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HYDRODEHALOGENATION OF 1- TO 3-CARBON HALOGENATED ORGANIC COMPOUNDS IN WATER USING A PALLADIUM CATALYST AND HYDROGEN GAS. (R825421)
Citation:
Lowry, G. AND M. Reinhard. HYDRODEHALOGENATION OF 1- TO 3-CARBON HALOGENATED ORGANIC COMPOUNDS IN WATER USING A PALLADIUM CATALYST AND HYDROGEN GAS. (R825421). ENVIRONMENTAL SCIENCE & TECHNOLOGY. American Chemical Society, Washington, DC, 33:1905-1910, (1999).
Description:
Supported palladium (Pd) metal catalysts along with H2 gas show
significant potential as a technology which can provide rapid, on-site
destruction of halogenated groundwater contaminants. Pd catalyzes the rapid
hydrodehalogenation of nine 1- to 3-carbon HOCs, resulting in little or no
production of halogenated intermediates. Initial transformation rates were
compared for 12 HOCs using 1 w/w% Pd-on-Al2O3 (Pd/Al) and
metallic Pd catalysts in clean, aqueous batch systems at ambient pressure and
temperature. Half-lives of 4-6 min were observed for 5-100 src="/ncer/pubs/images/mgr.gif">M (1-10 mg/L) aqueous concentrations of PCE,
TCE, cis-, trans-, 1,1-DCE, carbon tetrachloride, and
1,2-dibromo-3-chloropropane at ambient temperature and pressure with 0.22 g/L of
catalyst. Using Pd/Al, TCE transformed quantitatively (97%) to ethane without
formation of any detectable chlorinated intermediate compounds. This implies a
direct conversion of TCE to ethane at the Pd surface. Carbon tetrachloride
transformed primarily to methane and ethane and minor amounts of ethylene,
propane, and propylene. Chloroform is a reactive intermediate (20%). Formation
of C2 and C3 products implies a free radical mechanism. Methylene chloride,
1,1-dichloroethane, and 1,2-dichloroethane were nonreactive. Reaction mechanisms
and kinetic models are postulated for TCE, carbon tetrachloride, and chloroform
transformation.