Showing papers by "DECHEMA published in 2021"

A Unified Research Data Infrastructure for Catalysis Research – Challenges and Concepts

Abstract: Modern research methods produce large amounts of scientifically valuable data. Tools to process and analyze such data have advanced rapidly. Yet, access to large amounts of high‐quality data remains limited in many fields, including catalysis research. Implementing the concept of FAIR data (Findable, Accessible, Interoperable, Reusable) in the catalysis community would improve this situation dramatically. The German NFDI initiative (National Research Data Infrastructure) aims to create a unique research data infrastructure covering all scientific disciplines. One of the consortia, NFDI4Cat, proposes a concept that serves all aspects and fields of catalysis research. We present a perspective on the challenging path ahead. Starting out from the current state, research needs are identified. A vision for a integrating all research data along the catalysis value chain, from molecule to chemical process, is developed. Respective core development topics are discussed, including ontologies, metadata, required infrastructure, IP, and the embedding into research community. This Concept paper aims to inspire not only researchers in the catalysis field, but to spark similar efforts also in other disciplines and on an international level.

Intensification of Photobiocatalytic Decarboxylation of Fatty Acids for the Production of Biodiesel

Abstract: Light-driven biocatalytic processes are notoriously hampered by poor penetration of light into the turbid reaction media In this study, wirelessly powered light-emitting diodes are found to represent an efficient and scalable approach for process intensification of the photobiosynthetic production of diesel alkanes from renewable fatty acids

Thermochemistry and phase stability of the polymorphs of yttrium tantalate, YTaO4

Abstract: Thermodynamic parameters of the three fergusonite-related polymorphs M’, M and T of YTaO4 and their phase stabilities were investigated experimentally. The debate on the relative stability of the M and M’ phases was resolved, and it was shown that the compound does not transform to a cubic polymorph prior to melting. The enthalpies of formation of M and M’ were determined using high temperature oxide melt solution calorimetry, and the heat capacities and heat contents were measured. The enthalpy of the M’ to T phase transition was measured by differential thermal analysis. The stability of the T phase up to its melting at 2090 °C was demonstrated using high temperature X-ray diffraction and thermal analysis. Its enthalpy of fusion was determined using drop-and-catch calorimetry. The thermodynamic properties of YTaO4 assessed in this study enable the thermodynamic modeling of its polymorphs and related materials systems of technological importance.

Intensification of Heterogeneous Photocatalytic Reactions Without Efficiency Losses: The Importance of Surface Catalysis

Abstract: Advances in LED and photoreactor technology have brought semiconductor photocatalysis to the verge of feasibility of industrial application for the synthesis of value-added chemicals. However, the often observed efficiency losses under intensified illumination conditions still present a great challenge. This perspective discusses the origin of these efficiency losses and what needs to be done to prevent or counteract it and pave the way for efficient, intensified heterogeneous photocatalytic processes. The role of surface catalysis is particularly highlighted as one of the rate-limiting steps.

First time β-farnesene production by the versatile bacterium Cupriavidus necator.

Abstract: Terpenes are remarkably diverse natural structures, which can be formed via two different pathways leading to two common intermediates. Among those, sesquiterpenes represent a variety of industrially relevant products. One important industrially produced product is β-farnesene as a precursor for a jet fuel additive. So far, microbial terpene production has been mostly limited to known production hosts, which are only able to grow on heterotrophic substrates. In this paper, we for the first time describe β-farnesene production by the versatile bacterial host Cupriavidus necator on fructose, which is known to grow hetero- and autotrophically and even in bioelectrochemical systems. We were able to show a growth-dependent production of β-farnesene by expressing the β-farnesene synthase from Artemisia annua in C. necator H16 PHB-4. Additionally, we performed a scale-up in a parallel reactor system with production titers of 26.3 ± 1.3 µM β-farnesene with a fed-batch process. The β-farnesene production titers reported in this paper are not in the same range as titers published with known heterotrophic producers E. coli or S. cerevisiae. However, this proof-of-principle study with C. necator as production host opens new synthesis routes toward a sustainable economy and leaves room for further optimizations, which have been already performed with the known production strains.

