Generation of hydrogen peroxide via the selective reduction of oxygen by hydrazine sulfate over Br-promoted Pd/Al<SUB>2</SUB>O<SUB>3</SUB> catalyst in an aqueous medium at ambient conditions

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