Catalysis Today 248 (2015) 40–47 Contents lists available at ScienceDirect Catalysis Today j o ur na l ho me page: www.elsevier.com/locate/cattod The effect of the metal precursor-reduction with hydrogen on a library of bimetallic Pd-Au and Pd-Pt catalysts for the direct synthesis of H 2 O 2 Stefano Sterchele a,b,∗ , Pierdomenico Biasi b,c , Paolo Centomo a , Sandro Campestrini a , Andrey Shchukarev c , Anne-Riikka Rautio d , Jyri-Pekka Mikkola b,c , Tapio Salmi b , Marco Zecca a,∗ a Dipartimento di Scienze Chimiche, Università degli Studi di Padova via Marzolo 8, I35131 Padova, Italy b Department of Chemical Engineering, Laboratory of Industrial Chemistry and Reaction Engineering, Process Chemistry Centre (PCC), Åbo Akademi University, Biskopsgatan 8, FI-20500 Åbo-Turku, Finland c Department of Chemistry, Technical Chemistry, Chemical-Biochemical Centre (KBC), Umeå University, UMEÅ, SE-90187, Sweden d Department of Electrical Engineering, Faculty of Technology, Microelectronics and Materials Physics Laboratories, EMPART Research Group of Infotech Oulu, University of Oulu, FI-90014 Oulu, Finland a r t i c l e i n f o Article history: Received 27 November 2013 Received in revised form 30 January 2014 Accepted 13 February 2014 Available online 16 March 2014 Keywords: Bimetallic Pd-Pt catalysts Pd-Au catalysts H2O2 Direct Synthesis a b s t r a c t Two sets of bimetallic Pd-Pt (Pd: 1.0; Pt: 0.25-1.0%, w/w) and Pd-Au (Pd: 1.0; Au: 0.25-1.0%, w/w) catalysts have been used, with no added promoter, in the catalytic direct synthesis (CDS) of hydrogen peroxide from its elements at 2 ◦ C with a CO 2 /O 2 /H 2 mixture (72/25.5/2.5%, respectively). The catalysts were sup- ported on the commercial macroreticular ion-exchange resin Lewatit K2621 and were obtained from the reduction with H 2 of ion-exchanged cationic precursors at 5 bar and at 60 ◦ C. The addition of Pt or Au to Pd produced an increase of the initial overall catalytic activity in comparison with monometallic Pd with both the second metals, but with Pt the increase was much higher than with Au. Moreover, the addition of 0.25% (w/w) Pt, or more, invariably made all the Pd-Pt catalysts less selective with respect to Pd alone. In the case of Au, by contrast, the addition of 0.25% w/w produced an increase, albeit small, of the selectivity. As the result, the most active and productive Pd-Pt catalyst was 1Pd025PtK2621 with 1891 mol (H 2 ) mol -1 (Pd+Pt) h -1 initially consumed, 1875 mol (H 2 O 2 ) mol -1 (Pd+Pt) h -1 initially produced, a 45% selectivity towards H 2 O 2 at 50% conversion of H 2 . In the case of the Pd-Au bimetallic catalysts, 1Pd025AuK2621 was the best one, with 1184 mol (H 2 ) mol -1 (Pd+Pt) h -1 initially consumed, 739 mol (H 2 O 2 ) mol -1 (Pd+Pt) h -1 initially produced, a 55% selectivity towards H 2 O 2 at 50% conversion of H 2 . Although the characterization of the Pd-Pt and Pd-Au catalysts with TEM showed that the morphology of the nanostructured metal phases in the Pd-Pt and Pd- Au catalysts was very different from each family to the other, no clear correlation between the size of the nanoparticles and their distribution and the catalytic performance was apparent. These catalysts were also generally different, especially the Pd-Au ones, from previously reported related materials obtained from the same support and the same precursor, but with a different reducing agent (formaldehyde). © 2014 Elsevier B.V. All rights reserved. 1. Introduction H 2 O 2 is a desirable clean oxidant for many chemical applica- tions, but its industrial use is limited due to its high cost. The ∗ Corresponding author at: Department of Chemical Engineering, Laboratory of Industrial Chemistry and Reaction Engineering, Process Chemistry Centre (PCC), Åbo Akademi University, Biskopsgatan 8, FI-20500 Åbo-Turku, Finland; Dipartimento di Scienze Chimiche, Università degli Studi di Padova via Marzolo 8, I35131 Padova, Italy. E-mail addresses: ssterche@abo.fi (S. Sterchele), marco.zecca@unipd.it (M. Zecca). catalytic direct synthesis (CDS) from H 2 /O 2 with catalysts based on Pd could potentially lower the cost to less than half its cur- rent value and make the use of H 2 O 2 feasible for processes such as primary and waste water treatments, cleaning of semiconductors and oxidations in industrial chemical synthesis [1]. The CDS is only seemingly a simple reaction, because several side-reactions (Scheme 1) yield water, the most stable molecule in the reaction network, and adversely affect the selectivity. The latter typically decreases with H 2 conversion, limiting the final concentration of H 2 O 2 . Safety is also a critical issue in the CDS, because H 2 /O 2 mix- tures are explosive in a wide composition range (4–96%, v/v). Due to its higher cost, H 2 is usually the limiting reagent and for safety reasons it is generally very diluted in the reaction mixture [2]. This http://dx.doi.org/10.1016/j.cattod.2014.02.021 0920-5861/© 2014 Elsevier B.V. All rights reserved.