Gram-scale production of the sesquiterpene α-humulene with Cupriavidus necator.

Abstract: Terpenoids have an impressive structural diversity and provide valuable substances for a variety of industrial applications. Among terpenes, the sesquiterpenes (C15 ) are the largest subclass with bioactivities ranging from aroma to health promotion. In this article, we show a gram-scale production of the sesquiterpene α-humulene in final aqueous concentrations of 2 g L-1 with the recombinant strain Cupriavidus necator pKR-hum in a fed-batch mode on fructose as carbon source and n-dodecane as an extracting organic phase for in situ product removal. Since C. necator is capable of both heterotrophic and autotrophic growth, we additionally modeled the theoretically possible yields of a heterotrophic versus an autotrophic process on CO2 in industrially relevant quantities. We compared the cost-effectiveness of both processes based on a production of 10 t α-humulene per year, with both processes performing equally with similar costs and gains. Furthermore, the expression and activity of 3-hydroxymethylglutaryl-CoA reductase (hmgR) from Myxococcus xanthus was identified as the main limitation of our constructed C. necator pKR-hum strain. Thus, we outlined possible solutions for further improvement of our production strain, for example, the replacement of the hmgR from M. xanthus by a plant-based variant to increase α-humulene production titers in the future.

Modeling and simulation-based design of electroenzymatic batch processes catalyzed by unspecific peroxygenase from A. aegerita.

Abstract: Unspecific peroxygenases have attracted interest due to their ability to catalyze the oxygenation of various types of C-H bonds using only hydrogen peroxide as a cosubstrate. Due to the instability of these enzymes at even low hydrogen peroxide concentrations, careful fed-batch addition of the cosubstrate or ideally in situ production is required. While various approaches for hydrogen peroxide addition have been qualitatively assessed, only limited kinetic data concerning enzyme inactivation and peroxide accumulation has been reported so far. To obtain quantitative insights into the kinetics of such a process, a detailed data set for a peroxygenase-catalyzed benzylic hydroxylation coupled with electrochemical hydrogen peroxide production is presented. Based on this data set, we set out to model such an electroenzymatic process. For this, initial velocity data for the benzylic hydroxylation is collected and an extended Ping-Pong-Bi-Bi type rate equation is established, which sufficiently describes the enzyme kinetic. Moreover, we propose an empirical inactivation term based on the collected data set. Finally, we show that the full model does not only describe the process with sufficient accuracy, but can also be used predictively to control hydrogen peroxide feeding rates To limit the concentration of this critical cosubstrate in the system.

Synthesis of mesoporous carbon spheres via a soft-template route for catalyst supports in PEMFC cathodes

Abstract: Synthesis of carbon spheres via a soft-template route should be further improved for industrial applications especially in terms of time, cost and scalability. The present work reports on the relatively fast production of mesoporous carbon via an ammonia-catalyzed hydrothermal soft-template one-pot route denoted as CFAH with m-aminophenol as the carbon source and triblock copolymer Pluronic® F127 as the template. For comparison, an acidic route with resol as the carbon precursor (CFRH) was evaluated as well. The best results regarding particle size and pore distribution of the as-prepared CFRH and CFAH samples were obtained in 2 M HCl and 6 M NH4OH at 120 °C for 12 h and 700 °C pyrolysis temperature, respectively. GDE with CFRH and CFAH supported platinum showed excellent ECSA retention of about 60–70% during accelerated degradation testing under half-cell conditions compared to only 13% for GDE with Pt/CVulcan reference material.

