Hydrodechlorination of Chlorinated Ethanes by Nanoscale Pd/Fe Bimetallic Particles

Abstract

Chlorinated ethanes are contaminants commonly found in soil and groundwater. The potential of nanoscale bimetallic (Fe∕Pd) particles for the hydrodechlorination of seven chlorinated ethanes (C2H6−xClx) was evaluated in batch experiments. Hexachloroethane (HCA) (C2Cl6), pentachloroethane (PCA) (C2HCl5), 1,1,2,2-tetrachloroethane (1,1,2,2-TeCA, C2H2Cl4), and 1,1,1,2-tetrachlorethane (1,1,1,2-TeCA, C2H2Cl4) were rapidly hydrodechlorinated (9–28 min half-lives) at a nanoparticle loading of 5 g/L. End products were ethane (61–87%) and ethylene (6–16%). Only one chlorinated intermediate, a corresponding β-elimination product, appeared temporarily during the reactions. Reductive dechlorination of 1,1,1-trichloroethane (1,1,1-TCA, C2H3Cl3) to ethane was completed at a relatively slower rate with half-life at 44.9 min. Little reduction of dichloroethane (C2H4Cl2) was observed within 24 h. The Pd/Fe bimetallic nanoparticles generally exhibit much higher reactivity when compared with conventional micro- and millimeter scale iron powders. The hydrodechlorination reactions are more complete, with a much higher yield of ethane and lower yield of chlorinated byproducts. A kinetic model incorporating a transition state species was proposed. Results from this work suggest that the Pd/Fe bimetallic nanoparticles may represent a treatment alternative for in situ remediation of chlorinated ethanes.