305). Conversion is slightly over 80% per pass at reaction temperatures of 450—500°C with air as an oxidant. Chloroplatinic acid selectively cataly2es the Uquid-phase oxidation of ethanol to acetaldehyde giving yields exceeding 95%. The reaction takes place ia the absence of free oxygen at 80°C and at atmospheric pressure (306). The kinetics of the vapor and Uquid-phase oxidation of ethanol have been described ia the Uterature (307,308). 

Poisoning of platinum fuel cell catalysts by CO is undoubtedly one of the most severe problems in fuel cell anode catalysis. As shown in Fig. 6.1, CO is a strongly bonded intermediate in methanol (and ethanol) oxidation. It is also a side product in the reformation of hydrocarbons to hydrogen and carbon dioxide, and as such blocks platinum sites for hydrogen oxidation. Not surprisingly, CO electrooxidation is one of the most intensively smdied electrocatalytic reactions, and there is a continued search for CO-tolerant anode materials that are able to either bind CO weakly but still oxidize hydrogen, or that oxidize CO at significantly reduced overpotential. 

Another metal that has attracted interest for use as electrode material is rhodium, inspired by its high activity in the catalytic oxidation of CO in automotive catalysis. It is found that Rh is a far less active catalyst for the ethanol electro-oxidation reaction than Pt [de Souza et al., 2002 Leung et al., 1989]. Similar to ethanol oxidation on Pt, the main reactions products were CO2, acetaldehyde, and acetic acid. Rh, however, presents a significant better CO2 yield relative to the C2 compounds than Pt, indicating a... 

THERMODYNAMICS AND KINETICS OF REACTIONS IN A DAFC ETHANOL OXIDATION... 

Leger JM, Rousseau S, Coutanceau C, Hahn E, Lamy C. 2(X)5. How bimetallic electrocatalysts does work for reactions involved in fuel cells Example of ethanol oxidation and comparison to methanol. Electrochim Acta 50 5118-5125. 

Figure 8.2 Reaction mechanism for ethanol oxidation on an Mo dimer/Si02 catalyst as an example of the reaction mode (a) in Figure 8.1...

The mechanism of ethanol oxidation is less well established, but it apparently involves two mechanistic pathways of approximately equal importance that lead to acetaldehyde and ethene as major intermediate species. Although in flow-reactor studies [45] acetaldehyde appears earlier in the reaction than does ethene, both species are assumed to form directly from ethanol. Studies of acetaldehyde oxidation [52] do not indicate any direct mechanism for the formation of ethene from acetaldehyde. 

Reactions alcohols, 29 36-49 adsorption, 29 36-37 clean surfaces, 29 37-38 ethanol oxidation, 29 44—48 methanol oxidation, 29 38-44 oxidation on copper and silver, 29 38-48 oxidation reaction, silver, 29 48-49 base-catalyzed, of hydrocarbons, 12 117 free radical mechanism in, of hydrogen peroxide, 4 343... 

Kometani et al. [71] reported that baker s yeast catalyzed the asymmetric reduction of acetol to (i )-1,2-propanediol with ethanol as the energy source. The enzyme involved in the reaction was an NADH-dependent reductase, and NADH required for the reduction was supplied by ethanol oxidizing enzyme(s) in the yeast. When washed cells of baker s yeast were incubated with 10 mg ml of acetol in an ethanol solution with aeration, (k)-1,2-propanediol was formed almost stoichiometrically with an optical purity of 98.2% e. e. 

The final reactions to be considered in the metabolism of ethanol in the liver are those involved in reoxidation of cytosolic NADH and in the reduction of NADP. The latter is achieved by the pentose phosphate pathway which has a high capacity in the liver (Chapter 6). The cytosolic NADH is reoxidised mainly by the mitochondrial electron transfer system, which means that substrate shuttles must be used to transport the hydrogen atoms into the mitochondria. The malate/aspartate is the main shuttle involved. Under some conditions, the rate of transfer of hydrogen atoms by the shuttle is less than the rate of NADH generation so that the redox state in the cytosolic compartment of the liver becomes highly reduced and the concentration of NAD severely decreased. This limits the rate of ethanol oxidation by alcohol dehydrogenase. 

