Gas-phase hydrodechlorination of dichloromethane with activated carbon-supported metallic catalysts

The deep gas-phase hydrodechlorination (HDC) of dichloromethane (DCM) was studied over several laboratory-made activated carbon-supported metallic catalysts (Pd/C, Pt/C, Ru/C and Rh/C) at atmospheric pressure, reaction temperatures in the 200–250 °C range and space-times of 0.08 and 1.7 kg h mol−1. All the catalysts showed a high activity in HDC of DCM, with conversions in the range 89–99% at the highest temperature and space-time investigated, following the order Rh > Pd > Ru > Pt. Selectivities to non-chlorinated products up to 95% were reached. Methane was the main reaction product in all cases. Hydrodechlorination of DCM with Pt/C catalyst exclusively yielded methane and monochloromethane while hydrocarbons of more than one carbon atom were obtained with the other catalysts. The Pt/C catalyst was highly stable with no loss of activity after 65 h of time on stream at the testing conditions. The deactivation was more pronounced in the case of Ru (DCM conversion decreased a 40% after 20 h of operation), followed by Pd and in a less extent Rh with conversion decreases of 40 and 9%, respectively, after 65 h on stream. The fresh and used catalysts were characterized by N2 adsorption–desorption, ICP-MS, TPR, XRD, XPS and H2 and CO chemisorptions. Characterization results suggest that deactivation is mainly related to a decrease of the exposed metallic surface area along the reaction, which appears to be due to poisoning of active centers with chlorinated hydrocarbons, and in the case of Ru/C catalyst also metal sintering.