Catalytic Degradation of Chlorinated Hydrocarbons by Fe-zeolite: Influence Factors and Degradation Mechanism

Chlorinated hydrocarbons are among the most common pollutants at industrial sites and have been detected widespreading in both soil and groundwater. Because of their environmental persistence and toxicities, there is a growing interest in developing new technologies for the removal of chlorinated hydrocarbons in the environment. The degradation of a typical chlorinated hydrocarbon, trichloroethane (TCE) by hydrogen peroxide (H₂O₂) was studied by using an iron-loaded zeolite (Fe-ZSM-5) as heterogeneous catalyst. In the Fe-ZSM-5/H₂O₂ system, the removal rate of TCE (0.9 mmol·L^-1) reached 88% with 0.8 g·L^-1 Fe-ZSM-5 and 10 mmol·L^-1 H₂O₂ at initial pH 7.4 and ambient temperature. And with the increasing of catalyst dosage and H₂O₂ concentration, the removal rate of TCE gradually increased, and the removal rate could reach up to 99%. In addition, initial pH had minor effect on the degradation of TCE. Compared with Fe-ZSM-5, the degradation rate of TCE was only 41% by ZSM-5 without iron loading, and the removal rate decreased when H₂O₂ concentration increased from 6 mmol·L^-1 to 14 mmol·L^-1, while the initial pH had also a minor effect on the removal rate of TCE. The results of free radical quenching experiment show that ·OH played a major role in the degradation of TCE in Fe-ZSM-5/H₂O₂ system, which was largely absent in ZSM-5/H₂O₂ system.