Transformation of chlorinated methanes by zero-valent aluminum coupled with Pd/Al2O3.

The transformation of chlorinated methanes by zero-valent aluminum under various pH conditions has been examined in the presence and absence of Pd/Al2O3. In the absence of Pd/Al2O3, carbon tetrachloride was primarily transferred to chloroform (65%) and dichloromethane (15.3%) at pH 2.5 while little of the hydrodehalogenation intermediates (approximately 5%) was found at pH 10.8. This indicates that carbon tetrachloride undergoes hydrodehalogenation at low pH but not at high pH. The low production of hydrodehalogenation intermediates at high pH could be attributed to the base-catalyzed hydrolysis of carbon tetrachloride resulting in the formation of products that can not be detected by the provided analytic methods. In the presence of Pd/Al2O3, degradation rates were increased by a factor of 10-43 compared to the system without Pd/Al2O3, suggesting Pd/Al2O3, serves as a catalyst. Further, complete degradation of carbon tetrachloride by zero-valent aluminum with Pd/Al2O3 led directly to methane (86.4%) without formation and accumulation of dichloromethane at pH 9.0. The direct transformation of carbon tetrachloride to methane can be rationalized by the catalytic hydrodehalogenation occurring at the palladium surface. The study indicates aluminum coupled with Pd/Al2O3 is an environmentally-friendly technology for treatment of chlorinated organic contaminants.