Direct oxidation of H₂ to H₂O₂ over Pd/Ga₂O₃ catalyst under ambient conditions: influence of halide ions added to the catalyst or reaction medium

Abstract

The formation of H₂O₂ from H₂ and O₂ and H₂O₂ decomposition/hydrogenation have been investigated in an acidic aqueous reaction medium over halide-assisted Pd/Ga₂O₃ catalyst system. The halide ions were introduced in the catalytic system by directly adding the halide ions to the reaction medium or by indirectly through the catalyst. The H₂O₂ formation selectivity was found to be influenced significantly with the addition of halide ions to the catalytic system. The H₂O₂ formation and H₂O₂ decomposition/hydrogenation studies over halide-modified Pd/Ga₂O₃ catalysts (pretreated under different gaseous atmosphere viz. air and nitrogen) revealed that bulk Pd oxidation state and nature of halide ions incorporated in the catalyst cooperatively promote the selective H₂O₂ formation. The decomposition and hydrogenation H₂O₂ on the Pd/Ga₂O₃ catalyst were also found strongly depend upon the nature of the halide ions introduced in the catalytic system. The selectivity for the conversion of H₂ to H₂O₂ was enhanced markedly due to the presence of Br^- ions in the catalytic system, irrespective of the bulk palladium oxidation state (Pd^O or Pd0) in the catalyst. The beneficial role of Br^-ions is attributed to the inhibition of the parallel H₂ to water oxidation and the consecutive H₂O₂ decomposition and hydrogenation reactions over the catalyst.