Critical assessment of the cyclic oxidation resistance of the aluminized Ti-48Al-2Cr-2Nb TiAl alloy at 700 °C and its impact on mechanical properties

Abstract: A comparative investigation of the oxidation resistance at 700 °C and the mechanical properties of the uncoated and pack aluminized Ti-48Al-2Cr-2Nb (in at. %) TiAl alloy was conducted in this study. Cyclic oxidation tests were performed for up to 1000 h in dry synthetic air. A mixed TiO2/Al2O3 scale formed on the surface of the uncoated TiAl alloy while a thin Al2O3-rich scale covered the surface of the aluminized samples. While stable α–Al2O3 together with rutile was detected on the surface of the uncoated samples, the oxide scale grown on coated samples consisted of α–Al2O3 and metastable θ–Al2O3. Four-point bending tests of the exposed samples at room temperature showed a progressive decrease in fracture stress and strain values of the uncoated alloy. The corresponding values of the aluminized samples were lower in the as-coated condition compared to the uncoated alloy, but then showed almost no further deterioration with increasing exposure.

Half-Cell State of Charge Monitoring for Determination of Crossover in VRFB-Considerations and Results Concerning Crossover Direction and Amount.

Abstract: Membranes play a crucial role in efficiency and longevity of flow batteries. Vanadium flow batteries suffer self-discharge and capacity fading due to crossover of electrolyte components through the membrane from one battery half-cell to the other. We consider the impact of vanadium species crossing ion exchange membranes on state of charge of the battery and we present a simple method to determine crossoverll open circuit potential measurements. State of s. State of charge for the negative and positive half-cell is simulated based on assumptions and simplifications for cation and anion exchange membranes and different crossover parameters. We introduce a crossover index "IndXovr" which enables the determination of crossover direction from state of charge data for the negative and positive half-cell and therewith identification of the half-cell in which predominant self-discharge occurs. Furthermore IndXovr allows statements on crossover amount in dependence on state of operation. Simulated case studies are compared to experimental state of charge values estimated from half-cell potential measurements. Our results reveal that half-cell potential monitoring respectively half-cell SOC estimation, is a simple and suitable tool for the identification of crossover direction and relative amount of crossover in VFB.

Volatile fatty acid platform - a cornerstone for the circular bioeconomy.

Abstract: Annually, the EU produces more than 100 million tonnes of urban biowaste, which is largely under-valorized and in some cases even still landfilled without any energy or material recovery. If Europe wants to be ready for the future, it will need to make better use of this large biomass potential within a circular economy approach. The research project funded by the European Commission under the Horizon 2020 programme entitled 'VOLATILE-Biowaste derived volatile fatty acid platform for biopolymers, bioactive compounds and chemical building blocks' aimed to produce volatile fatty acids (VFAs) from biowaste for reprocessing into products, materials or substances to close the material loop. During the project, the partners were able to obtain average volatile fatty acid yields of 627 g COD/kg organic matter (OM) for food waste, 448 g COD/kg OM for separately collected vegetable, garden and fruit waste (VGF) and 384 g COD/kg OM for the organic fraction of municipal solid waste (OF-MSW) at concentrations ranging from 12 to 48 g/L, 6 to 40 g/L and 13 to 26 g/L, respectively. A membrane filtration cascade consisting of micro-, ultra- and nano-filtration followed by reverse osmosis was identified as a feasible way to purify and concentrate the VFA effluent, making them a suitable carbon source for further fermentation processes. Besides technical optimization, socio-economic and legal aspects associated with this platform technology were also studied and show that although this technology is still in development, it is providing an answer to changing societal and market expectations both regarding organic waste treatment and bio-based production strategies. Based on the current technological, economic and market evolutions, it is expected that the VFAP will play an important role in organic waste treatment in the coming years.

