Palladium-silver sol-gel catalysts for selective hydrodechlorination of 1,2-dichloroethane into ethylene III. Kinetics and reaction mechanism

The kinetics of selective hydrodechlorination of 1,2-dichloro-ethane into e thylene over a Pd-Ag/SiO2 catalyst is studied. Kinetic data at 573, 596, an d 647 K have been obtained by means of experimental designs in the space of the partial pressures of the four components influencing kinetics, that is , 1,2-dichloroethane, hydrogen, ethylene, and hydrogen chloride. One model among the numerous ones examined allows us to represent correctly the exper imental data. Ii: corresponds to the following mechanism: dechlorination of 1,2-dichloroethane into ethylene occurs on silver through dissociative ads orption with successive breaking of the two C-Cl bonds and desorption of C2 H4. Thanks to its activation power of hydrogen by dissociative chemisorptio n, palladium present at the surface of the alloy supplies hydrogen atoms fo r regeneration of the chlorinated silver surface into metallic silver. The presence of hydrogen adsorbed on Pd also causes the undesired ethylene hydr ogenation leading to a loss of olefin selectivity. (C) 2001 Academic Press.