Applied Catalysis A: General 517 (2016) 196–210 Contents lists available at ScienceDirect Applied Catalysis A: General jou rn al hom epage: www.elsevier.com/locate/apcata A role of Au-content in performance of Pd-Au/SiO 2 and Pd-Au/Al 2 O 3 catalyst in the hydrogen and oxygen recombination reaction. The microcalorimetric and DFT studies E. Lalik, A. Drelinkiewicz ∗ , R. Kosydar, R. Tokarz-Sobieraj, M. Witko, T. Szumełda, J. Gurgul, D. Duraczy ´ nska Jerzy Haber Institute of Catalysis and Surface Chemistry, Niezapominajek 8, 30 239 Kraków, Poland a r t i c l e i n f o Article history: Received 9 October 2015 Received in revised form 3 March 2016 Accepted 4 March 2016 Available online 8 March 2016 Keywords: Hydrogen and oxygen recombination Pd-Au bimetallic particles Microcalorimetry a b s t r a c t The thermal effects and activity of silica and alumina supported bimetallic Pd-Au catalysts (of various Pd/Au ratio) in the exothermic H 2 and O 2 recombination reaction have been investigated in view of their potential use in the industrial passive autocatalytic recombiners (PAR). The catalysts were prepared by the colloid-based reverse “water-in-oil” microemulsion method which provided metal particles of size in a very narrow range (4–7 nm). In both SiO 2 and Al 2 O 3 − series catalysts the Pd-Au particles aggregated to some extent, especially strongly in alumina-series samples. The H 2 + O 2 reaction has been monitored using Microscal gas-flow through microcalorimeter at temperature of 22 ◦ C and atmospheric pressure. The observed pattern of changes in both the heat evolution and the conversion of hydrogen seem to reflect the effect of water and/or other oxygen-containing surface species (like OH) on the activity/deactivation of catalysts. The nature of support and the composition of metal particles (Pd/Au ratio) played a role. Deactivation of alumina supported catalysts was stronger than silica supported counterparts. Among all studied catalysts, the best behavior was offered by low Au content-containing Pd-Au-0.1/SiO 2 (Pd 90 Au 10 ) catalyst. Its almost stable activity during the catalytic run may be attributed to relatively weak interactions with water molecules and/or other oxygen-containing species (like OH), intermediates formed in the hydrogen oxidation. It may be supposed that electronic modification of palladium sites by gold assisted by the surface composition of Pd-Au particles reflecting in “surface arrangement of Pd and Au-atoms” are decisive. This experimental observation seems to correlated with the DFT calculation indicating that besides the number of Au atoms, their location with respect to the Pd, e.g “surface arrangement of Au” is more important for the energy/strength of interaction with water molecules. © 2016 Elsevier B.V. All rights reserved. 1. Introduction In water-cooled nuclear reactors, under normal and emergency operating conditions hydrogen is permanently released into air- filled containment atmosphere in radiolysis of water and water vapor-metal interactions. Several solutions have been consid- ered to reduce hydrogen concentration and the use of passive autocatalytic recombiners (PAR) is considered to be currently the most promising. In the PAR reactors hydrogen and oxy- gen is catalytically recombined according to exothermic reaction H 2 + 0.5O 2 = H 2 O + 240 kJ/mol. The existing PAR designs mostly use ∗ Corresponding author. E-mail address: ncdrelin@cyf-kr.edu.pl (A. Drelinkiewicz). stainless steel plates coated with an Pt or Pd − alumina wash coat [1,2]. The other types of catalysts Pd − spherical granules of ceramic carrier, Pt − cordierite in the shape of honeycomb and Pt-alumina wash coat − nickel foam are also reported [1–3]. However, at massive hydrogen release as in case of severe acci- dent, the recombiner can overheat and thus PAR reactors may become an ignition source itself. This problem has been studied mainly by the numerical simulation of hydrodynamic conditions and hydrogen mitigation [1,2,4–7]. From the operation of catalyst checked by hydrogen conversion together with the temperature of catalyst surface, the catalyst of high density of evenly distributed Pt particles on non-porous support is preferred [6]. The catalyst in the PAR reactor should fulfill a range of requirements, such as high resistance towards poisons, CO, CO 2 , CH 4 , iodine com- pounds as well as water vapor. Moreover, due to high exothermicity http://dx.doi.org/10.1016/j.apcata.2016.03.004 0926-860X/© 2016 Elsevier B.V. All rights reserved.