Hydrodechlorination of CCl_4 over group VI transition metal carbides

摘要

Hydrodechlorination of carbon tetrachloride (CCl_4) was investigated on group VI metal carbides (WC, W_2C, Mo_2C) prepared by temperature programmed carburization of WO_3 and MoO_3 in 10-20% CH_4/H_2 mixtures. Their catalytic performances have been compared with those of 1 wt.%a Pt/#gamma3-Al_2O_3 catalyst. Experiments were carried out at atmospheric pressure in a fixed bed flow reactor at 120 and 250 deg C with a molar ratio H_2/CCl_4 = 12. WC shows the best selectivity towards chloroform (CHCl_3), whatever the temperature and particularly at 120 deg C (selectivity above 99%) while W_2C and Mo_2C produce tetrachloroethylene in substantial amount. Mo_2C and W_2C deactivate rapidly with time irrespective of the temperature, whereas WC exhibits a good stability at 120 deg C. Surface characterization indicates that the deactivation on M_2C (M = Mo, W) could be correlated to the formation of a chlorocarbonaceous polymer.