In a study on oxychlorination of ethylene using KCl-promoted CuCl2/Al2O3 catalyst having a composition similar to that of a commercial catalyst, steady-state catalyst composition was determined over a wide range of temperature after identifying the surface copper species by X-ray photoelectron spectroscopy (XPS). The data show a marked shift in the steady-state catalyst composition at about the same temperature at which structural change had been previously reported for similar catalysts. This is confirmed in a separate study of the CuCl2-ethylene reaction which is considered to be the key intermediate step in the overall oxychlorination reaction network.