Three different CoMn/γ-Al2O3 catalysts were prepared by the incipient wetness impregnation route and compared to a Co/γ-Al2O3 catalyst. The effect of co-impregnation vs. sequential impregnation as well as the order of component addition was investigated. All catalysts were characterised by TPR, H2-chemisorption, XRD and XPS and their activity and selectivity in the Fischer-Tropsch reaction was investigated. Complementary, self-consistent DFT calculations were performed to further address the observed promotion effects. All Mn promoted catalysts displayed heightened intrinsic activity, heightened selectivity to light olefins and C5+ species and lowered selectivity to CH4 compared to Co. The promotion effects on selectivity and intrinsic activity were found to be independent on catalyst preparation method. The catalysts undergo a restructuring during operation, in which an excess of Mn saturates the catalytically relevant sites causing the similar behaviour. The Co-specific activity differed between the Mn promoted catalysts. This was attributed to varying degrees of Mn incorporation in the Co3O4 particles, causing different degrees of reduction limiting the available metallic Co surface area. The DFT calculations suggested that the binding energy for all investigated species increases on Co in the presence of Mn, facilitating CO dissociation which can explain the higher intrinsic activity. The affected selectivities for olefins, C5+ and CH4 can all be attributed to an inhibited hydrogenation activity demonstrated by the increased barriers for CH3 and CH4 formation.

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The hydrogen solubility and permeation in Pd77%Ag23% membranes have been determined as a function of temperature and membrane thickness. Unexpectedly, the solubility of hydrogen is found to systematically increase as the membrane thickness decreases from 11.2 to 2.2 µm. Topography studies by atomic force microscopy in conjunction with previously reported characterization suggest linkage of the hydrogen solubility to the density of grain boundaries. A higher average grain boundary density for thinner membranes results from the nucleation and growth proceeding during membrane fabrication by sputtering. For the membranes and conditions (no membrane pretreatment; 300-400°C; Δp H2 ≤ 2 bar) applied here, surface phenomena affect the hydrogen transport at thicknesses below ~5 µm.Determination of the solubility constants hence allowed extraction of the bulk diffusivity 2 parameters from the permeability measurements over the thicker membranes (6.7-11.2 µm), in good agreement with reported values obtained using other techniques.

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Antimony-doped tin dioxide (ATO) is considered a promising support material for Pt-based fuel cell cathodes, displaying enhanced stability over carbon-based supports. In this work, the effect of Sb segregation on the conductance and catalytic activity at Pt/ATO interface was investigated through a combined computational and experimental study. It was found that Sb-dopant atoms prefer to segregate toward the ATO/Pt interface. The deposited Pt catalysts, interestingly, not only promote Sb segregation, but also suppress the occurrence of Sb(3+) species, a charge carrier neutralizer at the interface. The conductivity of ATO was found to increase, to a magnitude close to that of activated carbon, with an increment of Sb concentration before reaching a saturation point around 10%, and then decrease, indicating that Sb enrichment at the ATO surface may not always favor an increment of the electric current. In addition, the calculation results show that the presence of Sb dopants in ATO has little effect on the catalytic activity of deposited three-layer Pt toward the oxygen reduction reaction, although subsequent alloying of Pt and Sb could lower the corresponding catalytic activity. These findings help to support future applications of ATO/Pt-based materials as possible cathodes for proton exchange membrane fuel cell applications with enhanced durability under practical applications.