Selective removal of chlorine from chloroaromatic pollutants by electrocatalytic reduction over palladium-loaded carbon felt

This brief review outlines work on effective hydrodechlorination of environmentally persistent chlorine-containing aromatic pollutants by electrocatalytic reduction at Pd-loaded carbon felt. The selective removal of chlorine from phenoxy herbicides 2,4-D and 2,4,5-T, chlorinated biphenyls and naphthalene was readily achieved (i) at room temperature and (ii) directly in aqueous media. No highly active reducing chemicals were required for such a treatment. The use of carbon felt of high surface area as a solution-permeable cathode offered high adsorption capacity for chloroaromatics, while supported palladium provided the system with a highly reactive reducing species supposed to be a surface-bound hydride, which was generated upon electrochemical reductive decomposition of water. A facilitating effect of bulky tetraalky lammonium cations of a supporting electrolyte on substrate conversion and product recovery is considered. The reaction mechanism for selective hydrodechlorination of chloroaromatics in aqueous media and scheme for activation of Pd-loaded carbon felt by electrolytic pre-treatment are proposed and discussed.