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- ItemIron-Based Binary Catalytic System for the Valorization of CO2 into Biobased Cyclic Carbonates(Washington, DC : ACS Publ., 2016) Büttner, Hendrik; Grimmer, Christoph; Steinbauer, Johannes; Werner, ThomasThe atom economic conversion of epoxidized vegetable oils and fatty acid derivatives with CO2 into cyclic carbonates permits the synthesis of novel oleo compounds from renewable resources as well as the valorization of CO2 as a C1-building block. Organic phosphorus salts proved to be selective catalysts for this reaction. In a widespread screening 11 inexpensive and nontoxic iron salts were evaluated as cocatalysts to enhance the reaction rate. In the presence of 0.25 mol % iron chloride the selectivity and conversion were significantly improved. The reaction parameters were optimized under solvent-free conditions, and the scope and limitation were evaluated for 9 epoxidized fatty acid esters and 4 epoxidized vegetable oils. The biobased carbonates were isolated in excellent yields up to 95% and can be considered to be based on 100% CO2 in respect to carbon. This binary catalyst system features high efficiency and plain simplicity while valorizing CO2 into cyclic carbonates based on renewable feedstocks.
- ItemInfluence of microwave plasma treatment on the surface properties of carbon fibers and their adhesion in a polypropylene matrix(London [u.a.] : Institute of Physics, 2016) Scheffler, C.; Wölfel, E.; Förster, T.; Poitzsch, C.; Kotte, L.; Mäder, G.; Madsen, Bo; Biel, A.; Kusano, Y.; Lilholt, H.; Mikkelsen, L.P.; Mishnaevsky Jr., L.; Sørensen, B.F.A commercially available carbon fiber (CF) with an epoxy-based sizing (EP-sized CF) and an unsized CF have been plasma treated to study the effect on the fiber-matrix adhesion towards a polypropylene matrix. The EP-sized fiber was chosen because of its predictable low adhesion in a polypropylene (PP) matrix. The fibers have been modified using a microwave low-pressure O2/CO2/N2-gas plasma source (Cyrannus®) developed at IWS in a batch process. One aim of this study was the evaluation of parameters using high energies and short time periods in the plasma chamber to see the effect on mechanical performance of CF. These results will be the fundamental work for a planned continuous plasma modification line. The CF surface was characterized by determining the surface energies, single fiber tensile strength and XPS analysis. The adhesion behavior before and after plasma treatment was studied by single fiber pull-out test (SFPO) and scanning electron microscopy (SEM). It was shown that the CO2- and O2-plasma increases the number of functional groups on the fiber surface during short time plasma treatment of 30 s. Carboxylic groups on the unsized CF surface resulting from O2-plasma treatment lead to an enhanced fiber-matrix adhesion, whereas the fiber strength was merely reduced.
- ItemPerpendicular magnetic anisotropy in the Heusler alloy Co2TiSi/GaAs(001) hybrid structure(New York : American Institute of Physics, 2015) Dau, M.T.; Jenichen, B.; Herfort, J.Investigation of the thickness dependence of the magnetic anisotropy in B2-type Co2TiSi films on GaAs(001), shows a pronounced perpendicular magnetic anisotropy at 10 K for thicknesses up to 13.5 nm. We have evidenced that the interfacial anisotropy induced by interface clusters has a strong influence on the perpendicular magnetic anisotropy of this hybrid structure, especially at temperatures lower than the blocking temperature of the clusters (28 K). However, as this influence can be ruled out at higher temperatures, the perpendicular magnetic anisotropy which is found to persist up to room-temperature can be ascribed to the magnetic properties of the Co2TiSi films. For thicknesses larger than 15.0 nm, we observe an alignment of the magnetic easy axis parallel to the sample surface, which is most likely due to the shape anisotropy and the film structure.
