Hydrogen substitutes for the in situ generation of H2O2: An application in the Fenton reaction

This study investigates the ability of formic acid, hydrazine and hydroxylamine to act as H-2 substitutes in conducting phenol degradation by Fenton reaction using in situ generated hydrogen peroxide. The processes were performed with semi-heterogeneous (Pd/Al2O3 + soluble Fe2+) and fully heterogeneous (FePd/Al2O3) catalytic systems under ambient conditions. In contrast to bulk H2O2 production conditions, hydrazine is able to produce H2O2 in situ followed by phenol degradation using Pd/Al2O3 + Fe2+ at pH 3 without the need for halide ions. However, a degree of mineralization exceeding 37% could not be achieved. The significant production of in situ H2O2 at the inherent acidic pH of hydroxylammonium sulfate in the presence of Pd/Al2O3 + Fe2+ was also found to differ from the bulk production of H2O2, in which no H2O2 was detected. A remarkable degree of mineralization (ca. 65%) as well as fast phenol degradation during the reaction started at pH 7 over FePd/Al2O3 may be an advantage of using hydroxylamine. On the other hand, using formic acid, H2O2 was produced at a moderate rate, thereby achieving higher efficiency in the mineralization of phenol. Most importantly, the catalysts were more stable in the presence of formic acid than hydrazine or hydroxylamine. (C) 2011 Elsevier B.V. All rights reserved.