Cornelia Breitkopf

Selective Modification of the Acid–Base Properties of Ceria by Supported Au

Au supported on CeO(2) prepared by deposition-precipitation with urea leads to a basic catalyst. Au acts in two ways as surface modifier. First, Au selectively interacts with Ce(4+) cations by either blocking access to or reducing Ce(4+) to Ce(3+). Second, the resulting Au atoms (presumably as Au(+) ions) act as soft, weak Lewis acid sites stabilizing carbanion intermediates and enhancing hydride abstraction in the dehydrogenation of alcohols. In consequence, the thus-synthesized basic catalyst catalyzes the dehydrogenation of propan-2-ol to acetone with high efficiency and without notable deactivation. Additionally, the dehydration pathway of propan-2-ol is eliminated, as Au also quantitatively blocks access to strongly acidic Ce(4+) ions or reduces them to Ce(3+).

Activation and isomerization of n-butane on sulfated zirconia model systems—an integrated study across the materials and pressure gaps

Butane activation has been studied using three types of sulfated zirconia materials, single crystalline epitaxial films, nanocrystalline films, and powders. A surface phase diagram of zirconia in interaction with SO(3) and water was established by DFT calculations, which was verified by LEED investigations on single-crystalline films and by IR spectroscopy on powders. At high sulfate surface densities a pyrosulfate species is the prevailing structure in the dehydrated state; if such species are absent, the materials are inactive. Theory and experiment show that the pyrosulfate can react with butane to give butene, H(2)O and SO(2), hence butane can be activated via oxidative dehydrogenation. This reaction occurred on all investigated materials; however, isomerization could only be proven for powders. Transient and equilibrium adsorption measurements in a wide pressure and temperature range (isobars measured via UPS on nanocrystalline films, microcalorimetry and temporal analysis of products measurements on powders) show weak and reversible interaction of butane with a majority of sites but reactive interaction with <5 micromol g(-1) sites. Consistently, the catalysts could be poisoned by adding sodium to the surface in a ratio S/Na = 35. Future research will have to clarify what distinguishes these few sites.

The impact of microstructure geometry on the mass transport in artificial pores: a numerical approach

The microstructure of porous materials used in heterogeneous catalysis determines the mass transport inside networks, which may vary over many length scales. The theoretical prediction of mass transport phenomena in porous materials, however, is incomplete and is still not completely understood. Therefore, experimental data for every specific porous system is needed. One possible experimental technique for characterizing the mass transport in such pore networks is pulse experiments. The general evaluation of experimental outcomes of these techniques follows the solution of Ficks second law where an integral and effective diffusion coefficient is recognized. However, a detailed local understanding of diffusion and sorption processes remains a challenge. As there is lack of proved models covering different length scales, existing classical concepts need to be evaluated with respect to their ability to reflect local geometries on the nanometer level. In this study, DSMC (Direct Simulation Monte Carlo) models were used to investigate the impact of pore microstructures on the diffusion behaviour of gases. It can be understood as a virtual pulse experiment within a single pore or a combination of different pore geometries.

Springer Handbook of Electrochemical Energy

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An Integrated Catalytic and Transient Study of Sulfated Zirconias: Investigation of the Reaction Mechanism and the Role of Acidic Sites in n‐Butane Isomerization

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Mechanical analysis of wafer testing with FEM simulations

The transient temporal analysis of products (TAP) pulse method has been applied to investigate the isomerization of n‐butane on sulfated zirconias at very low pressure. By combining these results with findings from XRD, XPS, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), temperature‐programmed desorption (TPD), and catalytic studies at atmospheric pressure, a wide range of pressure conditions can be accessed to study the influence of surface sulfate groups on the isomerization activity and the mechanism of this reaction. The catalytic activity of powder catalysts has been correlated to the surface site density of sulfates, with pyrosulfate structures playing a major role in the initiation of the reaction. The complex interplay between sulfate‐free and sulfate‐covered zirconia surfaces for the adsorption of alkanes has been investigated in detail, with TAP pulse experiments showing a monomolecular reaction pathway at low n‐butane partial pressures. Moreover, TAP pulse experiments have allowed detection of the reaction products of this initiation process, including butene and water, and have shown their influence on the deactivation of sulfated zirconias. Heats of adsorption have been calculated from the TAP pulse experiments.

