Catalytic wet oxidation with H2O2 of carboxylic acids on homogeneous and heterogeneous Fenton-type catalysts

The catalytic wet oxidation with hydrogen peroxide (WHPO) of diluted formic, acetic and propionic acid solutions (total organic carbon of 30 mg C/l) in the 25-70 degrees C temperature range using a Fe3+-containing zeolite (Fe/ZSM5) is compared with the behavior of homogeneous Fe3+ catalysts at the same experimental conditions. Although the heterogeneous catalysts have a higher reactivity and a reduced dependence on the pH of the solution in comparison to the homogeneous Fe3+ catalysts, they also have a higher rate of the side reaction of hydrogen peroxide decomposition to water and oxygen. Leaching tests indicate that the activity of the heterogeneous catalyst is not due to leached iron ions, although a small amount of iron was found in the aqueous solution. It was also observed that catalytic behavior could be reproduced in consecutive catalytic experiments, but an intermediate calcination step is necessary to oxidize the organic species which remain trapped inside the pore of the zeolite. (C)2000 Elsevier Science B.V. All rights reserved.