Acetylene and ethylene hydrogenation on alumina supported Pd–Ag model catalysts

Adsorption and co-adsorption of ethylene, acetylene and hydrogen on Pd-Ag particles, supported on thin alumina films, have been studied by temperature programmed desorption (TPD). The TPD results show that adding of Ag to Pd suppresses overall hydrogenation activity but increases selectivity towards ethylene, i.e. similar to that observed on real catalysts. The results are rationalized on the basis of a complex interplay between surface and subsurface hydrogen species available in the system, whereby the latter species are the most critical for total hydrogenation of acetylene to ethane

Highly Stable and Reactive Platinum Single Atoms on Oxygen Plasma-Functionalized CeO₂ Surfaces: Nanostructuring and Peroxo Effects

Atomically dispersed precious metals on oxide supports have recently become increasingly interesting catalytic materials. Nonetheless, their non-trivial preparation and limited thermal and environmental stability constitutes an issue for their potential applications. Here we demonstrate that an oxygen plasma pre-treatment of the ceria (CeO2 ) surface serves to anchor Pt single atoms, making them active and resistant towards sintering in the CO oxidation reaction. Through a combination of experimental results obtained on well-defined CeO2 films and theory, we show that the O2 plasma causes surface nanostructuring and the formation of surface peroxo (O22-) species, favoring the uniform and dense distribution of isolated strongly bonded Pt2+ atoms. The promotional effect of the plasma treatment was further demonstrated on the powder Pt/CeO2 catalysts. We believe that plasma functionalization can be applied to other metal/oxide systems to achieve tunable and stable catalysts with a high density of active sites

Highly Stable and Reactive Platinum Single Atoms on Oxygen Plasma-Functionalized CeO₂ Surfaces: Nanostructuring and Peroxo Effects

Atomically dispersed precious metals on oxide supports have recently become increasingly interesting catalytic materials. Nonetheless, their non-trivial preparation and limited thermal and environmental stability constitutes an issue for their potential applications. Here we demonstrate that an oxygen plasma pre-treatment of the ceria (CeO2 ) surface serves to anchor Pt single atoms, making them active and resistant towards sintering in the CO oxidation reaction. Through a combination of experimental results obtained on well-defined CeO2 films and theory, we show that the O2 plasma causes surface nanostructuring and the formation of surface peroxo (O22-) species, favoring the uniform and dense distribution of isolated strongly bonded Pt2+ atoms. The promotional effect of the plasma treatment was further demonstrated on the powder Pt/CeO2 catalysts. We believe that plasma functionalization can be applied to other metal/oxide systems to achieve tunable and stable catalysts with a high density of active sites

Oxide nanotemplates for self-assembling "solid" building blocks

It is widely accepted that self-assembling building blocks is one of the promising ways for engineering new materials. Recent years reveal substantial progress in fabricating colloidal particles, polymer blocks and supramolecular aggregates of organic molecules. Despite of substantial progress in molecular self-assembly there is still a lack of simple blocks made of "solid matter" (e.g. metals, oxides etc.) with well-defined crystal structure and spatial order. Here we demonstrate that ordered arrays of metal nanoclusters can be fabricated by self-assembly on a wide range of oxide templates. These nano-templates are produced either by depositing an alien oxide film or by oxidizing a metal/metal oxide substrate.Comment: 11 pages, 2 figures added DFT calculations and Fig.

Surface - Active and Complexforming Copolymers of Sodium 2-acrylamido-2-methylpropanesulfonate with Ethyleneglycol Vinyl Ether