Passive Cooling With Phase Change Material Energy Storage

Abstract In this work, finite element models are applied to analyze the influence of different parameters on crack failure probability during wafer testing. Regarding simulations, there are still very important aspects lacking in the existing literature. Very few publications take into account the plastic behavior of the metal layers of the structures. According to the results of this work, including plasticity in the simulations is essential to explain crack failure. Here we analyze how the applied force, mechanical properties and thickness of the layers are related to the deformation of the chip structure and the tensile stress in the oxide layer. Parametrizations are performed in order to find the main influences on crack failure. In a first approach, very simple models, which reproduce only pure elastic behavior, are considered. Subsequently, we present the results from more complex models, which reproduce the elastoplastic behavior of the metal layers. These simulation results are discussed and compared with experimental results from literature. Finally, conclusions and a prospective for future work are presented. A mesh and convergence analysis is included, in order to support the model results.

A New Approach to Determine Gas Diffusion Coefficients in Porous Solids by EIS: Application for NH3 and CO2 Adsorption on Zirconia and Zeolite Type 5A

A passive induced cooling system using phase change material (PCM) energy storage is presented in this analysis for providing indoor cooling and energy saving. Also, the latent heat performance of the PCM is analyzed. The supplied cooling capacity was evaluated using an indoor cooling temperature performance while the PCM characteristic performance was achieved by relating the applications sensible heat ratio efficiency to the charging and discharging effectiveness of the PCM. This is carried out for an office building in a warm humid climate. Obtained result delivered 24.54 % of the required indoor cooling load for 24°C indoor cooling temperature. Moreover, delivered indoor cooling capacity increased at constant increasing mean indoor temperature and PCM melting temperatures. Application sensible heat ratio efficiency was 77.66 % and average energy saving of 37.77 % in total energy operation cost was obtained. A CO2 emission reduction of 0.071 tons can also be achieved by the system.© 2013 ASME

Electrochemical Science — Historical Review

A new theoretical approach has been established to define transport coefficients of charge and mass transport in porous materials directly from impedance data; thus four transport coefficients could be determined. In case of ammonia adsorption on sulfated zirconia, the diffusion coefficient was figured out to be approximately the mobility diffusion coefficient of ammonium ions: 1.2 x 10-7 cm2/s. The transport of carbon dioxide was examined for samples of zeolite type 5A in different hydration states. By impedance spectroscopy measurements, the diffusion coefficient of water vapor at 373 K is estimated to be about 7 x 10-6 cm2/s. The influence of carbon dioxide adsorption on diffusion coefficients is studied based on two pellet types of zeolite 5A. The difference between polar and non-polar gas adsorption in porous solids is considered as changed characteristic of impedance.

Investigation of amorphous hydrogenated carbon layers as sacrificial structures for MEMS applications

Electrochemistry developed from the single contributions of famous researchers and scientists in the 150 years spanning 1776 and 1925. This increasing level of electrochemical knowledge over the 19th century dovetailed with the industrial revolution, turning the electrochemical discoveries of Galvani, Volta, Faraday, Coulomb, and Ohm into familiar principles, infusing their initial discoveries into every aspect of modern science – it is fair to say that no present-day scientist operates a computer or instrument without electrical current. Although modern electrochemists are no longer household names, electrochemistry has indisputably had bridging function in science and industrial applications and is at the basis of all modern sciences, from materials sciences and theoretical chemistry to biochemistry and medicine. A broad swath of electrochemical research still has a rich impact on the world, and the major scientific awards in electrochemistry are now awarded for work in biology/medicine and energy. Galvani would certainly be surprised at the follow on impact of his early studies of frog legs, and where those results leaped to over the last 220 years. This chapter surveys the history from its beginnings.