Influence of transition metal additives and temperature on the rate of organohalide reduction by granular iron: Implications for reaction mechanisms

This study provides mechanistic insights into the reduction of organohalides by granular iron as well as the origin of the rate enhancements typically observed when transition metals are added to the surface of granular iron. Using step-wise displacement plating of CuCl2, K2PdCl4 and K2PtCl4, different bimetallic and trimetallic reductants were prepared and characterized using a suite of analytical techniques that included energy filtered transmission electron microscopy (EFTEM). Results obtained from batch studies with the trimetals indicate that reactivity enhancements of 1,1,1-trichloroethane (1,1,1-TCA) reduction are controlled by the chemical identity of the transition metal additive at the liquid/solid interface. Temperature-dependent studies involving iron and bimetals revealed that rates of 1,1,1-TCA reduction increased exponentially with increasing temperature. A systematic shift in product distribution towards more fully hydrogenated products was also observed as the overall rate of 1,1,1-TCA reduction increased. Collectively, these results support recent studies, which suggest that atomic hydrogen is involved in the reduction of alkyl polyhalides by granular iron and bimetallic reductants.