Comparison of supports for the direct synthesis of hydrogen peroxide from H2 and O2 using Au-Pd catalysts

The direct synthesis of hydrogen peroxide from H-2 and O-2 using a range of supported Au-Pd alloy catalysts is compared for different supports using conditions previously identified as being optimal for hydrogen peroxide synthesis, i.e. low temperature (2 degrees C) using a water-methanol solvent mixture and short reaction time. Five supports are compared and contrasted, namely Al2O3, alpha-Fe2O3, TiO2, SiO2 and carbon. For all catalysts the addition of Pd to the Au only catalyst increases the rate of hydrogen peroxide synthesis as well as the concentration of hydrogen peroxide formed. Of the materials evaluated, the carbon-supported Au-Pd alloy catalysts give the highest reactivity. The results show that the support can have an important influence on the synthesis of hydrogen peroxide from the direct reaction. The effect of the methanol-water solvent is studied in detail for the 2.5 wt% Au-2.5 wt% Pd/TiO2 catalyst and the ratio of methanol to water is found to have a major effect on the rate of hydrogen peroxide synthesis. The optimum mixture for this solvent system is 80 vol.% methanol with 20 vol.% water. However, the use of water alone is still effective albeit at a decreased rate. The effect of catalyst mass was therefore also investigated for the water and water-methanol solvents and the observed effect on the hydrogen peroxide productivity using water as a solvent is not considered to be due to mass transfer limitations. These results are of importance with respect to the industrial application of these Au-Pd catalysts. (C) 2007 Elsevier B.V. All rights reserved.