DECHEMA

About: DECHEMA is a nonprofit organization based out in Frankfurt am Main, Germany. It is known for research contribution in the topics: Corrosion & Oxide. The organization has 756 authors who have published 1307 publications receiving 25693 citations.

Application of gas diffusion electrodes in bioelectrochemical syntheses and energy conversion

Abstract: Combining the advantages of biological components (e.g., reaction specificity, self-replication) and electrochemical techniques in bioelectrochemical systems offers the opportunity to develop novel efficient and sustainable processes for the production of a number of valuable products. The choice of electrode material has a great impact on the performance of bioelectrochemical systems. In addition to the redox process at the electrodes, interactions of biocatalysts with electrodes (e.g., enzyme denaturation or biofouling) need to be considered. In recent years, gas diffusion electrodes (GDEs) have proved to be very attractive electrodes for bioelectrochemical purposes. GDEs are porous electrodes, that posses a large three-phase boundary surface. At this interface, a solid catalyst supports the electrochemical reaction between gaseous and liquid phase. This mini-review discusses the application of GDEs in microbial and enzymatic fuel cells, for microbial electrolysis, in biosensors and for electroenzymatic synthesis reactions.

Isothermal oxidation of α2-Ti3Al

Abstract: The isothermal oxidation behavior of binary Ti–25 at.% Al was studiedat 1073, 1173, and 1273 K in air and oxygen with emphasis on themicrostructure of the subsurface zone underneath the external oxidescale. Thermogravimetric analysis, acoustic-emission (AE) analysis, lightmicroscopy, scanning electron microscopy (SEM), atomic force microscopy(AFM), and cross-sectional transmission electron microscopy (TEM) werecarried out. Three layers could be identified in the subsurface regionconsisting of an internal oxidation zone of α-Al2O3,and α-Ti, a ternary phase with the empirical formulaTi–21Al–15O (at.%), and an oxygen penetration zone consisting ofα2-Ti3Al(O).

Ferritic–martensitic steels: Improvement of the oxidation behavior in steam environments via diffusion coatings

Abstract: New generation heat-resistant ferritic–martensitic steels are of great interest as superheater materials in fossil fuel power plants. The oxidation resistance of these chromium steels (9 wt.%) in water vapor containing environments above 600 °C still requires improvement. One major problem is the breakdown of the chromia layer by formation of volatile chromium species CrO2(OH)2 promoted by water vapor in the atmosphere. Both, the fire-side as well as the steam side of the superheater tube can be affected due to high contents of water vapor in these atmospheres. With the goal to operate ferritic–martensitic steels under such conditions, enrichment of the substrate with chromium and manganese was carried out using three different pack cementation processes: pure chromium coating, 2-step chromium and manganese process and simultaneous deposition of chromium and manganese. All three surface-treated alloys show exceptional stabilities in steam environments, as illustrated by oxidation exposures in argon/50% water vapor at 650 °C for 3000 h. The pure chromium coating on the P91 substrate revealed the best oxidation behavior in steam.

Selektive C-H-Bindungsaktivierung durch eine Kaskade aus Photochemie und Biokatalyse

Abstract: Selektive Oxyfunktionalisierungen von inerten C-H-Bindungen konnen unter milden Bedingungen durch den Einsatz von Peroxygenasen erreicht werden. Dieser Ansatz wird jedoch durch die schlechte Stabilitat der Enzyme in Anwesenheit stochiometrischer Mengen des Oxidationsmittels Wasserstoffperoxid erschwert. Hier zeigen wir, dass sich anorganische Photokatalysatoren wie goldbeladenes Titandioxid zur effizienten Bereitstellung geeigneter Mengen an H2O2 durch reduktive Aktivierung von Umgebungssauerstoff und simultaner Oxidation von Methanol eignen und gleichzeitig eine hohe Reaktivitat und Stabilitat des Enzyms gewahrleisten. Mithilfe dieses Ansatzes konnte die stereoselektive Hydroxylierung von Ethylbenzol zu (R)-1-Phenylethanol in hoher Enantioselektivitat (>98 % ee) und sehr hoher katalytischer Produktivitat (TON>71.000) erreicht werden.

Analysis of the coupled transport, reaction, and deactivation phenomena in the immobilized glucose oxidase and catalase system.

Abstract: In a previous paper, the overall or macrokinetics of the immobilized glucose oxidase--catalase system has been presented. In this paper a detailed analysis of the interaction of diffusion and reaction in this system will be presented. The mathematical treatment includes two consecutive reactions with two-substrate kinetics. Furthermore, the deactivation of both enzymes due to the intermediate product peroxide is taken into account. The predicted results suggest that the efficiency of the glucose oxidase reaction depends on the concentration ranges of the two substrates. Furthermore, the external mass-transfer rate may cause a shift from glucose limitation to oxygen limitation. The efficiency of the coupled system is always higher than that predicted for the uncoupled reaction path. The calculations show that the economics of the coupled system depend a great deal on the deactivation of the enzymes.