Microstructure and area specific resistance of cathodic half cells for solid oxide fuel cells composed of perovskite-type cathodes and Co-alloy-coated ferritic stainless steel interconnects

Abstract: In order to prevent oxidation and Cr poisoning, a Co-W coating has been applied on ferritic stainless steel (FSS), which is used as the interconnect parts of solid oxide fuel cells (SOFCs). However, the electrical properties of the Co–W-coated stainless steels have not yet been evaluated. In this study, cathodic half-cells were experimentally manufactured with La0.8Sr0.2MnO3 (LSM) and La0.8Sr0.2Co0.8Fe0.2O3 (LSCF) as cathodes, and uncoated, Co-coated, and Co–W-coated FSSs as interconnects, respectively. Then their oxidation property and area-specific resistance (ASR) were evaluated at 800 °C. Based on phase identification and microstructural analysis, the Co–W-coating was confirmed to effectively suppress the Cr poisoning of the cathode. The ASR values of the Co–W-coated steel with LSM and LSCF as cathodes were 102 and 97 mΩ cm2, respectively, which are adequate for SOFC application. Furthermore, when the LSM was applied as a cathode material, the formation of Mn spinels enhanced the adherence between the cathode and interconnected parts. Thus, the combination of Co–W-coated FSS steel with LSM as the cathode material exhibited the optimal combination of electrical conductivity and microstructural stability. Graphic abstract.

Mechanical Stability Diagrams for Thermal Barrier Coating Systems

Abstract: Loss of mechanical integrity due to thermal aging and subsequent spallation of the ceramic top layer is one of the dominant failure mechanisms in thermal barrier coating systems. In order to predict and avoid such mechanical failure, a strain-based lifetime assessment model is presented for a novel double-layer thermal barrier system. The investigated ceramic system consists of a gadolinium zirconate layer on top of a layer of yttria-stabilized zirconia prepared by atmospheric plasma spraying. The mechanical stability diagrams generated by the model delineate areas of safe operation from areas where mechanical damage of the thermal barrier coating becomes imminent. Intensive ceramographic inspection is used to investigate the defect growth kinetics in the ceramic top coat after isothermal exposure. Four-point bending experiments with in situ acoustic emission measurement are utilized to determine the critical strain to failure. The results are then used to generate mechanical stability diagrams for the thermal barrier coatings. From these diagrams, it becomes evident that the gadolinium zirconate layer has significantly lower strain tolerance than the yttria-stabilized zirconia. However, the underlying yttria-stabilized zirconia layer will provide some thermal protection even when the gadolinium zirconate layer has failed.

Application of the pack cementation process on SiC/SiC ceramic matrix composites

Abstract: The potentials and limitations of a halide-activated pack cementation process on SiC/SiC Ceramic Matrix Composites for the development of bond coats as part of environmental barrier coating (EBCs) systems were investigated. Different pack compositions using chromium, aluminum and alloys of these elements were tested and the kinetics of coating formation were examined in addition to their microstructure. The results and their analogy to diffusion couples were discussed and it was shown that coating elements which form silicides and carbides are promising candidates for coatings deposited on SiC/SiC via pack cementation. Based on such considerations a two-step pack cementation was proposed, which used chromium, one of the suitable elements, in a first step, to finally achieve an alumina-forming coating. The oxidation resistance of the developed coating was tested via thermogravimetric analysis and compared to the uncoated material. The coating protected the fiber-matrix interface of the SiC/SiC Ceramic Matrix Composites from oxidation.

The Influence of Oxide Color on the Surface Characteristics of Zirconium Alloy ZrNb₇ (wt%) After Different Heat Treatments

Abstract: Oxidized zirconium alloys can appear as black, white and all gray shades depending on the heat treatment process. The black color results from a high amount of oxygen vacancies in non-stoichiometric zirconia (ZrO2−x) that effectively reduces the band gap of the material. In this work we compare the surface properties of black and white zirconia on ZrNb7 substrate. An oxidation in air at 600 °C for 1 h results in a dark-gray oxide with only a few micro cracks. Oxidation at low oxygen partial pressure at 600 °C for 8 h (pO2 = 10–19 Pa) generates a dense, totally black oxide scale. A three step heat treatment process, that was introduced for better coating adhesion, results in a white oxide layer with many micro cracks parallel to the surface. From the results of various microscopy and spectroscopy techniques, we derive a model of the layer formation of zirconia on ZrNb7 and give reason why black zirconia, and therefore the oxidation at low oxygen partial pressure, is favorable for tribological applications (e.g., artificial joint replacements).

