Catalytic hydrodechlorination of chlorinated olefins over a Pd/Al2O3 catalyst:: Kinetics and inhibition phenomena

The gas-phase hydrodechlorination of tetrachloroethene (TTCE), trichloroethene (TCE), and 1,1-dichloroethene (DCE) dissolved in toluene over a commercial Pd/Al2O3 (0.15% Pd) catalyst has been studied in a fixed-bed reactor working at space times in the range of 0-5 min(.)g/mmol of organochlorinated compound. The study includes both the influence of the temperature (in the range of 175-300 degreesC) on the kinetics of the hydrodechlorination of the single compounds and the kinetics for mixtures of these compounds at 250 degreesC. The observed order in reactivity is DCE > TCE > TTCE. The influence of the temperature on the kinetics can be satisfactorily modeled by a pseudo-first-order model and by considering an Arrhenius dependence for the kinetic constant. Important inhibition phenomena have been found by working with mixtures of organochlorinated compounds. These phenomena can be modeled considering a Langmuir-Hinshelwood model in which hydrogen (dissociatively chemisorbed) and all of the organochlorinated compounds are adsorbed in the same active sites.