Dechlorination of chlorinated ethenes and acetylenes by palladized iron

The degradation of chlorinated ethenes and acetylenes by palladium coated iron was studied in batch experiments. The reactivity of palladium coated iron with tetrachloroethene and its less chlorinated ethene and acetylene derivatives showed that dechlorination rates increased as the number of chlorines decreased. Thus, vinyl chloride, the most toxic compound in the chlorinated ethenes, was most rapidly degraded by the palladium coated iron. This reactivity order is opposite to the results previously observed with plain zero valent metals. The major dechlorination products of trichloroethene were ethane, ethene, and acetylene and the carbon mass balance was found to be about 81-91%. No chlorinated products were detected indicating that multiple or concerted dechlorinations rather than sequential reactions were occurring on palladium coated iron. The proposed reaction pathway is that once the chlorinated ethenes have adsorbed on the metal surface, all the chlorines are removed before desorption without release of less chlorinated products such as dichloroethenes and vinyl chloride. As the palladium content increased from 0.025% to 0.77%, the reaction rate was increased. The reaction rate increased linearly up to 0.098% of palladium, however, the increasing rate diminished with higher amounts of Pd. Results of Energy Dispersive X-ray Spectroscopy showed that uneven palladium coatings were formed on the iron at high contents of palladium.