Alumina-supported copper chloride 2. Effect of aging and thermal treatments

The effect of aging and heating treatments up to 500 K on alumina-supported CuCl2, i.e., the base catalyst for ethylene oxychlorination, has been inve stigated by UV-vis spectroscopy, a solubility test, EXAFS, XRD, and EPR in a wide range (0.25-9 wt%) of Cu concentration. It is shown that the catalys t undergoes significant changes with both time and thermal treatments, so a ccounting for some contradictory results reported in the literature. While the surface Cu aluminate (formed during impregnation) does not change upon aging and heating, supported CuCl2 (precipitated from impregnating solution during the drying process) undergoes a slow hydrolysis reaction with the f ormation of paratacamite and HCl, The HCl formed during the hydrolysis reac ts with the alumina surface with the formation of >Al-Cl species. Upon heat ing, the initially formed paratacamite can react with surface >Al-Cl specie s with nearly total restoration of CuCl2, which is consequently the main sp ecies present on the catalyst at the beginning of the oxychlorination react ion. The obtained picture is able to explain the results emerging from acti vity tests on the whole set of catalysts, indicating that surface aluminate is not active and that the active phase is CuCl2. (C) 2000 Academic Press.