LOW-TEMPERATURE DECOMPOSITION OF SOME HALOGENATED HYDROCARBONS USING METAL-OXIDE POROUS CARBON CATALYSTS

Catalysts comprising metal oxides dispersed on porous carbon supports are shown to be very effective in the decomposition of halogenated hydrocarbons by air at and below 250-degrees-C. A wide range of substrates, including methylene chloride, 1,2-dichloroethane, 1,2,4-trichlorobenzene, tetrachloroethylene, 1,1,2,2-tetrachloroethane, and carbon tetrachloride, are converted selectively to CO2, CO, and HCl. The carbon supports also show significant activity in the absence of metal species. Trends in reactivity with catalyst variation suggest that the carbon micropore content and acidity are determining factors in the catalytic activity. Mechanistic studies with a porous, highly active CrO3/Ambersorb1 (Ambersorb is a registered trademark of the Rohm and Haas Company) resin illustrate that the components operate through two discrete pathways: the carbon functions oxidatively as a catalytic agent itself while the chromium species functions to decompose the chlorinated hydrocarbon anaerobically. Kinetic studies of methylene chloride decomposition over an undoped Ambersorb resin show a first-order dependence on CH2Cl2 concentration and an activation energy of 11.0 kcal/mol. In further examination of the catalytic decomposition process, it was found that a source of hydrogen, either as a component of the chlorinated hydrocarbon or as an added reagent, is necessary to regenerate the catalyst. Water was found to serve this function but not to saturate the active site for adsorption and destruction of the organic reactant. This finding gives the carbon catalysts a clear advantage over zeolite based catalysts for aqueous hazardous waste remediation processes.1