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We have hypothesized that hydrogen gas intercalated in a palladium lattice is the powerful reducing agent that reductively dechlorinates chlorinated organic compounds that are adsorbed on the surface of palladized electrodes. We have shown that dechlorination of 4-chlorophenol to phenol occurs rapidly on palladized carbon cloth or pal ladized graphite electrodes. The reactions on the palladized carbon cloth and graphite depend on the adsorption of the chlorinated organic compound on the carbon surface and the reaction with hydrogen at the palladium/carbon interface. Palladium was much more effective in promoting the dechlorination reaction than platinum, probably because of its ability to intercalate hydrogen in its lattice.

Abstract-A review of pertinent equations and current research indicates that when gasoline oxygenated with methyl tert-butyl ether (MTBE) comes into contact with water, large amounts of MTBE can dissolve. At 25ЊC, the water solubility of MTBE is about 5,000 mg/L for a gasoline that is 10% MTBE by weight, whereas for a nonoxygenated gasoline, the total hydrocarbon solubility in water is typically about 120 mg/L. Methyl tert-butyl ether sorbs only weakly to subsurface solids; therefore, sorption does not substantially retard the transport of MTBE by ground water. In addition, MTBE generally resists biodegradation in ground water. The half-life of MTBE in the atmosphere can be as short as 3 d in a regional airshed. In the air, MTBE tends to partition into atmospheric water, including precipitation. However, the washing out of gas-phase MTBE by precipitation will not, by itself, greatly alter the gas-phase concentration of the compound in the air. The partitioning of MTBE to precipitation can nevertheless result in concentrations as high as 3 g/L or more in urban precipitation and can contribute to the presence of MTBE in surface and ground water.

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Palladized iron (Pd/Fe) has been successfully used for the rapid dechlorination of organic environmental contaminants in aqueous solutions. We have investigated the nature of the Pd/Fe surface by X-ray photoelectron spectroscopy. Our results indicate that the reactive Pd/Fe surface is formed by the stepwise reduction of Pd(IV) in solution to Pd(II), which replaces protons on the hydroxylated iron oxide surface and forms Pd(II)-O-Fe bonds. These bonds are unstable and collapse spontaneously to yield the reactive palladized iron in which the palladium is in the elemental state. Prolonged exposure of this Pd/Fe surface to a saturated solution of aqueous TCE results in the growth of the hydroxylated iron oxide film that deactivates the Pd/Fe surface. The thick hydroxylated iron oxide film can be removed, and the original activity of the Pd/Fe surface can be restored by washing the surface with a dilute acid solution.