- ItemClimate change increases riverine carbon outgassing, while export to the ocean remains uncertain(München : European Geopyhsical Union, 2016) Langerwisch, F.; Walz, A.; Rammig, A.; Tietjen, B.; Thonicke, K.; Cramer, W.Any regular interaction of land and river during flooding affects carbon pools within the terrestrial system, riverine carbon and carbon exported from the system. In the Amazon basin carbon fluxes are considerably influenced by annual flooding, during which terrigenous organic material is imported to the river. The Amazon basin therefore represents an excellent example of a tightly coupled terrestrial–riverine system. The processes of generation, conversion and transport of organic carbon in such a coupled terrigenous–riverine system strongly interact and are climate-sensitive, yet their functioning is rarely considered in Earth system models and their response to climate change is still largely unknown. To quantify regional and global carbon budgets and climate change effects on carbon pools and carbon fluxes, it is important to account for the coupling between the land, the river, the ocean and the atmosphere. We developed the RIVerine Carbon Model (RivCM), which is directly coupled to the well-established dynamic vegetation and hydrology model LPJmL, in order to account for this large-scale coupling. We evaluate RivCM with observational data and show that some of the values are reproduced quite well by the model, while we see large deviations for other variables. This is mainly caused by some simplifications we assumed. Our evaluation shows that it is possible to reproduce large-scale carbon transport across a river system but that this involves large uncertainties. Acknowledging these uncertainties, we estimate the potential changes in riverine carbon by applying RivCM for climate forcing from five climate models and three CO2 emission scenarios (Special Report on Emissions Scenarios, SRES). We find that climate change causes a doubling of riverine organic carbon in the southern and western basin while reducing it by 20% in the eastern and northern parts. In contrast, the amount of riverine inorganic carbon shows a 2- to 3-fold increase in the entire basin, independent of the SRES scenario. The export of carbon to the atmosphere increases as well, with an average of about 30%. In contrast, changes in future export of organic carbon to the Atlantic Ocean depend on the SRES scenario and are projected to either decrease by about 8.9% (SRES A1B) or increase by about 9.1% (SRES A2). Such changes in the terrigenous–riverine system could have local and regional impacts on the carbon budget of the whole Amazon basin and parts of the Atlantic Ocean. Changes in riverine carbon could lead to a shift in the riverine nutrient supply and pH, while changes in the exported carbon to the ocean lead to changes in the supply of organic material that acts as a food source in the Atlantic. On larger scales the increased outgassing of CO2 could turn the Amazon basin from a sink of carbon to a considerable source. Therefore, we propose that the coupling of terrestrial and riverine carbon budgets should be included in subsequent analysis of the future regional carbon budget.
- ItemChanges in crop yields and their variability at different levels of global warming(München : European Geopyhsical Union, 2018) Ostberg, Sebastian; Schewe, Jacob; Childers, Katelin; Frieler, KatjaAn assessment of climate change impacts at different levels of global warming is crucial to inform the policy discussion about mitigation targets, as well as for the economic evaluation of climate change impacts. Integrated assessment models often use global mean temperature change (ΔGMT) as a sole measure of climate change and, therefore, need to describe impacts as a function of ΔGMT. There is already a well-established framework for the scalability of regional temperature and precipitation changes with ΔGMT. It is less clear to what extent more complex biological or physiological impacts such as crop yield changes can also be described in terms of ΔGMT, even though such impacts may often be more directly relevant for human livelihoods than changes in the physical climate. Here we show that crop yield projections can indeed be described in terms of ΔGMT to a large extent, allowing for a fast estimation of crop yield changes for emissions scenarios not originally covered by climate and crop model projections. We use an ensemble of global gridded crop model simulations for the four major staple crops to show that the scenario dependence is a minor component of the overall variance of projected yield changes at different levels of ΔGMT. In contrast, the variance is dominated by the spread across crop models. Varying CO2 concentrations are shown to explain only a minor component of crop yield variability at different levels of global warming. In addition, we find that the variability in crop yields is expected to increase with increasing warming in many world regions. We provide, for each crop model, geographical patterns of mean yield changes that allow for a simplified description of yield changes under arbitrary pathways of global mean temperature and CO2 changes, without the need for additional climate and crop model simulations.
