Alumina-supported CuCl2, the basic catalyst for ethylene oxychlorination, has been investigated 1 hour after preparation by UV-vis spectroscopy, a solubility test, EPR, EXAFS, and XRD in a wide range (0.25-9.0 wt%) of Cu concentration. We have evidenced that, at low Cu content, the formation of a surface aluminate species takes place, where isolated Cu(II) ions occupy octahedral vacancies of the alumina surface, having (within experimental errors) five oxygen ligands at 1.92 +/-0.02 A. The chlorine released by copper chloride during its interaction with alumina gives >Al-Cl species. The formation of this surface copper aluminate stops at 0.95 wt% Cu/100 m(2); at higher Cu concentrations excess copper chloride precipitates directly from solution during the drying step, forming an amorphous CuCl2. 2H(2)O phase, overlapping progressively the surface aluminate. A slow hydrolysis, giving traces of paratacamite, an insoluble Cu hydroxochloride, also occurs. A room temperature dehydration process up to 10(-3) Torr implies the evolution of CuCl2. 2H(2)O into anhydrous CuCl2 as a consequence of the loss of the crystallization water. (C) 2000 Academic Press.