- Characterizing Cation Chemistry for Anion Exchange Membranes - A Product Study of Benzylimidazolium Salt Decompositions in the Base
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Imidazolium functionality has played a prominent role in research on anion exchange membranes for use in alkaline electrochemical devices. Base stability and degradation of these materials has been much studied, but in many instances, product pathways have not been thoroughly delineated. We report an NMR study of base-induced decomposition products from three benzylimidazolium salts bearing varying extents of methyl substitution on the imidazolium ring. The major products are consistent with a hydrolytic ring fragmentation pathway as the principal mode of decomposition. We observe several new products not previously reported in the literature on imidazolium salt degradation, including benzilic acid rearrangement products formally derived from intermediate 1,2-dicarbonyl compounds or their equivalents. However, the overall reactions are complex, the yields of observed products do not account for all consumed starting materials, and mechanistic ambiguities remain.
- Pellerite, Mark J.,Kaplun, Marina M.,Webb, Robert J.
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- Hydrogen and chemicals from alcohols through electrochemical reforming by Pd-CeO2/C electrocatalyst
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The development of low-cost and sustainable hydrogen production is of primary importance for a future transition to sustainable energy. In this work, the selective and simultaneous production of pure hydrogen and chemicals from renewable alcohols is achieved using an anion exchange membrane electrolysis cell (electrochemical reforming) employing a nanostructured Pd-CeO2/C anode. The catalyst exhibits high activity for alcohol electrooxidation (e.g. 474 mA cm?2 with EtOH at 60 °C) and the electrolysis cell produces high volumes of hydrogen (1.73 l min?1 m?2) at low electrical energy input (Ecost = 6 kWh kgH2?1 with formate as substrate). A complete analysis of the alcohol oxidation products from several alcohols (methanol, ethanol, 1,2-propandiol, ethylene glycol, glycerol and 1,4-butanediol) shows high selectivity in the formation of valuable chemicals such as acetate from ethanol (100%) and lactate from 1,2-propandiol (84%). Importantly for industrial application, in batch experiments the Pd-CeO2/C catalyst achieves conversion efficiencies above 80% for both formate and methanol, and 95% for ethanol.
- Bellini, Marco,Pagliaro, Maria V.,Marchionni, Andrea,Filippi, Jonathan,Miller, Hamish A.,Bevilacqua, Manuela,Lavacchi, Alessandro,Oberhauser, Werner,Mahmoudian, Jafar,Innocenti, Massimo,Fornasiero, Paolo,Vizza, Francesco
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- Room temperature, near-quantitative conversion of glucose into formic acid
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Herein, a facile and efficient method was developed to selectively transform glucose into formic acid at room temperature. After parameter optimization, formic acid was obtained in an unprecedented 91.3% yield with a reaction time of 8 h in lithium hydroxide aqueous solution with hydrogen peroxide as the oxidant. The synergistic effects of the base and the oxidant promoted the glucose conversion at room temperature and enhanced the selectivity towards FA. Besides, the employed mild conditions have suppressed FA decomposition that often occurred under harsh conditions, which further improved the FA selectivity. A series of model compound tests were conducted to probe the possible intermediates based on which a plausible reaction pathway was proposed. In addition, the process is applicable to various carbohydrates such as cellobiose, starch, xylan, etc. This work opens up a simple, mild but effective method to produce FA from renewable biomass resources, which would remarkably alleviate the energy consumption, capital costs, handling risks, etc.
- Wang, Can,Chen, Xi,Qi, Man,Wu, Jianeng,G?zaydin, G?kalp,Yan, Ning,Zhong, Heng,Jin, Fangming
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p. 6089 - 6096
(2019/11/20)
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- Glycerol electrooxidation in alkaline medium using Pd/c, Au/c and Pdau/c electrocatalysts prepared by electron beam irradiation
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Pd/C, Au/C and PdAu/C electrocatalysts with different atomic ratios prepared using electron beam irradiation were tested for glycerol electrooxidation in single alkaline direct glycerol fuel cell (ADGFC). X-ray diffractograms (XRD) of PdAu/C electrocataly
- Geraldes, Adriana N.,Silva, Dionisio F.,Silva, Ju?lio C.M.,Souza, Rodrigo F.B.,Spinace?, Estevam V.,Neto, Almir O.,Linardi, Marcelo,Santos, Mauro C.
