Direct synthesis of hydrogen peroxide from H2 and O2 using TiO2-supported Au-Pd catalysts

The direct synthesis of H2O2 at low temperature (2 °C) from H2 and O2 using TiO2-supported Au, Pd, and Au-Pd catalysts is discussed. The Au-Pd catalysts performed significantly better than the pure Pd/TiO2 and Au/TiO2 materials. Au-Pd particles were found with a core-shell structure, with Pd concentrated on the surface. The highest yields of H2O2 were observed with uncalcined catalysts, but these were particularly unstable, losing both metals during use. In contrast, samples calcined at 400 °C were stable and could be reused several times without loss of performance. These catalysts exhibited low activity for CO oxidation at 25 °C; conversely, catalysts effective for low-temperature CO oxidation were inactive for H2 oxidation to H2O2. This anticorrelation is explored in terms of the mechanism by which the catalysts function and the design of catalysts for the selective oxidation of one of these substrates in the presence of the other.