A new water-soluble polyelectrolyte - the copolymer of sodium 2-acrylamido-2-methylpropanesulfonate and ethylene glycol vinyl ether has been synthesized by free-radical copolymerization in aqueous medium. Synthesis of the linear structure water-soluble copolymer of sodium 2-acrylamido-2-methylpropanesulfonate (Na-AMPS) and ethylene glycol vinyl ether (EGVE) has been confirmed by IR spectroscopy method, potentiometric titration and viscometer. The concentration behavior of the reduced viscosity of copolymer solutions that is typical for polyelectrolytes has been revealed. The reactivity ratios for the copolymerization of the monomers estimated by the Mayo–Lewis method have indicated lower reactivity of ethylenglycol vinyl ether in comparison with sodium 2-acrylamido-2-methylpropanesulfonate. Also it was shown the decrease of reaction’s relative rate with an increase of molar fraction of EGVE in the initial mixture of monomers. Adsorption at the air-water solution interface was studied by measure of surface tension (σ) in order to determine the surface properties of new copolymers of ethyleneglycol vinyl ethers – sodium 2-acrylamido- 2-methylpropanesulfonate. It was shown that copolymers of sodium 2-acrylamido-2-methylpropanesulfonate and ethylenglycol vinyl ether have higher surface activity compared to sodium 2-acrylamido-2-methylpropanesulfonate homopolymer. The isotherm of copolymer’s surface tension based on equilibrium value of σ was constructed together with the isotherm of surface tension water solution poly- Na-AMPS. Based on isotherms the surface activity on Rebinder (GRe) for poly- Na-AMPS and copolymer Na-AMPS-EGVE was determined. The values of polymer’s standard free energy of adsorption (ΔadsG0298) were calculated in order to identify the causes and mechanism of change in surface activity and adsorption. Results show that the gain in standard free energy adsorption in the transition from homopolymer to copolymer Na-AMPS-EGVE is about 4 kJ/base-mole. Interpolymer reaction of the Na-AMS–EGVE copolymer with poly- N,N-dimethyl-N,N-diallylammonium chloride (PMAAC) has been studied. Higher surface activity of mixtures of copolymer and PMAAC than of individual polyelectrolytes was discovered. This effect testified to the formation of interpolymer complex of the Na-AMS–EGVE copolymer with polycations due to electrostatic interactions

Spatial patterns and cell surface clusters in perineuronal nets

© 2016 Elsevier B.V.Perineuronal nets (PNN) ensheath GABAergic and glutamatergic synapses on neuronal cell surface in the central nervous system (CNS), have neuroprotective effect in animal models of Alzheimer disease and regulate synaptic plasticity during development and regeneration. Crucial insights were obtained recently concerning molecular composition and physiological importance of PNN but the microstructure of the network remains largely unstudied. Here we used histochemistry, fluorescent microscopy and quantitative image analysis to study the PNN structure in adult mouse and rat neurons from layers IV and VI of the somatosensory cortex. Vast majority of meshes have quadrangle, pentagon or hexagon shape with mean mesh area of 1.29 µm2 in mouse and 1.44 µm2 in rat neurons. We demonstrate two distinct patterns of chondroitin sulfate distribution within a single mesh – with uniform (nonpolar) and node-enriched (polar) distribution of the Wisteria floribunda agglutinin-positive signal. Vertices of the node-enriched pattern match better with local maxima of chondroitin sulfate density as compared to the uniform pattern. PNN is organized into clusters of meshes with distinct morphologies on the neuronal cell surface. Our findings suggest the role for the PNN microstructure in the synaptic transduction and plasticity

Partial oxidation of ethanol on vanadia catalysts on supporting oxides with different redox properties compared to propane

The influence of the support material of vanadia catalysts on the reaction rate, activation energies, and defect formation enthalpies was investigated for the oxidative dehydrogenation of ethanol and propane. Characterization by infrared absorption–reflection spectroscopy (IRAS), Raman and UV–vis spectroscopy verifies a high dispersion of vanadia for powder and thin-film model catalysts. The support effect of ceria, alumina, titania, and zirconia is reflected in activation energy, oxidative dehydrogenation (ODH) rate, and temperature-programmed reductions (TPR) for both catalyst systems, ethanol and propane. Impendence spectroscopy and density functional theory (DFT) calculations were used to determine the defect formation enthalpy of the vanadyl oxygen double bond, providing the scaling parameter for a Bell–Evans–Polanyi relationship. On the basis of a Mars–van-Krevelen mechanism, an energy profile for the oxidative dehydrogenation is proposed