Between the Vinča and Linearbandkeramik worlds: the diversity of practices and identities in the 54th–53rd centuries cal BC in south-west Hungary and beyond

Szederkény-Kukorica-dűlő is a large settlement in south-east Transdanubia, Hungary, excavated in advance of road construction, which is notable for its combination of pottery styles, variously including Vinča A, Ražište and LBK, and longhouses of a kind otherwise familiar from the LBK world. Formal modelling of its date establishes that the site probably began in the later 54th century cal BC, lasting until the first decades of the 52nd century cal BC. Occupation, featuring longhouses, pits and graves, probably began at the same time on the east and west parts of the settlement, the central part starting a decade or two later; the western part was probably abandoned last. Vinča pottery is predominantly associated with the east and central parts of the site, and Ražište pottery with the west. Formal modelling of the early history and diaspora of longhouses in the LBK world suggests their emergence in the Formative LBK of Transdanubia c. 5500 cal BC and then rapid diaspora in the middle of the 54th century cal BC, associated with the ‘earliest’ (älteste) LBK. The adoption of longhouses at Szederkény thus appears to come a few generations after the start of the diaspora. Rather than explaining the mixture of things, practices and perhaps people at Szederkény by reference to problematic notions such as hybridity, we propose instead a more fluid and varied vocabulary including combination and amalgamation, relationships and performance in the flow of social life, and networks; this makes greater allowance for diversity and interleaving in a context of rapid change

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Kinetic study of methanol oxidation o

Particle size effect: Methanol oxidation on supported Pt catalysts

The methanol oxidation was studied at two differently prepared supported Pt electrodes (Pt-C/GC and Pt/GC) in 0.5 M H2SO4 and 0.1 M NaOH. The supported Pt electrodes were characterized by AFM, STM TEM and HRTEM. The higher activity of Pt-C/GC than of Pt/GC catalyst, as well as negligible differences in the activities between the supported Pt catalysts and the corresponding single crystal electrodes oriented as the sites in the catalyst deposits in which Pt particles are dominant, clearly suggest the influence of the particle size effect on the catalyst activity

High activity of Pt4Mo alloy for the electrochemical oxidation of formic acid

Surface processes on Pt4Mo alloy well-defined by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) were studied in acid solution by cyclic voltammetry. It was established that Mo in the alloy is much more resistant toward electrochemical dissolution than pure Mo. During the potential cycling of Pt4Mo surfaces in completely quiescent electrolyte, hydrous Mo-oxide could be generated on Mo sites. Investigation of the formic acid oxidation revealed that this type of Mo-oxide enhances the reaction rate by more than I order of magnitude with respect to pure Pt. Surface poisoning by COads is significantly lower on Pt4Mo alloy than on pure Pt. The effect of hydrous Mo-oxide on the HCOOH oxidation rate was explained through the facilitated removal of the poisoning species and through its possible influence on the intrinsic rate of the direct reaction path

Insight into the Effect of Sn on CO and Formic Acid Oxidation at PtSn Catalysts

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, similar to 1.5 nm in diameter. Upon deposition on the carbon support, the particle size increases to similar 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 Pt3Sn 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 similar to 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 similar to 2 is 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 SnOHx moieties and SnO2 particles

Methanol electrooxidation in alkaline solutions on platinum-based electrodes: Classical and dynamical approach

The electrochemical oxidation of methanol has been carefully studied due to its application in fuel cells. In this work electrooxidation of methanol was investigated on bare platinum electrode, the platinum electrode covered with Nafion and platinum supported on zeolite 13X. Along with classical electrochemical methods, attractor reconstruction was used to make rough distinction among possible reaction mechanisms on different forms of Pt. The obtained transient voltammogram records were used to calculate apparent rate constants for methanol oxidation limiting steps in transient period. All samples contributed to methanol oxidation by basically same reaction mechanism, but with significantly different apparent rate constants