Methanol In Acidic Media Research Articles

Carbon–ceramic composites from coal tar pitch and clays: application as electrocatalyst support

Carbon–ceramic composites have been prepared and characterised by different techniques (electron microscopy, X-ray microanalysis, X-ray diffraction and cyclic voltammetry). The effect on the conductivity of the thermal treatment temperature of the composites and the structure of the starting ceramic has been analysed. The results demonstrate that the layered structure of the clay determines their conductivity. The composites prepared are conductors and the conductivity goes through a maximum with increasing thermal treatment. Platinum has been successfully deposited on the carbon–ceramic composite by chemical and electrochemical methods. A better distribution of platinum and smaller particle sizes are obtained by the electrochemical method. The direct electrooxidation of methanol in acid medium has been studied on platinum-modified carbon–ceramic electrodes.

On-line mass spectrometry investigation of the reduction of carbon dioxide in acidic media on polycrystalline Pt

Differential electrochemical mass spectrometry (DEMS) is used to investigate the reaction of electroreduction of CO 2 on platinum porous electrode in acidic media. This technique, which gives molecular specificity, permits the reaction products to be followed concurrently with potential and time. These results showed for the first time the on-line production of methanol in acidic media using a Pt electrodeposited electrode. Reduction of CO 2 in perchloric acid on Pt occurs in the H 2 evolution region leading to the formation of formic acid methanol and traces of methane. Experiments using CO show that this substance is the intermediate of the pathway leading to methanol.

Electrocatalytic oxidation of methanol on PPy electrode modified by gold using the cementation process

The preparation by the electrochemical cementation process of dispersed gold microparticles on polypyrrole (PPy) coatings on iron surface and their electrocatalytic activity towards methanol oxidation were studied. The reaction of cementation of gold onto Fe/PPy electrode was shown to be under chemical control with a high activation energy. These films were investigated by scanning electron microscopy (SEM), energy-dispersive X-ray analysis (EDX) and cyclic voltammetry. These dispersed Au microparticles exhibit higher electrocatalytic activity than a bare gold electrode towards the electrochemical oxidation of methanol in acidic media.

Platinum-tin alloy electrodes for direct methanol fuel cells

Pt electrodes, modified by partial electrodeposited tin, were used as anodes for the catalytic electrooxidation of methanol in acid medium. Sn was electrodeposited galvanostatically and potentiostatically. Cyclic voltammetry was used to study the methanol electrooxidation. Pt modified with Sn proved superior to pure platinum as shown from the methanol peak current densities. Sn also improved the performance regarding the stability of the anode over repeated cycles. It was found that electrodeposited Sn facilitates the oxidation of intermediate poison products through a mixed homogeneous–heterogeneous catalytic mechanism.

Direct electrooxidation of methanol on highly dispersed platinum-based catalyst electrodes: temperature effect

The direct electrooxidation of methanol in acid medium was studied on electrodes made of a perfluorinated membrane with small amounts of metal catalysts incorporated by chemical reduction. Platinum is a good electrocatalyst for this reaction, but needs to be modified by other metals in order to obtain oxidation potentials much more compatible with a working anode in a direct methanol fuel cell. Ruthenium and tin appear to give encouraging results, leading to a negative shift of more than 250 mV as compared to the potential obtained with pure platinum. Other parameters were investigated in this work, such as the working temperature, and the manner of introduction of the methanol into the cell. By gaseous supply, it was possible to carry out measurements at higher temperatures than with methanol in solution, and consequently to greatly improve the performance of the catalytic electrode.

Cyclic voltammetric and potential-modulated reflectance spectroscopic study of the electroadsorption of methanol and ethanol on a platinum electrode in acid and alkaline media

The electroadsorption of methanol and ethanol on smooth Pt, both in 0.5 M HCIO 4 and 1 M NaOH, has been studied by cyclic voltammetry (CV) and potential-modulated reflectance spectroscopy (PMRS). It has been found by CV, apparently for the first time, that the two alcohols physisorb on Pt, both in acid and alkaline media, provided the admission potential (the potential at which the alcohol is first admitted into the cell) is lower than 0.1–0.2 V, and that there is alcohol in solution, which means that the physisorption is reversible. The amount of chemisorbed species was determined by CV in the absence of alcohol in solution, using a flow cell. In the four cases (methanol and ethanol in both acid and base) the amount of CO produced by dissociative chemisorption changes little over a range of admission potentials, decreasing rapidly at lower and higher potentials. It has also been found by CV that, in agreement with the general opinion, with methanol in alkaline medium the only chemisorbed species is CO. On the contrary, with methanol in acid medium, and with ethanol in both acid and alkaline media, other species besides CO become chemisorbed on Pt. The PMR spectra of both methanol and ethanol on Pt in acid medium show a maximum at 270 nm, which we attribute to linearly adsorbed (on-top) CO.In basic medium, methanol shows a PMRS maximum at 280 nm, which has been assigned to bridge-bonded CO, while ethanol shows no PMRS maximum, although the amount of chemisorbed CO, as estimated from the CV obtained after refluxing with base electrolyte, is about the same as with methanol.

A new derivatization procedure for the analysis of hippuric acid and m-methyl-hippuric acid by gas chromatography

The industrial solvents, toluene and xylene, have physicochemical properties that can be hazardous to the workers exposed. Since hippuric acid and m-methyl-hippuric acid represent the products of toluene and xylene biotransformation in urine, they are used as biological markers in studies on occupational exposure to these solvents. Several methods have been used to determine hippuric acid and m-methyl-hippuric acid--either based on gas chromatography or on high-performance liquid chromatography. In this study we propose the derivatization of hippuric acid and methyl-hippuric acid using methanol in acid medium (HCl), a low-cost reagent with a low level of toxicity. The method has been routinely used in our laboratory for 1 year and has proven to be a reliable procedure for the biological control of occupational exposure to toluene and/or xylene.

L'effet d'anions sur l'oxydation anodique du méthanol

Anodic oxidation of methanol in acidic medium (1 N H2SO4) is briefly reviewed with the presentation of polarization and potentiodynamic curves. The possible mechanism of oxidation is presented: the inhibition phenomenon of oxidation is illustrated by the formation of oxides on the surface of platinum. The oxidation current of methanol is sometimes modified by the presence of anions in a low concentration (10−3 to 10−4 N). An attempt is made to relate the inhibitor effect of some anions to theoretical values of binding strength, crystal lattice energy, and heat of hydration. A succinct correlation can be set up between the importance of the inhibition effect and the classification of the anions in hard or soft bases.