Doped CuCl2/Al2O3 is an industrial catalyst used to produce dichloroethane, key intermediate of the polyvinyl chloride (PVC) chemistry. Using in situ and operando X-ray absorption spectroscopies, combined with laboratory techniques, we succeeded in understanding the nature of the active phase and the role played by most used additives for fluid and fixed beds technologies (LiCl, KCl, CsCl, MgCl2, and LaCl3). Moreover we were able to quantify relative fraction, reducibility and dispersion of Cu-phases adjoining catalytic tests in a pulse reactor. EXAFS and XANES highlighted that all additives contribute more or less efficiently in increasing the fraction of the active species (supported CuCl2). EXAFS directly, UV–vis and IR spectroscopies indirectly proved the formation of mixed salts, when KCl or CsCl are added, so displacing the rate determining step from the CuCl oxidation to the CuCl2 reduction. Fully oxidized catalyst is inactive, so copper in the working catalyst, exhibits a I/II mixed valence state. Coupling the ethylene conversion, measured with a pulse reactor, with XANES spectra collected after interaction with C2H4, we could differentiate the ability of doped samples to be reduced by ethylene. We obtained slightly different results explainable by the different dispersion of the active phase, measured by CO chemisorption.