PROMOTER EFFECT OF ALUMINUM OXIDE ON ENHANCED HYDRODECHLORINATION OF CARBON TETRACHLORIDE WITH ZERO- VALENT ALUMINUM

摘要

The transformation of carbon tetrachloride by zero-valent aluminum (Al~0) under various pH conditions has been examined in the presence and absence of Al_2O_3. In the absence of Al_2O_3, carbon tetrachloride was primarily transferred to chloroform (68%) and dichloromethane (16%) at pH 3.0 while little of hydrodechlorination intermediates (7%) was found at pH 10. This indicates that carbon tetrachloride undergoes hydrodechlorination at low pH but not at high pH. The low production of hydrochlorination products could be attributed to the base-catalyzed hydrolysis of carbon tetrachloride resulting in the formation of carbon monoxide at high pH. It can not be detected by the provided analytic methods. In the presence of Al_2O_3, reaction rates increased as increasing the Al_2O_3 loading. Under alkaline conditions, the increase of selectivity towards the hydrodechlorination products was observed as the loading of Al_2O_3 increased. Reactions shifting from the possible base-catalyzed hydrolysis to hydrodechlorination suggested that Al_2O_3 serves as a proton donor in the degradation of carbon tetrachloride. Al_2O_3 is the key component of aluminosilicate, which is a composition of aquifer materials that have been found to increase the effectiveness of zero-valent iron. The present results provide a better understanding of the role of aluminosilicate minerals.