A role of Au-content in performance of Pd-Au/SiO2 and Pd-Au/Al2O3 catalyst in the hydrogen and oxygen recombination reaction. The microcalorimetric and DFT studies

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 SiO2] and Al2O3 - 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 degrees 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/SiO2 (Pd90Au10) 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. (C) 2016 Elsevier B.V. All rights reserved.