An FT-IR and Reactor Study of the Dehydrochlorination Activity of CuCl2/γ-Al2O3-Based Oxychlorination Catalysts

Abstract The conversion of ethylchloride into ethylene+HCl on pure and doped alumina supports and on CuCl 2 –Al 2 O 3 -based oxychlorination catalysts has been investigated by pulse reactor and FT-IR spectroscopy. FT-IR spectra of ethylchloride adsorbed on γ-Al 2 O 3 show weakly molecularly adsorbed species and ethoxy groups formed by nucleophilic substitution. Additionally, adsorbed diethylether is also observed. The analysis of the gas-phase species shows that ethoxy groups decompose, giving rise to ethylene at 523 K. Under the same conditions, gaseous HCl is also released from the surface and diethylether is also observed in the gas phase. Chlorination of alumina with HCl only partially hinders the dehydrochlorination mechanism occurring through ethoxy groups. Experiments performed on alumina doped with MgCl 2 and KCl indicate that the site reactivity scale for EtCl conversion to ethylene is the following: bare Al 2 O 3 >CuCl 2 on Al 2 O 3 >MgCl 2 on Al 2 O 3 >KCl on Al 2 O 3 . Doping with MgCl 2 and in particular with KCl limits the activity of the bare support in the dehydrochlorination. These data strongly support the previous proposal that the exposed alumina surface catalyzes the dehydrochlorination of EDC to VCM, with a consequent loss in selectivity in the oxychlorination reactor. The beneficial effect of doping with KCl and MgCl 2 is due to the reduced dehydrochlorination activity.