Supported Catalysts DOI: 10.1002/anie.201308067 The Direct Synthesis of Hydrogen Peroxide Using Platinum-Promoted Gold–Palladium Catalysts** JenniferK. Edwards,* James Pritchard, Li Lu, Marco Piccinini, Greg Shaw, Albert F. Carley, David J. Morgan, Christopher J. Kiely, and Graham J. Hutchings* Abstract: The direct synthesis of hydrogen peroxide offers a potentially green route to the production of this important commodity chemical. Early studies showed that Pd is a suitable catalyst, but recent work indicated that the addition of Au enhances the activity and selectivity significantly. The addition of a third metal using impregnation as a facile preparation method was thus investigated. The addition of a small amount of Pt to a CeO 2 -supported AuPd (weight ratio of 1:1) catalyst significantly enhanced the activity in the direct synthesis of H 2 O 2 and decreased the non-desired over-hydrogenation and decomposition reactions. The addition of Pt to the AuPd nanoparticles influenced the surface composition, thus leading to the marked effects that were observed on the catalytic formation of hydrogen peroxide. In addition, an experimental approach that can help to identify the optimal nominal ternary alloy compositions for this reaction is demonstrated. The direct synthesis of hydrogen peroxide from hydrogen and oxygen offers a cleaner, more atom-efficient alternative to the current commercial production process for this important commodity chemical. Currently, over three million metric tons of H 2 O 2 are produced from the indirect anthra- quinone process, around 80% of this amount is used for fine chemical synthesis and in the paper and textile bleaching industries. [1] The increasing demand for propylene oxide means that the forecasted demand for H 2 O 2 is predicted to exceed 4.3 million metric tons in 2015. [2] The indirect process produces concentrated H 2 O 2 that has to be transported to its point of use where it is diluted. The direct route would enable H 2 O 2 production to take place at its point of use, and for this reason there is significant interest in developing such a catalytic process. [3] An obvious challenge in the direct synthesis process is achieving high H 2 selectivity toward H 2 O 2 and avoiding water formation by the sequential hydrogena- tion of H 2 O 2 . A number of catalysts have been investigated for the direct synthesis of H 2 O 2 . The vast majority of them are based on supported Pd nanoparticles, [3b, 4] but these materials require the addition of acid and halide promoters in the reaction medium to achieve high selectivity at high conver- sions. [3b, 4d, 5] We have shown that the incorporation of Au in Pd catalysts to form supported nanoalloys results in catalysts that synthesize H 2 O 2 with high selectivities in the absence of acid and halide stabilizers. [6] Clearly, the composition of the alloy catalyst is a major factor in catalyst design. [6a, 7] Recently, we have shown that the addition of Pt to the AuPd nanoalloy catalyst to form a trimetallic alloy has beneficial effects in the oxidation of benzyl alcohol. [8] The use of Pt as a catalyst component in the direct synthesis process has also been considered previously by Strukul and co-workers. [9] They synthesized Pd/Pt and Pd/Au nanoparticles supported on sulphated zirconia and compared the activity for the direct synthesis of H 2 O 2 in the presence of acid. The addition of Pt to Pd enhanced the yield of H 2 O 2 , but the extent of the effect was highly sensitive to the concentration of Pt : by using a low Pt content it was possible to improve the H 2 selectivity from 55 to 70 %. However, the positive effect on H 2 O 2 selectivity was not observed by Lunsford et al., [4c] who showed that the addition of 5 atom % Pt to a SiO 2 -supported Pd (0.5 wt %) catalyst increased the H 2 O 2 productivity by a factor of 2.5, but the selectivity was slightly lower than that of the monome- tallic Pd catalyst. This effect may be due to the presence of halide in the Lunsford study, and indeed, when halide was absent, the Pt/Pd catalysts produced only water. Clearly, the addition of Pt can have beneficial effects as a catalyst component in the direct-synthesis process. Herein we show that the addition of Pt to CeO 2 -supported AuPd nanoalloy catalysts to form trimetallic catalysts can have marked effects on both the synthesis and hydrogenation of H 2 O 2 , and we demonstrate an experimental approach to identify the optimal nominal trimetallic catalyst composition for the synthesis of H 2 O 2 . We prepared catalysts with 5 wt% total metal content using an impregnation method [6d] and selected CeO 2 as a support, as we had previously shown this to be a suitable support material for AuPd nanoalloys. [10] A series of CeO 2 - supported mono- and bimetallic Au, Pd, and Pt catalysts were prepared—we have shown in our earlier study that the AuPdPt trimetallic compositions on TiO 2 or activated carbon supports form alloys containing all three component metals. [8] The monometallic and bimetallic combinations of these catalysts were evaluated for the direct synthesis of H 2 O 2 , and the results for the initial rates after 2 min reaction and also for a standard reaction time of 30 min are shown in Table 1. The activities ranked in the order PdPt > Pd > [*] Dr. J. K. Edwards, J. Pritchard, M. Piccinini, G. Shaw, Dr. A. F. Carley, D. J. Morgan, Prof. G. J. Hutchings Cardiff Catalysis Institute, School of Chemistry Cardiff University, Main Building Park Place, Cardiff, CF10 3AT (UK) E-mail: edwardsjk@cf.ac.uk hutch@cf.ac.uk L. Lu, Prof. C. J. Kiely Department of Materials Science and Engineering Lehigh University 5 East Packer Ave, Bethlehem, PA 18015 (USA) [**] We thank Solvay S.A. for financial support. Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/anie.201308067. A ngewandte Chemi e 1 Angew. Chem. Int. Ed. 2014, 53,1–5  2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim These are not the final page numbers! Ü Ü