A complete catalytic cycle was performed on CuCl2/Al2O3 catalyst for ethylene oxychlorination at 500 K. X-ray absorption near-edge spectroscopy, extended X-ray absorption fine structure, electron paramagnetic resonance, and IR of adsorbed CO were used to demonstrate that the ethylene oxychlorination reaction, C2H4 + 2HCl + 1/2O(2) --> C2H4Cl2 + H2O, follows a three-step mechanism: (i) reduction of CuCl2 to CuCl (2CuCl(2) + C2H4 --> C2H4Cl2 + 2CuCl), (ii) oxidation of CuCl to give an oxychloride (2CuCl + 1/2O(2) --> Cu2OCl2), and (iii) closure of the catalytic circle by rechlorination with HCl, restoring the original CuCl2 (Cu2OCl2 + 2HCl --> 2CuCl(2) + H2O). The dispersing/sintering effect of the different reagents on the active phase has been also investigated.