Performance of supported nickel and other metal catalysts in the hydrodechlorination of chlorobenzene and 1-chlorohexane

Vapours of chlorobenzene (PhCl) and 1-chlorohexane (CH) diluted with octane have been (hydro)dechlorinated using Ni, Fe, W, Ni-Mo, Pt and Pd on activated carbon (AC) or on Al2O3, at temperatures from 150degreesC on, void residence times similar to1.5 s, with various H-2:N-2 ratios, usually 1:3, as a carrier gas. For PhCl, Pd on AC was found to be the most active catalyst, with nearly complete reaction even at 150degreesC, giving HCl, benzene and cyclohexane. Ten weight percent Ni on Norit ROW 0.8 Supra was an active catalyst too, with T-50% similar to 190degreesC, which reaction is similar to5 orders of magnitude faster than on this AC alone. Products are HCl and benzene. Ten weight percent Ni on gamma-Al2O3 has a lower hydrodechlorination (HDCl) activity for PhCl, with T-50% similar to 250degreesC. For CH the gamma-Al2O3 supported catalysts have high rates; the reaction apparently takes place on the support. The products, hexane and hexenes, are cracked into lighter products above 300degreesC accompanied by coke formation on the surface of the alumina. Carbon supported catalysts have a lower activity but under the applied conditions deactivation was negligible. For CH, 10 wt.% Ni on AC (Rhein Braun lignite fine, or Norit ROW) were the better catalysts, with rates similar to10 times higher than for the support alone and some 12 orders of magnitude higher than for the gas-phase reaction. Also the influence of the hydrocarbon diluent on rates has been exemplified for the 10 wt.% Ni/ROW catalyst by replacing n-octane by n-hexane or n-decane. If a waste stream has to be treated containing both aliphatic and aromatic chlorine, 10 wt.% Ni on Norit ROW 0.8 Supra appeared to be the best catalyst. Mechanisms are briefly discussed. (C) 2004 Elsevier B.V. All rights reserved.