Hydrodechlorination of chloromethanes with Pd on activated carbon catalysts for the treatment of residual gas streams

Abstract

Laboratory-prepared Pd/C catalysts have been investigated in the deep gas-phase hydrodechlorination (HDC) of monochloromethane (CH3Cl), dichloromethane (CH2Cl2) and trichloromethane (CHCl3). The catalysts were found to be active in HDC, the reactivity following the order CHCl3 > CH2Cl2 > CH3Cl. Selectivities to non-chlorinated compounds were found to be higher than 90% in most cases. The results obtained with the catalyst prepared from PdCl2 suggest that all the reaction products are primary products. The CH4, CH3Cl and CH2Cl2 come from the hydrogenation of the corresponding adsorbed chloride radical, while hydrocarbons of more than one carbon atoms are formed by reaction and subsequent hydrodechlorination of two radicals adsorbed in neighbouring active centers. The catalyst undergoes a significant deactivation which appears to be due to the poisoning of active centers with chlorinated hydrocarbons. The use of Pd(NO3)2 as Pd precursor leads to a decrease in the activity due to its lower Pd dispersion and a lower proportion of electrodeficient Pd species.