Catalytic hydrodechlorination of groundwater contaminants in water and in the gas phase using Pd/γ-Al2O3

Pd/γ-Al2O3 can be used as a hydrodechlorination catalyst for both the water and the gas phase. A comparison of the catalytic hydrodechlorination of 1,1,2,2-tetrachloroethane (TeCA) in water and in the gas phase at various temperatures with Pd/γ-Al2O3 revealed Arrhenius parameters identical for the reaction in both phases: ln (APd (l/(g min))) = 22.8±0.9, EA=58.0±2.3 kJ/mol. Catalysts are deactivated by sulphur compounds but can be fully regenerated by oxidative treatment at elevated temperatures. A selectivity shift depending on the catalyst deactivation state was observed: unsaturated chlorocompounds react with the highest rate on fresh catalyst, whereas on partially deactivated catalysts saturated compounds such as tetrachloroethane are most rapidly dechlorinated. Apparently, saturated and unsaturated chloroorganic compounds react via different mechanisms. The relative reactivities of the CCl and CBr bonds in bromochloromethane (BCM) are temperature dependent. At a low temperature (100 °C) methyl chloride is the dominant side product, whereas at a higher temperature (200 °C) methyl bromide is preferred.