The role of the support in achieving high selectivity in the direct formation of hydrogen peroxide

Abstract

Pd-only, Au-only and bimetallic AuPd catalysts supported on a range of supports (Al₂O₃, TiO₂, MgO, and C) have been prepared by impregnation and tested for the hydrogenation and decomposition of hydrogen peroxide under conditions similar to those used in direct synthesis of hydrogen peroxide. Hydrogenation and decomposition are the main pathways for loss of selectivity and yield in the direct synthesis reaction, and the support is found to be a crucial parameter with respect to hydrogenation and decomposition activity. We show that by making the right choice of support for both the monometallic and bimetallic Au and Pd catalysts, it is possible to achieve very low hydrogen peroxide hydrogenation and decomposition activity, thus enhancing hydrogen peroxide productivity during synthesis. Carbon is found to be the optimal support for both monometallic Au and Pd catalysts as well as Au–Pd alloys, since carbon-supported catalysts gave the lowest hydrogenation and decomposition activities. Au-only catalysts were generally less active than Pd-only catalysts when utilizing the same support and metal loading. The addition of Au to Pd catalysts supported on TiO₂ and carbon resulted in a decrease in both H₂O₂ hydrogenation and decomposition while the reverse effect was observed for the Al₂O₃ and MgO-supported catalysts. These effects are discussed in terms of the basicity of the support, and in particular the isoelectronic point of the support, which is a major factor in controlling the stability of hydrogen peroxide under reaction conditions.