Cathodic scattering catalysts

It has been shown that enantioselectivity is increased at low conversions particularly with the catalysts using cathodic scattering of metals (0.4-0.8 atomic layers on the surface of quartz). The temperature dependence of asymmetric decomposition of butan-2-ol revealed two maxima of optical rotation of products at temperatures between 320 - 400° butan-2-ol mainly dehydrogenates and at higher temperatures, above 400°, dehydration takes place. Therefore, in the reaction on Cu-<7-quartz catalysts two maxima of optical rotation were found at 340°C a = 0.21° and at 530°C a = 0.25°... 

It was found that Cu-c/-quartz catalysts are more effective than the others in the asymmetric decomposition of 2-butanol and that the sign of optical rotation of the product after the dehydrogenation reaction always corresponded to the sign of rotation of the quartz. Ag-quartz catalysts prepared by cathodic scattering contained 0.03-0.08% Ag and gave an an of +0.106° on Ag-r/-quartz and -0.07° on Ag-/-quartz at the optimal temperature of 370°C. Two maximal values of optical rotation were observed on Ni-quartz catalysts, too -0.012° on Ni-/-quartz and +0.16° on Ni-r/-quartz. 

The elemental composition, oxidation state, and coordination environment of species on surfaces can be determined by X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) techniques. Both techniques have a penetration depth of 5-20 atomic layers. Especially XPS is commonly used in characterization of electrocatalysts. One common example is the identification and quantification of surface functional groups such as nitrogen species found on carbon-based catalysts.26-29 Secondary Ion Mass spectrometry (SIMS) and Ion Scattering Spectroscopy are alternatives which are more surface sensitive. They can provide information about the surface composition as well as the chemical bonding information from molecular clusters and have been used in characterization of cathode electrodes.30,31 They can also be used for depth profiling purposes. The quantification of the information, however, is rather difficult.32... 

Synchotron based techniques, such as surface X-ray scattering (SXS) and X-ray absorption spectroscopy (XAS), have found increased use in characterization of electrocatalysts during electrochemical reactions.37 These techniques, which can be used for characterization of surface structures, require intricate cell designs that can provide realistic electrochemical conditions while acquiring spectra. Several examples of the use of XAS and EXAFS in non-precious metal cathode catalysts can be found in the literature.38 2... 

Platinum-Based Cathode Catalysts for Polymer Electrolyte Fuel Cells, Fig. 4 (a) Auger electron spectroscopy of as-sputtered and annealed PtaNi. (b) Low-energy ion-scattering spectra of the same two surfaces,... 

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