Adsorption/reduction reactions of trichloroethylene by elemental iron in the gas phase: The role of water

The interactions of TCE with "clean" and "partially oxidized" Fe-0 were inv estigated in the gas phase. The removal of TCE from the gas phase proceeded by adsorption onto the Fe-0 surface or by dechlorination reactions with Fe O depending on the moisture content of the reaction medium. Unlike the aque ous phase, water was a critical variable competing with TCE for adsorption sites a nd, above a critical limit, serving as a proton donor for the hydro genolysis of TCE. The adsorption of water (relative humidity, RH = 6-97%) w as fit to a multilayer BET isotherm. The extent of water adsorption was nea rly identical for both forms of FeO on a surface area basis, i.e., mol/m(2) . The adsorption of TCE decreased by more than 1 order of magnitude from 6% to 10% RH, after which a more stable region (<50% decrease between 20% and 97% RH) appeared above monolayer water coverage (<similar to>26% RH). The removal of TCE from the gas phase was strictly by adsorption up to a "criti cal" RH, i.e., 72% for acid-washed and 92% for the partially oxidized surfa ces, above which dechlorination occurred and the hydrogenolysis byproducts appeared.