Kinetics of the hydrodechlorination reaction of chlorinated compounds on palladium catalysts.

摘要

Hydrodechlorination is the reaction of a chlorinated organic compound (R-Cl) with hydrogen to form a carbon-hydrogen bond and HCl: R-Cl + H 2 = R-H + HCl. In this research work, we studied four families of chlorinated compounds; CF3CF3−xClx(x = 1–3), CH4−xClx (x = 1–4), CF4−xCl x (x = 1–4) and dichloropropanes (1,1-, 1,2-, 1,3-, 2,2-), on supported palladium catalysts to create a theory capable of predicting the hydrodechlorination rate on chlorinated compounds and to explore the reaction mechanism.;The proposed reaction steps were examined by both isotope-exchange experiments and reaction energetics measurement. The hydrodechlorination reaction of CF 3CFCl2 was performed in the presence of H37Cl to study the reversibility of C-Cl bond scission, and the removal of the first Cl atom from CF3CFCl2 was found to be an irreversible step. Hydrodechlorination experiments of CF3CFCl 2 with D2 and HCl mixture revealed that D2 and HCl were in equilibrium with surface adsorbed hydrogen and chlorine during reaction. The forward rate and reverse rate of this equilibrium were at least 400 times higher than the overall hydrodechlorination rate. This result supported the assumption of equilibrium for 2HCl + 2* ↔ H2 + 2Cl*. Additionally, the activation energy for the rate determining step was extracted from hydrodechlorination reaction kinetics results of CH4−xClx (x = 1–4), CF4−xClx (x = 1–4) and dichloropropanes (1,1-, 1,2-, 1,3-, 2,2-) compounds. It was found that for each of the series compounds, a linear relationship existed between C-Cl bond scission activation energy and gas phase C-Cl bond strength. This observation corroborates our assumption that the removal of the first Cl atom from a chlorinated compound is the rate-determining step in the hydrodechlorination reaction. Thus, all kinetic and isotope experimental results obtained from this study are consistent with the proposed reaction steps for the chlorinated compounds tested.;Some work has been done to study hydrodechlorination reaction steps and reaction intermediates beyond the rate-limiting step. (Abstract shortened by UMI.).