Zero- and High-Pressure Mechanisms in the Complex Forming Reactions of OH with Methanol and Formaldehyde at Low Temperatures
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A recent ring polymer molecular dynamics study of the reactions of OH with methanol and formaldehyde at zero pressure and below 100 K has shown the formation of collision complexes with long lifetimes, longer than 100 ns for the lower temperatures studied, 20–100 K (del Mazo-Sevillano et al., 2019). These long lifetimes support the existence of multicollision events with the He buffer-gas atoms under experimental conditions, as suggested by several transition state theory studies of these reactions. In this work, we study these secondary collisions, as a dynamical approach to study pressure effects on these reactions. For this purpose, the potential energy surfaces of He with H2CO, OH, H2O, and HCO are calculated at highly accurate ab initio level. The stability of some of the complexes is studied using path integral molecular dynamics techniques, determining that OH–H2CO complexes can be formed up to 100 K or higher temperatures, whereas the weaker He–H2CO complexes dissociate at approximately 50 K. The predicted IR intensity spectra show new features which could help the identification of the OH–H2CO complex. Finally, the He–H2CO + OH and OH–H2CO + He collisions are studied using quasi-classical trajectories, finding that the cross section to produce HCO + H2O products increases with decreasing collision energy, and that it is ten times higher in the He–H2CO + OH case.Keywords:
Transition state
Transition state theory
Resorcinol
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Abstract A silver‐containing ceramics has been evaluated as a catalyst for oxidation of [ 11 C]methanol to [ 11 C]formaldehyde. 7.99 GBq of [ 11 C]carbon dioxide was reduced to [ 11 C]methanol which could be reoxidized to 1.73 GBq of [ 11 C]formaldehyde in 5 minutes (25%, decay corrected).
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Metastability
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Abstract A ceramic material, prepared from kaolin doped with silver ions in various concentrations, was evaluated as a catalyst for the conversion of [ 11 C] methanol into [ 11 C]formaldehyde in a gas flow system. Employment of [ 11 C] methanol with a minimized water content, 300 mg of catalyst (20% of silver) at 500°C and a carrier gas flow rate of 40 mL/min resulted in a radiochemical decay‐corrected [ 11 C]formaldehyde yield of 67% relative to [ 11 C]methanol. Wet [ 11 C]methanol under the same conditions gave 54% of [ 11 C] formaldehyde. Copyright © 2003 John Wiley & Sons, Ltd.
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Formaldehyde formed in the electrochemical oxidation of methanol was measured in order to assess its importance as a reaction intermediate and potential source of efficiency loss in direct methanol fuel cells. Formaldehyde generated from 15 mM methanol in 0.1 M HClO4 at fixed potentials with a small volume electrolysis arrangement was determined with a sensitive fluorescence assay. The formaldehyde yields approached 30% of the total electrolysis charge at 0.2−0.3 V (vs Ag/AgCl). The percentages dropped at more positive potentials, as other oxidation pathways became dominant. However, formaldehyde production continued to increase with potential, maximizing near 0.5 V. This study demonstrates that formaldehyde, which is often not detectable with modern in situ analysis techniques, can be produced during methanol electrochemical oxidation in significant amounts. A fluorescence assay specific for formaldehyde is suggested for use in parallel with in situ measurements.
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Abstract. The effect of various lower aliphatic aloohols on the accumulation of formaldehyde in rat liver homogenates incubated with methanol has been studied. The addition of ethanol inhibited very clearly the accumulation of formaldehyde, n‐propanol, isopropanol or n‐butanol had no effect on the accumulation of formaldehyde.
Propanol
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A detailed chemical kinetic model has been proposed to explain the formaldehyde formation in a methanol fueled spark ignition engine. In comparison of the calculated results with the experimental results from a reactor tube, the reactions NO+HO2=NO2+OH and NO2+H=NO+OH became important for methanol oxidation and formaldehyde formation in exhaust gases with a large amount of nitric oxide. Accordingly, N-series reactions should be included in this scheme. According to the calculated results, methanol decreases with an increase of the residence time. On the other hand, formaldehyde increases to maximum value and then slowly decreases. At temperatures in excess of 950 K, methanol and formaldehyde oxidations are rapid, and complete in the residence time of 20 milliseconds. At temperatures below 800 K, methanol oxidation is considerably slower and formaldehyde is accumulated by increasing the residence time. The agreement between experimental and calculated results indicates that this proposed scheme is reasonable for studying formaldehyde formation mechanism.
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