The role of Sn on the catalytic activity for CO and formic acid oxidation is studied by comparing the activities of differently treated PtSn/C and Pt/C catalysts. The catalysts are prepared by a microwave-assisted polyol synthesis method. As revealed by scanning tunneling and transmission electron microscopic (STM and TEM) characterization, the outcomes of the synthesis procedure for both Pt and PtSn are small particles, ∼1.5 nm in diameter. Upon deposition on the carbon support, the particle size increases to ∼2.5 nm due to sintering. X-ray diffraction (XRD) analysis shows that PtSn/C has a low alloying degree and is mainly composed of Pt and Pt 3 Sn phases. The remaining Sn is present in the form of very small tin oxide particles. Different surfaces are obtained by double-layer, oxide, and CO annealing of the Pt/C and PtSn/C catalysts and by modifying the CO-annealed surfaces with irreversibly adsorbed tin, Sn irr . The presence of Sn in any form (oxide, alloyed, or Sn irr ) on the surface shifts the onset potential for the CO oxidation negatively by more than 0.4 V in comparison to equivalently treated Pt/C catalysts. For the CO-annealed PtSn/C catalyst, a so-called skeleton structure, Sn is present only in the subsurface layers. The subsurface Sn has a mild effect on the CO activity, and hence the onset potential is only marginally shifted to cathodic potentials by ∼50 mV compared to that on Pt/C. The formic acid oxidation is enhanced at any of the PtSn/C surfaces with Sn in the surface layer. The activity enhancement is explained by a reduced CO poisoning of the surface Pt sites. As a consequence, the current is not entering plateau as on the Pt/C catalysts. Furthermore, the skeleton PtSn/C is ∼2 times more active than similarly treated Pt/C. The results have been substantiated and explained by comprehensive density functional theory (DFT) simulations. The DFT results indicate that the increased oxidation rates are not only due to surface Sn but also due to a weakened CO binding in the vicinity of the surface SnOH x moieties and SnO 2 particles.

epoc ABSTRACT: 1 H NMR spectroscopy was used to investigate hydrogen bonding in the structurally related (Z)-and (E)-5-substituted-2-alkylidene-4-oxothiazolidines in polar and apolar solvents. The equilibrated mixtures of these typical push-pull alkenes consist of the intramolecularly H-bonded E-isomer and intermolecularly H-bonded Z-isomer in varying proportions which depend on the solvent polarity. For a representative of the series, (E)-(5-ethoxycarbonylmethyl-4-oxothiazolidin-2-ylidene)-1-phenylethanone (1), the lack of a concentration and temperature dependence of the large chemical NH shift ( 12.06 ppm) in CDCl 3 indicates strong intramolecular resonance-assisted hydrogen-bond formation (RAHB). The upfield chemical shifts of the NH proton of the (Z)-1 isomer as a function of temperature increase and the large 1 H NMR Á/ÁT value (À11.82 ppb C À1 , Z/E

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Ni–Co alloy deposits and their parent metals were formed on Cu substrates by electrolysis under different current densities applied in the galvanostatic regime. A quantitative scanning electron microscopy technique was employed to study the morphology and surface roughness of the obtained deposits. The structure of the deposits is governed by the nature of depositing ions and quantity of evolved hydrogen. The cauliflower morphology and the highest mean surface roughness values are the results of electrodeposition from the Ni containing bath. The structure of the Co deposits formed under the same conditions and determined by the formation of the hexagonal close-packed phase results in a more uniform grain size distribution and formation of smoother platelet deposits. The mean surface values of the parent metals are independent of the current density. The dendritic growth is a special case of a structure formed only in the Ni–Co alloy deposition at selected, high current densities of 220 and 400mAcm−2 . The dendrites obtained at a higher current density of 400mAcm−2 have shown more developed structures with smaller dendrites that have more pronounced secondary branch and high order branches.