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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.

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.

The formation constants of the 1:1 and 1:2 complexes of Hg(II) with glutathione and their protonated species have been determined by using a competitive potentiometric titration with the competing ligand diethylenetriaminepentaacetic acid (DTPA). The formation constants of the 1:1 complex and its protonated species have not been reported previously. The formation constant of the 1:2 complex of Hg(II) and glutathione is substantially smaller than the accepted values that has been reported in the literature. These results have important implications in the models that have been employed to explain the mobilization and distribution of Hg(II) in biological systems.

Trichloroethene (TCE) was reduced with zero‐valence iron and palladized iron in zero‐head‐space extractors. Progress of the reaction in these batch studies was monitored with purge‐and‐trap gas chromatography and a flame ionization detector. When a 5 ppm initial concentration of TCF. reacts with zero‐valence iron, approximately 140 ppb of vinyl chloride persists for as long as 73 days. The concentration of vinyl chloride (approximately If) ppb) remaining with palladized iron is approximately an order of magnitude less than when zero‐valence iron is the reductant. These data suggest that volatile byproducts may be under‐represented in oilier published data regarding reduction with zero‐valence metals. These results also demonstrate that the reduction of TCE with palladized iron (0.05 percent palladium) is more than an order of magnitude faster than with zero‐valence iron. Wilh a 5:1 solution‐to‐solid ratio the TCE half‐life with zero‐valence iron is 7.41 hours. but is only 0.59 hours with the palladized iron.

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