Direct H<SUB>2</SUB>-to-H<SUB>2</SUB>O<SUB>2</SUB> oxidation over highly active/selective Br-F-Pd/Al<SUB>2</SUB>O<SUB>3</SUB> catalyst in aqueous acidic medium: Influence of O<SUB>2</SUB>/H<SUB>2</SUB> ratio and other reaction conditions on the H<SUB>2</SUB>O<SUB>2</SUB> formation

The influence of the O<SUB>2</SUB>/H<SUB>2</SUB> mole ratio in the gaseous feed and also those of other reaction conditions [viz. concentration of H<SUB>3</SUB>PO<SUB>4</SUB> (0-5 mol/dm<SUP>3</SUP>), temperature (5-50 ° C), gas (H<SUB>2</SUB> and O<SUB>2</SUB>) space velocity (5.8-23.4 h-1) and reaction time (0.1-8 h)] on the H<SUB>2</SUB>O<SUB>2</SUB> formation in the H2-to-H<SUB>2</SUB>O<SUB>2</SUB> oxidation over the Br(1 wt%)-F(1 wt%)-Pd(5 wt%)/Al<SUB>2</SUB>O<SUB>3</SUB> catalyst in an aqueous acidic (H3PO4) medium have been thoroughly investigated. The effects of the O<SUB>2</SUB>/H<SUB>2</SUB> ratio, reaction temperature and acid concentration on the destruction of H<SUB>2</SUB>O<SUB>2</SUB> by its decomposition and/or hydrogenation reactions over the catalyst in the acidic reaction medium have also been studied. The net H<SUB>2</SUB>O<SUB>2</SUB> formation (H<SUB>2</SUB>O<SUB>2</SUB> yield) over the catalyst passed through a maximum with increasing the acid concentration, the temperature or the O<SUB>2</SUB>/H<SUB>2</SUB> feed ratio. However, it decreased markedly with increasing the gas space velocity or the reaction period. The H<SUB>2</SUB>O<SUB>2</SUB> decomposition and hydrogenation activities of the catalyst increased appreciably with increasing the reaction temperature and decreased with increasing the acid concentration. The H<SUB>2</SUB>O<SUB>2</SUB> destruction during the H<SUB>2</SUB>-to-H<SUB>2</SUB>O<SUB>2</SUB> oxidation increased with increasing the concentration of H<SUB>2</SUB> (relative to that of O<SUB>2</SUB>) due to the increased H<SUB>2</SUB>O<SUB>2</SUB> hydrogenation rate over the catalyst. The net H<SUB>2</SUB>O<SUB>2</SUB> formation in the H2-to-H<SUB>2</SUB>O<SUB>2</SUB> oxidation decreased sharply with increasing the initial amount of H2O2 present in the reaction mixture. The presence of H<SUB>2</SUB>O<SUB>2</SUB> and the higher H<SUB>2</SUB>/O<SUB>2</SUB> ratios have detrimental effects on the net formation of H<SUB>2</SUB>O<SUB>2