Humidity induced deactivation of Al2O3 and SiO2 supported Pd, Pt, Pd-Pt catalysts in H2 + O2 recombination reaction: The catalytic, microcalorimetric and DFT studies

The thermal effects and activity of silica and alumina supported monometallic Pd, Pt and bimetallic Pd-Pt catalysts (of various Pd/Pt 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 pattern of changes in both the heat evolution and the conversion of hydrogen observed in the H-2/O-2 reaction seem to reflect the effect of water formation on the activity/deactivation of the studied catalysts. The catalysts have been prepared using the colloid-based reverse water-in-oil microemulsion method and characterized by XRD, XPS, SEM, EDS techniques. The recombination reaction of hydrogen and oxygen has been monitored using Microscal gas-flow through microcalorimeter as well as a laboratory flow microreactor. The humidity present in the reaction mixture and the water molecules formed in the recombination reaction both inhibited the activity of the tested catalysts. The nature of support and the type of metal played a role in such water-poisoning effect. Deactivation of alumina supported catalysts was stronger than silica supported counterparts and Pt was more prone to the water inhibition compared to Pd. The most promising catalysts exhibiting the lowest amount of evolved heat accompanied by high and stable activity are silica supported Pd-rich bimetallic Pd-Pt particles whereas alumina wash-coat-Pt is the catalyst of chose in the PAR reactors. The observed activity/water-poisoning relations found confirmation in the DFT calculations concerning the interactions between water molecules and mono-(Pd, Pt) as well as bi (Pd-Pt) metallic clusters as a function of cluster size and Pd/Pt compositions. (C) 2015 Elsevier B.V. All rights reserved.