Direct Synthesis of Hydrogen Peroxide from H₂ and O₂ Using Al₂O₃ Supported Au−Pd Catalysts

Abstract

The direct synthesis of hydrogen peroxide from H 2 and O 2 using a range of alumina supported Au, Pd, and Au-Pd metal catalysts is described and discussed in detail for both fresh catalysts and materials that have been aged in storage. The conditions previously identified as being optimal for hydrogen peroxide synthesis (i.e., low temperatures (2°C) and short reaction residence times) are employed, and the effect of catalyst composition and preparation was investigated in detail for the fresh catalysts. The addition of Pd to the Au catalyst increases the rate of hydrogen peroxide synthesis as well as the concentration of hydrogen peroxide formed. Interestingly, the addition of relatively small amounts of Pd to the Au/Al 2 O 3 catalyst, replacing up to 20% of the Au, significantly increases the formation of hydrogen peroxide. The microstructure of the catalysts was studied using transmission electron microscopy and X-ray photoelectron spectroscopy for both the fresh and the aged catalyst, and the supported bimetallic particles were found to be of core-shell morphology with a Pd-rich surface. Hence, relatively little Pd is needed to induce the enhanced catalytic formation of hydrogen peroxide. Calcination at 400°C leads to the formation of stable reusable catalysts, whereas lower temperature pretreatments generate unstable catalysts that leach both Au and Pd into solution. Catalysts that have been aged in storage give an increase in activity for hydrogen peroxide synthesis by a factor of ca 3, and the relationship between the catalyst structure and this activity is discussed. The catalysts were also investigated for CO oxidation at 25°C, and all were found to be inactive or almost inactive; similarly, catalysts that are very effective for low-temperature CO oxidation were found to be totally inactive for H 2 oxidation to H 2 O 2 . This suggests an inverse correlation between catalysts that are active for either CO or H 2 activation, and this is commented on with respect to the mechanism.

Heterogeneous catalysts—discovery and design

“…Indeed, studies concerning the direct formation of hydrogen peroxide using Pd catalysts date back for almost a century. However, the combination of Au and Pd in supported alloys gave a synergistic enhancement in the activity and selectivity for both Au and Pd, [100][101][102][103][104][105][106][107][108] and this has now been demonstrated on many supports (Table 1). 105 Carbon and silica supports give the best performance as judged in terms of the yield of hydrogen peroxide that is achieved under these conditions.…”

“…Au/Al 2 O 3 catalysts were also observed to display activity in the direct formation of hydrogen peroxide by the reaction of H 2 and O 2 at low temperature. [100][101][102][103][104][105][106][107][108] However, this catalyst gave low selectivity based on H 2 utilisation and was much poorer in terms of catalyst performance when compared with supported Pd catalysts which had, up to that date, been studied for this reaction. Indeed, studies concerning the direct formation of hydrogen peroxide using Pd catalysts date back for almost a century.…”

Propylene epoxidation with in situ generated H2O2 in supercritical conditions

“…Nowadays, the catalytic processes which combine two or more consecutive reactions are being very attractive from sustainability point of view due to the reduction in the number of sub-processes associated to isolation and separation tasks of intermediate products [22]. Into this approach, the use of active and reusable bi-functional catalysts which contain metallic nanoparticles (NPs) embedded into inorganic oxide type-matrixes are currently being profusely considered for different catalytic processes [23,24,25].…”

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

“…[46] Supported Pd catalysts are the most widely investigated catalysts for the direct process, [3-30, 43, 44] but recent studies [31][32][33][34][35][36][37][38][39][40][41] revealed that supported bimetallic Au-Pd catalysts are the most effective for the direct route, as the addition of Au to Pd significantly enhances H 2 O 2 yield and selectivity. However, in common with supported Pd-only catalysts, supported bimetallic Au-Pd catalysts are also active for the undesired hydrogenation and decomposition of the H 2 O 2 once it has been formed.…”