Complete hydrodechlorination of chlorobenzene and its derivatives over supported nickel catalysts under liquid phase conditions

Liquid phase hydrodechlorination of chlorobenzene was studied over Ni/active carbon (Ni/AC), Ni/gamma-Al2O3, Ni/SiO2 and Raney Ni. The complete hydrodechlorination of chlorobenzene was realized at 333-343 K on Ni/AC under hydrogen atmosphere of 1.0 MPa in the presence of alkaline hydroxide. Aryl halides, three chlorotoluenes (o-, m- and p-), three chloroanilines, three chlorobenzotrifluorides, three dichlorobenzenes and two trichlorobenzenes (1,2,3- and 1,2,4-) were also completely hydrodechlorinated under the similar conditions. Chlorobenzene derivatives having either an electron-donating group or an electron-withdrawing group decreased their reactivities with respect to the unsubstituted chlorobenzene. The reactivities of polychlorinated benzenes slightly decreased with the increasing chlorine atom number in a molecule. The steric effect of trichlorobenzene gave a large influence on the product distribution. The reaction rate did not depend on chlorobenzene concentration and increased with increasing hydrogen pressure. The reaction did not proceed in the absence of alkaline hydroxide. The active catalysts were characterized by hydrogen chemisorption and transmission electron microscopy techniques. The apparent activity strongly depends on the active surface area of nickel on catalyst surface. Based on the above results, the reaction route was discussed. The deactivation of Ni catalyst was observed in the dechlorinating process. An accumulation of CaCl on the catalyst surface is probably one of the reasons for the deactivation. The deactivated catalysts can be partially recovered by washing with distillated water and reactivating. (c) 2005 Elsevier B.V. All rights reserved.