Methanol, properties poisoning

Platinum is the only acceptable electrocatalyst for most of the primary intermediate steps in the electrooxidation of methanol. It allows the dissociation of the methanol molecule hy breaking the C-H bonds during the adsorption steps. However, as seen earlier, this dissociation leads spontaneously to the formation of CO, which is due to its strong adsorption on Pt this species is a catalyst poison for the subsequent steps in the overall reaction of electrooxidation of CHjOH. The adsorption properties of the platinum surface must be modified to improve the kinetics of the overall reaction and hence to remove the poisoning species. Two different consequences can be envisaged from this modification prevention of the formation of the strongly adsorbed species, or increasing the kinetics of its oxidation. Such a modification will have an effect on the kinetics of steps (23) and (24) instead of step (21) in the first case and of step (26) in the second case. 

DMC is classified as a flammable liquid, smells like methanol, and does not have irritating or mutagenic effects, either by contact or inhalation. Therefore, it can be handled safely without the special precautions required for the poisonous and mutagenic methyl halides and DMS, and extremely toxic phosgene. Some physicochemical properties of DMC are listed in Table 4.2. 

On the other hand, drugs may inhibit the metabolism of other drugs. For example, allopurinol (a xanthine oxidase inhibitor that inhibits the synthesis of uric acid) increases the effectiveness of anticoagulants by inhibiting their metabolism. Chloramphenicol (a potent inhibitor of microsomal protein synthesis) and cimetidine (an H2-receptor blocker used in acid-pepsin disease) have similar properties. In addition, drugs may compete with each other in metabolic reactions. In methyl alcohol (methanol) poisoning, ethyl alcohol may be given intravenously to avert methanol-induced blindness and minimize the severe acidosis. Ethyl alcohol competes with methyl alcohol for... 

The toxic properties of methanol are the result of accumulation of the formate intermediate in the blood and tissues of exposed individuals. Formate accumulation produces metabolic acidosis leading to the characteristic ocular toxicity (blindness) observed in human methanol poisonings. 

Pt has the highest adsorption of methanol on its surface, but its catalytic properties are low due to the formation of poison species (most notably CO) that can be oxidized only after the Pt is covered with OH. Platinum-based bimetallic electrocatalysts, such as Pt-Ru alloys and Ru-decorated Pt materials, are the most active ones. The bi-functional mechanism is to a large extent operative in these catalysts. Most commercial Pt-Ru catalysts are based on 1 1 Pt-Ru alloy. While the alloys typically show enhanced activity in comparison with pure Pt, there is significant Pt loading in the bulk of the alloy in which catalysis does not proceed because the sites are inaccessible for methanol adsorption hence, the need for reducing the Pt content. 

Almost half of this methanol is converted to formaldehyde as a starting material for various resins and plastics. Methanol is also used as a solvent, as an antifreeze, and as a convenient clean-burning liquid fuel. This last property makes it a candidate as a fuel for automobiles— methanol is already used to power Indianapolis-class race cars— but extensive emissions tests remain to be done before it can be approved as a gasoline substitute. Methanol is a colorless liquid, boiling at 65°C, and is miscible with water in all proportions. It is poisonous drinking as little as 30 mL has been fatal. Ingestion of sublethal amounts can lead to blindness. 

The oxygen atom in methanol molecules makes methanol s properties very different than methane s. Methane is a colorless, odorless, and tasteless gas. Methanol, or wood alcohol, is a liquid with a distinct odor, and is poisonous in very small quantities. 

The major drawback of these lanthanide-copper alloys is that they are irreversibly poisoned by low concentrations of carbon dioxide, as already indicated above (Owen et al. 1987). The same authors also found that ZrCu2 and TiCu2 produced catalysts which were active for methanol synthesis, but difficult to activate. In a subsequent paper Owen et al. (1990) studied ternary lanthanide-Zr(or Ti)-Cu alloys with the hope that the addition of the larger lanthanide atom could increase the possibility of hydride formation and therefore the overall properties of these Zr(Ti)-Cu alloys. They prepared a series of... 

The inhibition can occur through either an electronic or a third-body effect. The presence of small amounts of Bi or As is able to modify the electronic properties of Pt(lll) in such a way that the spontaneous dissociation of formic acid is almost completely inhibited. It has also been estimated that the modification of the electronic properties by Bi adatoms that leads to the inhibition of formic acid dissociation extends over a distance of approximately seven Pt atoms. In contrast to this, the modification of electronic properties has no effect on the poison formation from methanol since the inhibition observed can be ascribed to a simple third-body mechanism. 

In order to improve the electrocatalytic properties of methanol electrodes, and to reduce the poisoning phenomenon usually observed with bulk platinum, different platinum based alloys were considered such as Pt-Ru, and Pt-Sn, etc. [153]. Therefore such alloys were also dispersed into electron conducting polymers. Hable et al. [53] were apparently the first authors to disperse Pt-Sn catalyst particles in a polyaniline matrix, in order to activate the oxidation of methanol. They evaluated the Pt/Sn ratio by X-ray Photoelectron Spectroscopy and found that small amounts of Sn (e.g. Pt/Sn ratios of 10/1) were sufficient to enhance the electrocatalytic oxidation of methanol. Pt was found to be in the Pt(0) state whereas Sn was in an oxidized form. Similar observations concerning the enhanced electrocatalytic activity of Pt-Sn particles incorporated in PAni films were made by Laborde et al. [154]. Such Pt-Sn alloys are also very active for the electrocatalytic oxidation of ethanol [68,154]. 

Properties Colorless clear volatile llq. sweet alcohol odor sol. In water, methanol, diethyl ether, chloroform, acetone m.w. 46.08 sp.gr. 0.789 (20 C) m.p. -114 C b.p. 78 C flash pt. (CC) 13 C Toxicology TLV 1000 ppm In air potentially poisonous by Ingestion Precaution Flamm. llq. fire hazard mod. explosion hazard NFPA , Flammability 3, Reactivity 0 Storage Hygroscopic... 

Properties Colorless liq. char, sweet odor sol. in methanol, toluene, water misc. with acetone, toluene, octane m.w. 114.15 dens. 0.9698 (20 C) f.p. -100 C b.p. 50-52 C flash pt. (OC) 57 C ref. index 1.434 Toxicotogy ACGIH TLV/TWA5 ppm STEL10 ppm (skin) LD50 (oral, rat) 922 mg/kg, (dermal, rabbit) 2550 mg/kg poison by ingestion moderately toxic by Inhalation and skin contact strong skin and eye Irritant can cause CNS depression, pulmonary edema may cause cancer mutation data TSCA listed... 

Properties Wh. solid beads or pellets absorbs water and CO2 from air sol. in water, alcohol, methanol, glycerin m.w. 40.00 dens. 2.12 (20/4 C) vapor pressure 1 mm (739 C) m.p. 318 C b.p. 1390 C Toxicolo ACGIH TLV/CL 2 mg/m of air LD50 (IP, mouse) 40 mg/kg LDLo (oral, rabbit) 500 mg/kg poison by IP route mod. toxic by ing. corrosive irritant to eyes, skin, mucous membrane mists and dusts cause small bums inh. can damage upper respiratory tract and lungs mutagenic data TSCA listed... 

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