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

Abstract 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/Al 2 O 3  + soluble Fe 2+ ) and fully heterogeneous (FePd/Al 2 O 3 ) catalytic systems under ambient conditions. In contrast to bulk H 2 O 2 production conditions, hydrazine is able to produce H 2 O 2 in situ followed by phenol degradation using Pd/Al 2 O 3  + Fe 2+ 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 H 2 O 2 at the inherent acidic pH of hydroxylammonium sulfate in the presence of Pd/Al 2 O 3  + Fe 2+ was also found to differ from the bulk production of H 2 O 2 , in which no H 2 O 2 was detected. A remarkable degree of mineralization (ca. 65%) as well as fast phenol degradation during the reaction started at pH 7 over FePd/Al 2 O 3 may be an advantage of using hydroxylamine. On the other hand, using formic acid, H 2 O 2 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.