[Dechlorination mechanisms of chlorinated hydrocarbons by supported nanoscale Pd/Fe]

Some volatile chlorinated hydrocarbons such as VC, 1,1-DCE, TCE, PCE, gamma-HCH, were dechlorinated by synthesized supported nanoscale Pd/Fe. The dechlorination reactions of PCE, TCE, 1,1-DCE, VC, gamma-HCH follow the pseudo-frist order kinetics equations with the k(obs) of 2.79 h(-1), 2.35 h(-1), 1.12 h(-1), 2.14 h(-1) and 4.02 h(-1) respectively. Little or no medial products were detected and the main end products were C2H6 and C2H4 during the dechlorination of VC, 1,1-DCE, TCE, PCE. The total carbon ratio of C2H6 and C2H4 were 70% and 10% respectively during the dechlorination of TCE. The supported nanoscale Pd/Fe particles after exposed to air for 24 h were used for 8 cycle experiments and the results indicate that the particles have favorable stability. The reactivity has no obvious decrease after 200 hours' successive dechlorination experiments of gamma-HCH which indicates that the particles represent good durability. The reaction activation energy of all the chlorinated hydrocarbons are bigger than 29 kJ x mol(-1) which shows that the surface-chemical reaction rather than diffusion is the rate-limiting step in the metal-mediated dechlorination process. A consistence between the experimental data and simulated curves indicates that the muti-step reaction pathways proposed offer a better explanation of the reaction mechanisms than sequential hydrogenolysis reactions in the transformation of chlorinated hydrocarbons by supported nanoscale Pd/Fe.