Direct synthesis of hydrogen peroxide from H2 and O2 using Au–Pd/Fe2O3 catalysts

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Abstract
The direct synthesis of hydrogen peroxide from H2 and O2 using a range of Au, Pd and Au–Pd metal nanoparticles supported on iron oxide is described and discussed, and in particular the microstructure of the catalysts are investigated using a detailed electron microscopy study. Iron oxide was selected as a support because Au/Fe2O3 catalysts are known to be very active for low temperature CO oxidation. Hydrogen peroxide synthesis was investigated at low temperatures (2 °C) and short reaction (residence) time, and the addition of Pd to the Au catalyst was found to increase the rate of hydrogen peroxide synthesis as well as the concentration of hydrogen peroxide formed. Indeed the rates of hydrogen peroxide synthesis are higher for the Au–Pd alloy catalysts as compared to the Au or Pd only catalysts. These catalyst materials were also investigated for CO oxidation at 25 °C and all were found to be almost inactive. In contrast, Au-based catalysts that are very effective for low temperature CO oxidation were found to be totally inactive for H2 oxidation to H2O2. This suggests an inverse correlation between catalysts that are active for either CO or H2 activation. The microstructure of the Au–Pd/Fe2O3 catalysts was studied using scanning transmission electron microscopy and the metal alloy nanoparticles were found to have a core–shell morphology with Pd concentrated on the catalyst surface.