Infrastructure Challenges Caused by Industrial Transformation to Achieve Greenhouse Gas Neutrality. Ammonia Production in the Antwerp‐Rotterdam‐Rhine‐Ruhr Area

Abstract: Several pathways for potentially greenhouse gas neutral production of ammonia have been investigated compared to today's conventional ammonia production at chemical sites in Antwerp, Dormagen, and Geleen. These pathways include on-site water electrolysis using grid electricity, off-site production via water electrolysis using renewable electricity and supply of green hydrogen to the site, pyrolysis of natural gas and conventional ammonia production coupled with CO2-capture on-site and transport to a storage site. All pathways effectively eliminate scope 1 emissions present in conventional production but continue to emit scope 2 emissions from grid electricity consumption. Eventually, a coordinated industry-wide and cross-industry effort is needed to address the transformational changes and develop the common cross-border infrastructures.

Structural, Magnetic and Catalytic Properties of a New Vacancy Ordered Perovskite Type Barium Cobaltate BaCoO2.67.

Abstract: A new vacancy ordered, anion deficient perovskite modification with composition of BaCoO2.67 (Ba3 Co3 O8 □1 ) has been prepared via a two-step heating process. Combined Rietveld analysis of neutron and X-ray powder diffraction data shows a novel ordering of oxygen vacancies not known before for barium cobaltates. A combination of neutron powder diffraction, magnetic measurements, and density functional theory (DFT) studies confirms G-type antiferromagnetic ordering. From impedance measurements, the electronic conductivity of the order of 10-4 S cm-1 is determined. Remarkably, the bifunctional catalytic activity for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is found to be comparable to that of Ba0.5 Sr0.5 Co0.8 Fe0.2 O3-y , confirming that charge-ordered anion deficient non-cubic perovskites can be highly efficient catalysts.

Influence of Water Vapor and Temperature on the Oxide Scale Growth and Alpha-Case Formation in Ti-6Al-4V Alloy

Abstract: The Ti-6Al-4V alloy is extensively used in aerospace, automotive and biomaterial applications. In the aerospace industry, the service temperature of Ti-6Al-4V is currently limited to 350 °C due to its insufficient oxidation resistance. Oxidation at higher temperatures causes the formation of a fast-growing oxide scale and an oxygen-enriched subsurface layer, which is known as the “alpha-case.” Additionally, the effect of water vapor on the oxidation behavior is critical. In the present study, the oxidation behavior of Ti-6Al-4V in dry air and air containing 10 vol.% H2O at 500, 600 and 700 °C for up to 500 h has been investigated. The main focus of this study is the examination of the different oxide scale morphologies along with the oxygen enrichment in the subsurface zone. It has been observed that spallation of the oxide scale is more severe in a water vapor-containing environment. In dry air, the oxide morphology shows the typical layered TiO2/Al2O3 structure after exposure at 700 °C for 300 h, while Al2O3 precipitates are present in the outermost part of the TiO2 scale when oxidized in wet air. This indicates that the solubility and diffusivity of Al3+ ions in TiO2 are influenced by water vapor. In addition, the extent of oxygen enrichment in the subsurface zone (alpha-case) as a function of temperature and time is determined by nanoindentation profiles. It was shown that in contrast to the scale formation, the alpha-case thickness is not affected by the presence of water vapor in the atmosphere.

Self-Compensation of Cross Influences using Spectral Transmission Ratios for Optical Fiber Sensors in Lithium-Ion Batteries

Abstract: In this paper, we discuss some major obstacles and solutions towards an industrialization of optical fiber sensors for cell state monitoring of lithium-ion batteries. We present measurement results based on transmitted light intensities through the optical fiber as indicator for the state of charge. Cells are built with commercial electrodes in a pouch cell setup. To compensate for cross influences and stabilize the measuring signal against manufacturing tolerances, a referencing method is introduced. Thus, ratios of transmitted light intensities at different wavelengths are evaluated to avoid the use of absolute values. The obtained transmission ratios are in good agreement with the state of charge for various C-rates. Finally, possibilities towards an industrial implementation with inexpensive LEDs and phototransistors are discussed.

