A layered FeII-FeIII hydroxide (green rust, GR) was intercalated with dodecanoate (known as GRC12) and then amended with CuII (GRC12(Cu)) before reaction with chloroform (CF), carbon tetrachloride (CT), trichloroethylene (TCE) or tetrachloroethylene (PCE). Reduction of CT by GRC12(Cu) was 37 times faster than with GRC12 alone before the active Cu species was consumed. The Cu mediated reaction followed the dichloroelimination pathway as observed for GRC12 alone, with carbon monoxide (82.5%) and formate (26.6%) as main degradation products. Also, CF was reduced by GRC12(Cu), which is not seen with GRC12. Neither GRC12(Cu) nor GRC12 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 GRC12 was reduced to CuI by FeII in GR, but CuI 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 CuI 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.