Hydrodechlorination reactions on silica-supported rhodium catalysts

The objectives of this study were to investigate the pathways of the hydrodechlorination reactions over silica-supported Rh catalysts as well as identify selectivities and deactivation properties. Reaction of 1,2-dichloroethane with hydrogen over Rh/SiO2 catalyst was studied in the temperature range 200 to 300°C. Formation of two intermediates was proposed while 1,2-dichloroethane was adsorbed on the catalyst, the reactive intermediates then produce ethane, ethylene, chloroethane and methane. From the methane formation, it was inferred that the ethane hydrogenolysis occured over the Rh/SiO2 catalysts. Higher conversion to C1 and C2 hydrocarbons was observed at higher reaction temperature. The activation energy was found to be 13 Kcal/mole. Hydrodechlorination of trichloroethylene was studied to gain information on controlling parameters to manage trichloroethylene pollution emissions in vapor-degreasing applications. Reaction temperature above 150°C, longer contact time, and reactant partial pressure below 100 torr effectively promoted the conversion to hydrocarbon formation. The activation energy was 13.9 Kcal/mole. The data showed that two Cl atoms on the α( carbon did not need to be removed simultaneously during the reaction. The deactivation on Rh/SiO2 catalyst was also studied. A comparion of the ethylene hydrogenation on fresh and contaminated catalysts (after reaction with 1,1-dichloro-ethane) showed a negative effect on the product selectivity to ethane formation, for the deactivated catalyst. The varied selectivity for CH4 and C2H6 demonstrated that at least two distinct types of active sites existed on the catalyst surface