Iron powder, graphite and activated carbon as catalysts for the oxidation of 4-chlorophenol with hydrogen peroxide in aqueous solution

Solid materials as iron powder, graphite and activated carbon were tested for their catalytic properties for the oxidation of 4-chlorophenol in aqueous solution with hydrogen peroxide. Batch tests were performed at 30 degrees C, and continuous tests with granular activated carbon under ambient conditions (20 degrees C). Iron powder was shown to act as a catalyst for the activation of hydrogen peroxide and owing to this for the oxidation of 4-chlorophenol. The catalytic activity is based on iron ions leached from the iron powder which act as homogeneous catalysts. Thus, the process can be described as a Fenton reaction enabled by a dissolution of iron powder. The same phenomenon was observed when iron impregnated activated carbon was applied as a catalyst. In contrast to iron powder, graphite and activated carbon were found to act as heterogeneous catalysts for the activation of hydrogen peroxide and the oxidation of 4-chlorophenol: During the oxidation of 4-chlorophenol with activated carbon as a catalyst the decomposition of H2O2 is significantly slower than in the absence of 4-chlorophenol. This can be explained by the adsorption of 4-chlorophenol, due to which the surface area of the activated carbon available for the decomposition of H2O2, is reduced. At the same concentration of catalytic material in batch tests, the oxidation 4-chlorophenol proceeds much faster when iron powder instead of graphite or activated carbon is used. On the other hand, graphite and activated carbon are stable catalysts not affected by dissolution processes. Activated carbon can be utilized for a continuous process in a fixed bed reactor. For this purpose the efficiency of 4-chlorophenol oxidation in granular activated carbon filled columns was investigated and a 25% conversion of the 4-chlorophenol (1 g l(-1)) was achieved at a retention time of 26 min. (C) 1998 Elsevier Science Ltd. Ail rights reserved.