Generation of hydrogen peroxide via the selective reduction of oxygen by hydrazine sulfate over Br-promoted Pd/Al₂O₃ catalyst in an aqueous medium at ambient conditions

Abstract

The in situ generation of H₂O₂ via the selective reduction of O₂ by hydrazine sulfate (in an aqueous medium) has been thoroughly investigated over the Br-promoted Pd(or PdO)/Al₂O₃ catalyst. The influence of the following factors have been addressed in this study: (a) Br concentration (in the reaction medium or incorporated in the catalyst); (b) reaction conditions (viz. reaction time, temperature); (c) concentrations of reducing agent and phosphoric acid in the reaction medium. Decomposition of N₂H₄ (from N₂H₄.H₂SO₄) and its reaction with H₂O₂ under similar reaction conditions (in the absence of O₂) have also been studied. H₂O₂, which is an intermediate product of the O₂ reduction, is involved in further consecutive reactions. It can be converted to water via its decomposition and/or reaction with the unconverted N₂H₄. In the presence of Br promoter, the later (reaction with unconverted N₂H₄) is more dominant. Both the consecutive reactions are drastically retarded in the presence of protons and Br promoter. A plausible reaction mechanism has been proposed for illustrating the role of the protons and Br promoter in the selective formation of H₂O₂ in the O₂ reduction process.