Decomposition and/or hydrogenation of hydrogen peroxide over Pd/Al<SUB>2</SUB>O<SUB>3</SUB> catalyst in aqueous medium: Factors affecting the rate of H<SUB>2</SUB>O<SUB>2</SUB> destruction in presence of hydrogen

Hydrogen peroxide destruction by its decomposition and/or hydrogenation to water in the presence of H<SUB>2</SUB> over Pd(5 wt.%)/Al<SUB>2</SUB>O<SUB>3</SUB> catalyst in an aqueous reaction medium, similar to that used in the H<SUB>2</SUB>-to-H<SUB>2</SUB>O<SUB>2</SUB> oxidation, has been thoroughly investigated at different reaction conditions. The H<SUB>2</SUB>O<SUB>2</SUB> destruction is strongly influenced by the oxidation state of Pd in the catalyst and also by the presence of different halide anions (viz. F<SUP>-</SUP>, Cl<SUP>-</SUP>, Br<SUP>-</SUP> and I<SUP>-</SUP>) in the acidic aqueous medium or in the catalyst, depending upon the concentration of halide anions. The cations associated with halide anions have, however, a little or no influence on the H<SUB>2</SUB>O<SUB>2</SUB> destruction. The iodide anions strongly poisoned the catalyst, even at their very low concentration. The fluoride anions have only a small effect on the H<SUB>2</SUB>O<SUB>2</SUB> destruction. The chloride or bromide anions drastically inhibit the rapid H<SUB>2</SUB>O<SUB>2</SUB> decomposition, but promote the slower H<SUB>2</SUB>O<SUB>2</SUB> hydrogenation. The H<SUB>2</SUB>O<SUB>2</SUB> destruction reactions are strongly influenced by the halide anion and acid concentrations. The presence of acid (protons) plays a very important role in drastically reducing the H<SUB>2</SUB>O<SUB>2</SUB> destruction, particularly in the presence of chloride anions. Both in the presence and absence of Cl<SUP>-</SUP> or Br<SUP>-</SUP> anions, the H<SUB>2</SUB>O<SUB>2</SUB> destruction activity of the catalyst is markedly reduced because of the oxidation of Pd but it is drastically increased due to the presence of H<SUB>2</SUB>. A plausible reaction mechanism for the rapid H<SUB>2</SUB>O<SUB>2</SUB> decomposition and slower H<SUB>2</SUB>O<SUB>2 </SUB>hydrogenation reactions, prevailing under the different reaction conditions, has also been discussed