Alternative sources of hydrogen for hydrodechlorination of chlorinated organic compounds in water on Pd catalysts

Formic acid, isopropanol and hydrazine were investigated as reductants for the Pd-catalyzed hydrodechlorination of chlorobenzene in water at ambient temperature. The intention was to find alternatives to molecular hydrogen with high water solubilities. Formic acid was found to be as reactive as H-2 under acidic and neutral conditions, but less reactive under alkaline conditions. The observed kinetics imply two pH-controlled reaction mechanisms (possibly H-atom and hydride transfer). H-consumers, such as chlorinated compounds, strongly stimulate the decomposition of formic acid. The half-life of 5 mg L-1 chlorobenzene in the presence of I mg L-1 Pd is about 2 min under optimal reaction conditions. Rh was found to be inactive in the formic acid driven hydrodechlorination. Isopropanol is less reactive by about five orders of magnitude than H-2. Hydrazine is effective as a H-donor for the hydrodechlorination under alkaline conditions. However, the reaction is slower than with H-2 by a factor of 30. From the technical and economic point of view, formic acid is a promising substitute for H-2. (C) 2004 Elsevier B.V. All rights reserved.