Selected entries from Methods in Enzymology [vol, page(s)] Activity in ethanol oxidation, 233, 118 in hydroxyethyl radical formation analysis with reconstituted vesicles, 233, 127 characterization, 233, 123-125 monooxygenase activity, 231, 574-575 reductase [hemoglobin-catalyzed reactions with, 231, 573-574 oxygen concentration and, 231, 579 pH dependence, 231, 580 reaction mixtures, 231, 578 oxygen content, measurement, 231, 587-588 reductase concentration and, 231, 580 time dependence, 231, 578 preparation, 231, 577]. 

The generation of hydrogen from ethanol via catalytic autothermal partial oxidation (Equation 6.18) has been performed at temperatures of 430-730 °C using catalytic systems based on noble metals [202, 203]. Ethanol oxidation follows a very complex pathway, including several reaction intermediates formed and decomposed on both the supports and active metals that integrate the catalytic systems [204, 205]. 

Promotion and deactivation of unsupported and alumina-supported platinum catalysts were studied in the selective oxidation of 1-phenyl-ethanol to acetophenone, as a model reaction. The oxidation was performed with atmospheric air in an aqueous alkaline solution. The oxidation state of the catalyst was followed by measuring the open circuit potential of the slurry during reaction. It is proposed that the primary reason for deactivation is the destructive adsorption of alcohol substrate on the platinum surface at the very beginning of the reaction, leading to irreversibly adsorbed species. Over-oxidation of Pt active sites occurs after a substantial reduction in the number of free sites. Deactivation could be efficiently suppressed by partial blocking of surface platinum atoms with a submonolayer of bismuth promoter. At optimum Bi/Ptj ratio the yield increased from 18 to 99 %. 

Reactions of anthocyanins and flavanols take place much faster in the presence of acetaldehyde that is present in wine as a result of yeast metabolism and can also be produced through ethanol oxidation, especially in the presence of phenolic compounds, or introduced by addition of spirit in Port wine technology. The third mechanism proposed involves nucleophilic addition of the flavanol onto protonated acetaldehyde, followed by protonation and dehydration of the resulting adduct and nucleophilic addition of a second flavonoid onto the carbocation thus formed. The resulting products are anthocyanin flavanol adducts in which the flavonoid units are linked in C6 or C8 position through a methyl-methine bond, often incorrectly called ethyl-link in the literature. 

The reaction pathway, reactivity of the active sites, and the nature of adsorbed intermediates constitute the catalytic reaction mechanism. Our study has been focused on the investigation of the nature of adsorbed intermediates under reaction conditions. We report the results of in situ infrared study of CO and ethanol oxidation on Au/Ti02 catalysts. This study revealed the high activity of Au/Ti02 is related to the presence of reduced Au and oxidized Au sites which may promote the formation of carbonate/carboxylate intermediates during CO oxidation. 

Consequently, under these conditions, ethanol may be totally oxidized to carbon dioxide via the first reaction, partially oxidized to acetaldehyde via the second reaction, dehydrogenized... 

Propanol oxidation under mild conditions takes place with high selectivity. No products other than acetone were observed in the ATR spectra recorded in situ. The situation is more complex for the oxidation of primary alcohols such as ethanol. The first oxidation step produces acetaldehyde, which is prone to further reactions, as is apparent in the ATR spectra. Figure 20, left, shows ATR spectra recorded in situ during ethanol oxidation. Figure 20, right, shows some signals as a function of time. The experiment was performed in a manner similar to that of the one... 

A major group of photochemical reduction reactions are oxidation-reduction processes. As typical examples, phenazine (CXXI) and alloxan (CXXIII) are reduced by ethanol to give dihydrophenazine (CXXIl)/ 2 and alloxantin (CXXIV).42 Isatin (CXXV) in the presence of ace-naphthene (CXXVI) is reduced to isatide (CXXVII).204 The photoreaction proceeds at the expense of the alcohol, or (CXXVI) acetaldehyde and acenaphthylene (CXXVIII), are formed as by-products respectively. The formation of CXXVII may be due to the interaction of CXXV with the intermediate oxindole (CXXIX). 

The oxidation reactions are summarized in Reaction 1. In the following discussion the methanol-oxidized, ethanol-oxidized, and benzene-oxidized species will be referred to respectively as 2, 3, and 4. 

Oyama and Somorjai have studied the oxidation of ethanol and ethane over vanadia supported on silica.33 Ethane oxidation yielded ethylene and acetylene with considerable CO2 for highly dispersed catalysts. Ethanol oxidation to acetaldehyde, on the other hand was shown to be structure insensitive. Conversions and selectivities for reaction of ethanol are shown in Table III.33... 

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