Hydrodechlorination of 1,2-dichloroethane on active carbon supported palladium–nickel catalysts

Two series of 2 wt.% Pd–Ni/active carbon catalysts prepared from chloride and nitrate salts were characterized by hydrogen chemisorption, temperature programmed palladium hydride decomposition and X-ray diffraction, and investigated in the hydrodechlorination of 1,2-dichloroethane in the gas phase at a relatively low reaction temperature (210–230 °C). All catalysts showed very high stability with time on stream. Ni-rich bimetallic samples exhibited the highest selectivities towards ethene (desired reaction product). Addition of palladium, the metal which is known for its high hydrogenation activity, resulted in a massive production of ethane, at the expense of ethene. The correlation between the turnover frequency towards ethene and Pd–Ni phase composition resembles very much an expected relationship between surface and bulk composition of Pd–Ni alloys. This suggests that surface nickel atoms are the active sites for hydrogen-assisted dechlorination of 1,2-dichloroethane. The overall results indicate that, in agreement with the literature, palladium segregates to the surface of Pd–Ni (even during hydrodechlorination), shaping the overall catalytic behavior of bimetallic Pd–Ni catalysts. The monometallic, 2 wt.% Ni/C prepared from the chloride precursor, was the only catalyst which showed a noticeable selectivity for vinyl chloride which gradually increased with time on stream. The temperature programmed hydrogenation of deposits left after the reaction showed the presence of surface carbon and rather negligible amounts of chlorine.