Schubert, Miriam
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Schubert, Miriam
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Schubert, Miriam
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Item-typ:Veröffentlichung, The Influence of the Pyrolysis Temperature on the Material Properties of Cobalt and Nickel Containing Precursor Derived Ceramics and their Catalytic Use for CO2 Methanation and Fischer–Tropsch Synthesis(2016-11-25); ; ; ; Ni and Co containing precursor derived ceramics (ceramers) were prepared from a polysiloxane based preparation route. All catalysts were characterised by BET, XRD and TEM as well as by water and heptane adsorption and tested for CO2 methanation and Fischer–Tropsch synthesis. Different pyrolysis temperatures between 400 and 600 °C were used to get catalysts with different surface hydrophilicities. With increasing synthesis temperature less organic groups remain on the surface, resulting in a more hydrophilic catalyst. For all Ni containing ceramers, well dispersed particles in the range of 3 nm were formed and comparable surface areas were found. The catalysts with the lowest tendency towards water adsorption showed the highest activity for CO2 methanation. In contrast to the Ni catalysts, for the Co containing ceramers particle formation was dependent on the pyrolysis temperature. While no metallic particles were formed at 400 °C, small particles in the range of ~5 nm were obtained, using a pyrolysis temperature of 500 °C. Increasing the pyrolysis temperature to 600 °C, the particle size increased to ~10 nm. First tests for CO2 methanation and Fischer–Tropsch reaction were successfully carried out and the catalysts with the less hydrophilic surface showed higher activity and a higher selectivity towards C5+-products.Wissenschaftlicher Artikel312 552 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, In situ analysis of gas phase reaction processes within monolithic catalyst supports by applying NMR imaging methods(Elsevier, 2016-06-07); ; ; ; Measuring spatially resolved concentration distributions in gas phase reaction systems is an important tool to validate simulation calculations, improve the understanding of transport processes within the catalyst, and identify potentials for improvements of monolithic catalyst supports. The commonly used measurement methods for such opaque systems are invasive and, thus, might be misleading due to alteration of the system. To overcome this issue, a 3D magnetic resonance spectroscopic imaging (MRSI) method was developed and implemented on a 7-Tesla NMR imaging system to map the concentration distributions within opaque monolithic catalysts using the ethylene hydrogenation process as case study. The reaction was catalyzed by a coated sponge packing or a honeycomb monolith within an NMR compatible packed bed reactor. Temperatures at the inlet and the outlet of the catalyst beds were simultaneously determined by analyzing the spectra of inserted ethylene glycol filled glass capsules. Steady state concentration profiles and temperature levels were measured at different reaction conditions. In order to prove the plausibility of the measured spatial distributions of compound concentrations, the experimental results were compared to a 1D model of the reactor based on kinetic data from literature. Furthermore, a comparison with integral concentration measurements using a mass spectrometer demonstrated deviations below 5%. The results show that 3D MRSI is a valuable and reliable tool to non-invasively measure spatially resolved process parameters within optically and/or mechanically inaccessible structured monolithic catalyst supports, even if only standard thermal polarization is exploited and the use of expensive and technically challenging signal enhancement techniques (hyperpolarization) is avoided. We expect that 3D MRSI can pave the way toward deeper insight into the interactions between catalyst, catalyst support, and gas phase.Wissenschaftlicher ArtikelBand:273117 131 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Coatings of active and heat-resistant cobalt-aluminium xerogel catalysts(Elsevier, 2016-05-28); ; ; ; The application of catalytically coated metallic foams in catalytic processes has a high potential for exothermic catalytic reactions such as CO2 methanation or Fischer-Tropsch synthesis due to good heat conductivity, improved turbulent flow properties and high catalyst efficiencies. But the preparation of homogenous catalyst coats without pore blocking is challenging with conventional wash coating techniques. Here, we report on a stable and additive free colloidal CoAlOOH suspension (sol) for the preparation of catalytically active Co/Al2O3 xerogel catalysts and coatings. Powders with 18wt% Co3O4 prepared from this additive free synthesis route show a catalytic activity in Fischer-Tropsch synthesis and CO2 methanation which is similar to a catalyst prepared by incipient wetness impregnation (IWI) after activating the material under flowing hydrogen at 430°C. Yet, the xerogel catalyst exhibits a much higher thermal stability as compared to the IWI catalyst, as demonstrated in catalytic tests after different heat agings between 430°C and 580°C. It was also found that the addition of polyethylene glycol (PEG) to the sol influences the catalytic properties of the formed xerogels negatively. Only non-reducible cobalt spinels were formed from a CoAlOOH sol with 20wt% PEG. Metallic foams with pores sizes between 450 and 1200μm were coated with the additive free CoAlOOH sol, which resulted in homogenous xerogel layers. First catalytic tests of the coated metal foams (1200μm) showed good performance in CO2 methanation.Wissenschaftlicher ArtikelBand:47783 116