Electrocatalytic properties of transition metals toward reductive dechlorination of polychloroethanes

Chlorinated volatile organic compounds (VOCs) such as polychloromethanes and polychloroethanes (PCEs) are among the most ubiquitous pollutants in the environment. Reductive electrochemical dechlorination at catalytic cathodes is one of most promising methods of abatement of these pollutants. In this study, the electrochemical reduction of several PCEs has been investigated in DMF + 0.1 M (C3H7)4NBF4 at Ag, Au, Pd, Pt, Cu, Fe, Ni, Pb, Zn and glassy carbon (GC), the last used as a reference system with negligible catalytic properties. The reduction potentials of all investigated PCEs are remarkably influenced by the nature of the electrode material and the chemical structure of the compound. In any case, Ag, Cu, and Au show powerful electrocatalytic activities. Based on voltammetric investigations on all PCEs and electrolyses of 1,1,1-trichloroethane and 1,1,1,2-tetrachloroethane in different conditions, the reduction mechanism is shown to be strongly dependent on the nature of the PCE. Geminal PCEs undergo a sequential hydrodechlorination mechanism in which one chlorine atom is lost in each reduction step until a completely dechlorinated ethane is obtained. In contrast, reduction of vicinal PCEs involves removal of two chlorine atoms in an overall 2e− process resulting in the formation of the corresponding (chloro)ethylene, which may be further reduced at more negative potentials.