A layered Fe-II-Fe-III hydroxide (green rust, GR) was intercalated with dodecanoate (known as GR(C12)) and then amended with Cu-II (GR(C12)(Cu)) before reaction with chloroform (CF), carbon tetrachloride (CT), trichloroethylene (TCE) or tetrachloroethylene (PCE). Reduction of CT by GR(C12)(Cu) was 37 times faster than with GR(C12) alone before the active Cu species was consumed. The Cu mediated reaction followed the dichloroelimination pathway as observed for GR(C12) alone, with carbon monoxide (82.5%) and formate (26.6%) as main degradation products. Also, CF was reduced by GR(C12)(Cu),which is not seen with GR(C12). Neither GR(C12)(Cu) nor GR(C12) reacted with PCE or TCE. The chlorinated solvents can partition into dodecanoate interlayer but only small CS molecules (CF, CT) can transport through the dodecanoate interlayer. Copper(II) added to GR(C12) was reduced to Cu-I by Fe-II in GR, but Cu-I was not regenerated during the dechlorination. High resolution TEM showed that Cu was evenly distributed in the GR without formation of Cu nanoparticles on edges of GR. The active Cu-I sites are most likely located between the iron hydroxide layer and the hydrated negatively charged carboxylate groups in the interlayer of GR. This work shines new light on the Cu accelerated dechlorination by GR. (C) 2017 Elsevier B.V. All rights reserved.