- ItemCollateral transgression of planetary boundaries due to climate engineering by terrestrial carbon dioxide removal(München : European Geopyhsical Union, 2016) Heck, Vera; Donges, Jonathan F.; Lucht, WolfgangThe planetary boundaries framework provides guidelines for defining thresholds in environmental variables. Their transgression is likely to result in a shift in Earth system functioning away from the relatively stable Holocene state. As the climate system is approaching critical thresholds of atmospheric carbon, several climate engineering methods are discussed, aiming at a reduction of atmospheric carbon concentrations to control the Earth's energy balance. Terrestrial carbon dioxide removal (tCDR) via afforestation or bioenergy production with carbon capture and storage are part of most climate change mitigation scenarios that limit global warming to less than 2°C. We analyse the co-evolutionary interaction of societal interventions via tCDR and the natural dynamics of the Earth's carbon cycle. Applying a conceptual modelling framework, we analyse how the degree of anticipation of the climate problem and the intensity of tCDR efforts with the aim of staying within a "safe" level of global warming might influence the state of the Earth system with respect to other carbon-related planetary boundaries. Within the scope of our approach, we show that societal management of atmospheric carbon via tCDR can lead to a collateral transgression of the planetary boundary of land system change. Our analysis indicates that the opportunities to remain in a desirable region within carbon-related planetary boundaries only exist for a small range of anticipation levels and depend critically on the underlying emission pathway. While tCDR has the potential to ensure the Earth system's persistence within a carbon-safe operating space under low-emission pathways, it is unlikely to succeed in a business-as-usual scenario.
- ItemDeforestation in Amazonia impacts riverine carbon dynamics(München : European Geopyhsical Union, 2016) Langerwisch, Fanny; Walz, Ariane; Rammig, Anja; Tietjen, Britta; Thonicke, Kirsten; Cramer, WolfgangFluxes of organic and inorganic carbon within the Amazon basin are considerably controlled by annual flooding, which triggers the export of terrigenous organic material to the river and ultimately to the Atlantic Ocean. The amount of carbon imported to the river and the further conversion, transport and export of it depend on temperature, atmospheric CO2, terrestrial productivity and carbon storage, as well as discharge. Both terrestrial productivity and discharge are influenced by climate and land use change. The coupled LPJmL and RivCM model system (Langerwisch et al., 2016) has been applied to assess the combined impacts of climate and land use change on the Amazon riverine carbon dynamics. Vegetation dynamics (in LPJmL) as well as export and conversion of terrigenous carbon to and within the river (RivCM) are included. The model system has been applied for the years 1901 to 2099 under two deforestation scenarios and with climate forcing of three SRES emission scenarios, each for five climate models. We find that high deforestation (business-as-usual scenario) will strongly decrease (locally by up to 90%) riverine particulate and dissolved organic carbon amount until the end of the current century. At the same time, increase in discharge leaves net carbon transport during the first decades of the century roughly unchanged only if a sufficient area is still forested. After 2050 the amount of transported carbon will decrease drastically. In contrast to that, increased temperature and atmospheric CO2 concentration determine the amount of riverine inorganic carbon stored in the Amazon basin. Higher atmospheric CO2 concentrations increase riverine inorganic carbon amount by up to 20% (SRES A2). The changes in riverine carbon fluxes have direct effects on carbon export, either to the atmosphere via outgassing or to the Atlantic Ocean via discharge. The outgassed carbon will increase slightly in the Amazon basin, but can be regionally reduced by up to 60% due to deforestation. The discharge of organic carbon to the ocean will be reduced by about 40% under the most severe deforestation and climate change scenario. These changes would have local and regional consequences on the carbon balance and habitat characteristics in the Amazon basin itself as well as in the adjacent Atlantic Ocean.
- ItemDevelopment of Active and Stable Low Nickel Content Catalysts for Dry Reforming of Methane(Basel : MDPI, 2017-5-16) Ha, Quan Luu Manh; Armbruster, Udo; Atia, Hanan; Schneider, Matthias; Lund, Henrik; Agostini, Giovanni; Radnik, Jörg; Vuong, Huyen Thanh; Martin, AndreasMethane dry reforming (DRM) was investigated over highly active Ni catalysts with low metal content (2.5 wt %) supported on Mg-Al mixed oxide. The aim was to minimize carbon deposition and metal sites agglomeration on the working catalyst which are known to cause catalyst deactivation. The solids were characterized using N2 adsorption, X-ray diffraction, temperature-programmed reduction, X-ray photoelectron spectroscopy, and UV-Vis diffuse reflectance spectroscopy. The results showed that MgO-Al2O3 solid solution phases are obtained when calcining Mg-Al hydrotalcite precursor in the temperature range of 550–800 °C. Such phases contribute to the high activity of catalysts with low Ni content even at low temperature (500 °C). Modifying the catalyst preparation with citric acid significantly slows the coking rate and reduces the size of large octahedrally coordinated NiO-like domains, which may easily agglomerate on the surface during DRM. The most effective Ni catalyst shows a stable DRM course over 60 h at high weight hourly space velocity with very low coke deposition. This is a promising result for considering such catalyst systems for further development of an industrial DRM technology.
