Hydrodechlorination of CCl4 over group VI transition metal carbides

Hydrodechlorination of carbon tetrachloride (CCl4) was investigated on group VI metal carbides (WC, W2C, Mo2C) prepared by temperature programmed carburization of WO3 and MoO3 in 10–20% CH4/H2 mixtures. Their catalytic performances have been compared with those of 1 wt.% Pt/γ-Al2O3 catalyst. Experiments were carried out at atmospheric pressure in a fixed bed flow reactor at 120 and 250 °C with a molar ratio H2/CCl4=12. WC shows the best selectivity towards chloroform (CHCl3), whatever the temperature and particularly at 120 °C (selectivity above 99%) while W2C and Mo2C produce tetrachloroethylene in substantial amount. Mo2C and W2C deactivate rapidly with time irrespective of the temperature, whereas WC exhibits a good stability at 120 °C. Surface characterization indicates that the deactivation on M2C (M=Mo, W) could be correlated to the formation of a chlorocarbonaceous polymer.