Synthesis, characterization and activity of Co and Ni catalysts supported on AlMe (Me?=?Zn, Zr, Ti) mixed oxides

Binary Al?CTi, Al?CZr and Al?CZn oxides, prepared by the sol?Cgel method were used as supports of catalytic systems. The catalysts were prepared by impregnation of these supports with the low cost Co or Ni nitrate salts and subsequent calcination at 700?°C. Catalysts have been characterized by S_BET, XRD and TPR techniques. The catalysts were tested in ethanol partial oxidation using a fixed-bed quartz reactor at atmospheric pressure and temperature at 600?°C. In test reactions a constant feed composition was used with O₂/EtOH molar ratio of 0.75 in nitrogen balance. The catalytic performance of the systems depends on type of support and type of promoter. Hydrogen and CO are the predominant products beside some by-products in different quantities (CO₂, methane, ethylene, acetaldehyde, acetone, acetic acid). The Co and Ni catalysts supported on AlZn binary oxide showed the highest selectivity to hydrogen and to carbon monoxide with full ethanol conversion. Selectivity of hydrogen follows the order of Co(Ni)AlZn?>?Co(Ni)AlTi?>?Co(Ni)AlZr. The best performance was obtained by NiAlZn catalyst with 89?% hydrogen selectivity.     

SEM–EDX and SAM–AES Investigations on Rochow Contact Masses

Appropriate Rochow contact masses have been investigated by the spatial resolution techniques SEM–EDX and SAM–AES. The results gave evidence of the existence and the catalytic action of (X-ray)-amorphous copper–silicon (Cu–Si) surface species, i.e. extremely highly dispersed particles or two-dimensional species. The well-known Rochow promoter zinc seems to act as a moderator rather than as a real accelerator. It ensures a stable rate for the reaction by neutralizing the detrimental action of silicon impurities. The silicon impurities make the whole of the silicon surface reactive and in this way cause a general blockade of the silicon surface by inactive copper species. Zinc localizes the reaction. The silicon surface remains partly free, and active Cu–Si surface species can be formed by lateral diffusion of copper onto the silicon surface that is still free. © 1997 by John Wiley & Sons, Ltd.     

On the estimation of wavelet coefficients

In wavelet representations, the magnitude of the wavelet coefficients depends on both the smoothness of the represented function f and on the wavelet. We investigate the extreme values of wavelet coefficients for the standard function spaces A_k=f| ∥f^k)∥₂ ≤ 1}, k∈N. In particular, we compare two important families of wavelets in this respect, the orthonormal Daubechies wavelets and the semiorthogonal spline wavelets. Deriving the precise asymptotic values in both cases, we show that the spline constants are considerably smaller. This revised version was published online in June 2006 with corrections to the Cover Date.     

Plasma deposition of thin films utilizing the anodic vacuum arc

Anodic vacuum arcs operating with cold cathodes in the spot mode and hot evaporating anodes are investigated to explore their technical potential as a plasma deposition technique. This discharge provides a unique source of a highly ionized, metal vapor plasma by autogeneration of the working gas to evaporation of the anode. This gas-free and droplet-free metal vapor plasma expands into the ambient vacuum (10^-4 mbar) and produces thin metallic films at the surface of substrates. An analysis of Al and Cu plasmas at the position of a possible substrate for arc currents between 20 and 200 A leads to the following results: electron densities, 10¹⁵-10¹⁸/ m³; degree of ionization, 0.5-25%; directed ion energy, 5 eV; and electron temperatures, 0.2-1 eV. Metallic coatings generated with deposition rates between 0.1 and 100 nm/s show the following properties: purity, 99.9%; polycrystalline structure with grain sizes between a few and a few hundred nm, same mass density as the respective bulk material, electrical conductivity rather close to that of the bulk material, and excellent optical properties. The coatings show good adhesion, which can be enhanced by a plasma-supported pretreatment of the substrate surface and by an acceleration of the ions towards the substrate     

Weighted Convergence of Lagrange Interpolation Based on Gauss-Kronrod Nodes

The Gauss-Kronrod quadrature scheme, which is based on the zeros of Legendrepolynomials and Stieltjes polynomials, is a standard rule for automaticnumerical integration in mathematical software libraries. For a long time,very little was known about the underlying Lagrange interpolationprocesses. Recently, the authors proved new bounds and asymptoticproperties for the Stieltjes polynomials and, subsequently, appliedthese results to investigate the associated interpolation processes. Thepurpose of this paper is to survey the quality of these interpolationprocesses, with additional results that extend and complete the existingones. The principal new results in this paper are necessary and sufficientconditions for weighted convergence. In particular, we show that theLagrange interpolation polynomials associated with the above interpolationprocesses have the same speed of convergence as the polynomials of bestapproximation in certain weighted Besov spaces.     

AlZn based Co and Ni catalysts for the partial oxidation of bioethanol — influence of different synthesis procedures

The catalytic performance of Co and Ni catalysts on AlZn mixed oxide supports depends on the synthesis procedure used for their preparation. For this study CoAlZn and NiAlZn catalysts were prepared by conventional sol-gel synthesis of the mixed oxide and subsequent impregnation of the support with the transition metal (SG = sol gel method) as well as by a single-step method were a gel is formed based on salts of all components using citric acid as chelating agent (CM = citrate method). The structure and morphology of the catalysts were characterized by nitrogen sorption, XRD and TPR measurements. They showed high activity in the partial oxidation of ethanol at 600–750 °C, but their properties depend on the preparation method. The higher performance of the catalysts prepared by the citrate method, where the transition metal is incorporated into the crystal structure of the support during preparation, is based on a change in morphology and structure, resulting in more active sites exposed on the surface. Compared to the Co catalysts, Ni catalysts showed a higher performance. This might be due to the higher reducibility and the smaller Ni particles size, which allows a better interaction with the support in NiAlZn catalysts.      

A rapid-scan device for the determination of spectral line profiles in pulsed discharges

The results of a time-of-flight experiment are presented, in which the total cross-sections for 2–400 eV positrons on H₂, D₂, N₂, and CO were measured.     

From complete to modulated synchrony in networks of identical Hindmarsh-Rose neurons

In most cases tendency to synchrony in networks of oscillatory units increases with the coupling strength. Using the popular Hindmarsh-Rose neuronal model, we demonstrate that even for identical neurons and simple coupling the dynamics can be more complicated. Our numerical analysis for globally coupled systems and oscillator lattices reveals a new scenario of synchrony breaking with the increase of coupling, resulting in a quasiperiodic, modulated synchronous state.     

Bestimmung der absoluten Übergangswahrscheinlichkeit der Linie C II 2511 Å

The transition probability of the CII line 2511 Å has been determined from relative intensity measurements of singly ionized carbon lines calibrated by the life time value of the 4² F ⁰-level obtained by the beam-foil method. The spectra were exposed from a quasistationary pulsed discharge between carbon electrodes in a helium-hydrogen mixture. Assuming LTE Saha's equation for C III/C II yielded the plasma temperature while the electron density was determined from theH _β profile. The transition probability of the line CII 1 324 Å was evaluated by the aid of the well-known life time of the² D ⁰-level.