- ItemCharacterization of Bathyarchaeota genomes assembled from metagenomes of biofilms residing in mesophilic and thermophilic biogas reactors(London : BioMed Central Ltd., 2018) Maus, I.; Rumming, M.; Bergmann, I.; Heeg, K.; Pohl, M.; Nettmann, E.; Jaenicke, S.; Blom, J.; Pühler, A.; Schlüter, A.; Sczyrba, A.; Klocke, M.Background: Previous studies on the Miscellaneous Crenarchaeota Group, recently assigned to the novel archaeal phylum Bathyarchaeota, reported on the dominance of these Archaea within the anaerobic carbohydrate cycle performed by the deep marine biosphere. For the first time, members of this phylum were identified also in mesophilic and thermophilic biogas-forming biofilms and characterized in detail. Results: Metagenome shotgun libraries of biofilm microbiomes were sequenced using the Illumina MiSeq system. Taxonomic classification revealed that between 0.1 and 2% of all classified sequences were assigned to Bathyarchaeota. Individual metagenome assemblies followed by genome binning resulted in the reconstruction of five metagenome-assembled genomes (MAGs) of Bathyarchaeota. MAGs were estimated to be 65-92% complete, ranging in their genome sizes from 1.1 to 2.0 Mb. Phylogenetic classification based on core gene sets confirmed their placement within the phylum Bathyarchaeota clustering as a separate group diverging from most of the recently known Bathyarchaeota clusters. The genetic repertoire of these MAGs indicated an energy metabolism based on carbohydrate and amino acid fermentation featuring the potential for extracellular hydrolysis of cellulose, cellobiose as well as proteins. In addition, corresponding transporter systems were identified. Furthermore, genes encoding enzymes for the utilization of carbon monoxide and/or carbon dioxide via the Wood-Ljungdahl pathway were detected. Conclusions: For the members of Bathyarchaeota detected in the biofilm microbiomes, a hydrolytic lifestyle is proposed. This is the first study indicating that Bathyarchaeota members contribute presumably to hydrolysis and subsequent fermentation of organic substrates within biotechnological biogas production processes.
- ItemNiobium carbide nanofibers as a versatile precursor for high power supercapacitor and high energy battery electrodes(London [u.a.] : RSC, 2016) Tolosa, Aura; Krüner, Benjamin; Fleischmann, Simon; Jäckel, Nicolas; Zeiger, Marco; Aslan, Mesut; Grobelsek, Ingrid; Presser, VolkerThis study presents electrospun niobium carbide/carbon (NbC/C) hybrid nanofibers, with an average diameter of 69 ± 30 nm, as a facile precursor to derive either highly nanoporous niobium carbide-derived carbon (NbC–CDC) fibers for supercapacitor applications or niobium pentoxide/carbon (Nb2O5/C) hybrid fibers for battery-like energy storage. In all cases, the electrodes consist of binder-free and free-standing nanofiber mats that can be used without further conductive additives. Chlorine gas treatment conformally transforms NbC nanofiber mats into NbC–CDC fibers with a specific surface area of 1508 m2 g−1. These nanofibers show a maximum specific energy of 19.5 W h kg−1 at low power and 7.6 W h kg−1 at a high specific power of 30 kW kg−1 in an organic electrolyte. CO2 treatment transforms NbC into T-Nb2O5/C hybrid nanofiber mats that provide a maximum capacity of 156 mA h g−1. The presence of graphitic carbon in the hybrid nanofibers enabled high power handling, maintaining 50% of the initial energy storage capacity at a high rate of 10 A g−1 (64 C-rate). When benchmarked for an asymmetric full-cell, a maximum specific energy of 86 W h kg−1 was obtained. The high specific power for both systems, NbC–CDC and T-Nb2O5/C, resulted from the excellent charge propagation in the continuous nanofiber network and the high graphitization of the carbon structure.