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 150°C on, void residence times ∼1.5s, with various H2:N2 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 150°C, giving HCl, benzene and cyclohexane. Ten weight percent Ni on Norit ROW 0.8 Supra was an active catalyst too, with T50%∼190°C, which reaction is ∼5 orders of magnitude faster than on this AC alone. Products are HCl and benzene. Ten weight percent Ni on γ-Al2O3 has a lower hydrodechlorination (HDCl) activity for PhCl, with T50%∼250°C. For CH the γ-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 300°C 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, 10wt.% Ni on AC (Rhein Braun lignite fine, or Norit ROW) were the better catalysts, with rates ∼10 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 10wt.% 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, 10wt.% Ni on Norit ROW 0.8 Supra appeared to be the best catalyst. Mechanisms are briefly discussed.