The CuCl2/Al2O3 Catalyst Investigated in Interaction with Reagents

Alumina supported CuCl2, the basic catalyst for ethylene oxychlorination, has been investigated by UV-Vis spectroscopy, EPR, EXAFS and XANES 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. The formation of this surface copper aluminate stops at 0.95 wt% Cu / 100 m; at higher Cu concentrations excess copper chloride precipitates directly from solution during the drying step forming an highly dispersed CuCl2 . H2O, phase, overlapping progressively the surface aluminate. Depletion tests and IR spectroscopy of adsorbed NO have demonstrated that the latter is the only active phase. A complete catalytic cycle has then been performed on CuCl2/Al2O3 catalyst. EPR, XANES and EXAFS, have been used to demonstrate that the ethylene oxychlorination reaction: C2H4 + 2HCl + 1⁄2 O2 → C2H4Cl2 + H2O follows a three steps mechanism: (i) reduction of CuCl2 to CuCl (2CuCl2 + C2H4 → C2H4Cl2 + 2CuCl), (ii) oxidation of CuCl to give an oxychloride (2CuCl + 1⁄2 O2 → Cu2OCl2) and (iii) closure of the catalytic circle by rechlorination with HCl, restoring the original CuCl2 (Cu2OCl2 + 2HCl → 2CuCl2 + H2O). Finally, we have shown that time resolved, in situ, spectroscopy is a very promising technique to investigate the interplay between catalyst activity and oxidation state of copper.