The Effect of Bromide Pretreatment on the Performance of Supported Au–Pd Catalysts for the Direct Synthesis of Hydrogen Peroxide

Abstract

AbstractThe effect of pretreating Au–Pd catalysts on MgO and C supports with aqueous bromide solution, prior to using them for the direct synthesis of hydrogen peroxide, has been investigated. These two supports were selected since the parent materials exhibit contrasting microstructures and activities. The carbon‐supported catalysts comprise homogeneous Au–Pd alloy nanoparticles, which give high activity, whereas the MgO‐supported catalyst has Au–Pd alloys with a Pd‐rich surface and a Au‐rich core, which result in lower activity. Pretreatment of these catalysts with bromide was found to enhance H2O2 productivity and the degree of enhancement was largely dependent on the nature of the Au–Pd nanoparticles. Whereas bromide pretreatment significantly enhanced H2O2 productivity over the MgO‐based catalysts, the carbon‐based catalyst only showed a subtle promotional effect. Very low loadings of bromide (0.00034–0.044 wt %) were required to yield a significant positive effect. Higher bromide loadings (0.5–8.3 wt %) proved deleterious. The promotional effect has been correlated to selective poisoning of sites responsible for H2O2 hydrogenation and decomposition. In view of the limited effect of bromide pretreatment on the yield of H2O2 coupled with the effective performance of the carbon supported Au‐Pd catalysts in the absence of halides, for practical processes the addition of halides is not considered advisable with this catalyst system.