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p. 831 - 840
(2014/06/24)
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- Synthesis of α-amino and α-hydroxy acids under volcanic conditions: implications for the origin of life
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Facile synthesis of α-hydroxy and α-amino acids is observed at temperatures from 145 to 280 °C with catalytic Ni2+, with cyano ligands as source for C and N, and with CO as a reductant and as a source for C. Implications for the problem of the origin of life are discussed.
- Huber, Claudia,Eisenreich, Wolfgang,W?chtersh?user, Günter
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p. 1069 - 1071
(2010/04/05)
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- Kinetics and Mechanism of the Multi-step Oxidation of Ethylenediaminetetraacetate by - in Alkaline Media
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Alkaline solutions of - oxidise ethylenediaminetetraacetate (edta) in a multistep sequence which produces iminodiacetate (ida), glycinate and glycolate ions, and eventually ammonia, formaldehyde, carbon dioxide and water.The reaction shows changing stoichiometry and product distribution.At 0/->0 = 1:1, glycinate and ida are produced in similar amounts with detectable ammonia and formadehyde.When 0/->0 = 200:1, very little glycinate is produced with no ammonia or formadehyde detected.The kinetics of the oxidation was studied by the stopped-flow method at high excesses of edta and 25 deg C and I = 1.2 mol dm-3.The overall rate is as in eqauation (i) obs = ((A+B->)4->)/(-> + C4->)> (i), where the coefficients, obtained by non-linear least-square analysis, are A = 4.38 +/- 0.57 s-1, B = 34.8 +/- 1.1 dm3 mol-1 s-1 and C = 26.3 +/- 2.1.A multi-step electron-transfer mechanism is proposed involving initial C-N bond cleavage at the ethylenediamine group.
- Sun, Yunfu,Kirschenbaum, Louis J.,Kouadio, Issifou
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p. 2311 - 2316
(2007/10/02)
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- Gas phase acidities of aliphatic carboxylic acids, based on measurements of proton transfer equilibria
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Measurements of the gas phase proton transfer equilibrium : AH + B- = A- + BH with a pulsed electron high pressure mass spectrometer (PHPMS) lead to ΔG01 and ΔH01 data.These relative acidities are converted to the absolute acidities : AH = A- + H+ by calibration of the relative ΔG01 and ΔH01 scale to the known values for ΔG01 and ΔH01 of a reference compound (HCl).Earlier determinations that included 16 aliphatic AH are extended in the present work and provide data for 47 aliphatic carboxylic acids.These include halogen, OH, CH3O, C2H5O, PhO, and NH2 substituted acetic acids, and halogen substituted, unsaturated, and cyclic RCO2H of higher carbon number.The effects of the various substituents on the gas phase acidity are briefly examined.Key words: acidities in gas phase, proton transfer equilibria, ion-molecule equilibria, mass spectrometry.
- Caldwell, Gary,Renneboog, Richard,Kebarle, Paul
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p. 611 - 618
(2007/10/02)
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- Halogenation of Acetone. A Method for Determining pKas of Ketones in Aqueous Solution, with an Examination of the Thermodynamics and Kinetics of Alkaline Halogenation and a Discussion of the Best Value for the Rate Constant for a "Diffusion-Controlled Reaction". Energetic ...
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The pKa of a simple ketone can be determined by analysis of the kinetics of halogenation in alkaline solution (J.Am.Chem.Soc. 1982, 104, 895).Details of the determination of the pKa of acetone are reported.The stoichiometry of chlorination of acetone is 2.15 hypohalites per acetone; bromination consumes 2.83 hypobromites.The major product from chlorination is lactate and not acetate; lactate is a minor product from bromination of acetone.The kinetic significance of the possible side reactions is discussed.The determination of the pKa requires knowledge of the rate constant for a diffusion-controlled reactionof nonspherically symmetrical molecules in water; the state of our knowledge of this rate constant is reviewed critically.It is shown that for reactions involving diffusion together of reactants which then undergo direct heavy-atom bond making it is very unusual for the diffusion limit to be reached, although the observed rate constant may become insensitive to the thermodynamic rectivity of the reactants.
- Guthrie, J. Peter,Cossar, John,Klym, Alex
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p. 1351 - 1360
(2007/10/02)
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