Discontinuities in Oxidation Kinetics: A New Model and its Application to Cr–Si-Base Alloys

Abstract: Some alloys such as many Cr-based systems show mass gain discontinuities during thermogravimetric measurements which strongly affect the oxidation kinetics. The behaviour cannot be described by the current models available in the literature. Thus, a novel $$k_\mathrm{para}$$ – $$k_\mathrm{lin}$$ -P-model was developed to describe oxidation kinetics during the isothermal exposure of materials which show such behaviour. Beside the parabolic rate constant $$k_\mathrm{para}$$ and the linear mass loss constant $$k_\mathrm{lin}$$ , the P-value and $$f_P$$ are introduced to take into account spontaneous rapid mass gains due to local oxide scale failure. The parameter P serves as a measure for the mass gain due to discontinuous events and $$f_P$$ is the frequency of such events. The both parameters can be related to oxide scale detachment and growth stresses. The application of the model is demonstrated for the oxidation of Cr–Si-based alloys in synthetic air at $$1200^{\circ }\hbox {C}$$ for 100 h. For these alloys, the origin of the mass gain discontinuities is discussed and the meaning of P and $$f_P$$ is explained in more detail. Using this newly developed model, an insight into growth and nitridation resistance of oxide scales as well as scale adhesion is gained.

Conductive Geopolymers as Low-Cost Electrode Materials for Microbial Fuel Cells.

Abstract: Geopolymer (GP) inorganic binders have a superior acid resistance compared to conventional cement (e.g., Portland cement, PC) binders, have better microbial compatibility, and are suitable for introducing electrically conductive additives to improve electron and ion transfer properties. In this study, GP-graphite (GPG) composites and PC-graphite (PCG) composites with a graphite content of 1-10 vol % were prepared and characterized. The electrical conductivity percolation threshold of the GPG and PCG composites was around 7 and 8 vol %, respectively. GPG and PCG composites with a graphite content of 8 to 10 vol % were selected as anode electrodes for the electrochemical analysis in two-chamber polarized microbial fuel cells (MFCs). Graphite electrodes were used as the positive control reference material. Geobacter sulfurreducens was used as a biofilm-forming and electroactive model organism for MFC experiments. Compared to the conventional graphite anodes, the anode-respiring biofilms resulted in equal current production on GPG composite anodes, whereas the PCG composites showed a very poor performance. The largest mean value of the measured current densities of a GPG composite used as anodes in MFCs was 380.4 μA cm-2 with a standard deviation of 129.5 μA cm-2. Overall, the best results were obtained with electrodes having a relatively low Ohmic resistance, that is, GPG composites and graphite. The very first approach employing sustainable GPs as a low-cost electrode binder material in an MFC showed promising results with the potential to greatly reduce the production costs of MFCs, which would also increase the feasibility of MFC large-scale applications.

Influence of Process Parameters on the Tribological Behavior of PEO Coatings on CP-Titanium 4+ Alloys for Biomedical Applications.

Abstract: Wear resistant ceramic coatings were generated on novel commercially pure titanium grade 4+ alloys by the plasma electrolytic oxidation technique (PEO) in an aluminate and zirconia containing electrolyte. The coatings were obtained adopting a full regular two-level factorial design of experiments (DoE) varying the PEO process parameters current density, repetition rate and duty cycle. The generated coatings were characterized with respect to its wear resistance and mechanical properties by reciprocal ball-on-flat tests and nanoindentation measurements. Thickness, morphology and phase formation of the PEO coatings was analyzed by scanning electron microscopy (SEM/EDS) and X-ray diffraction. XRD results indicate the formation of crystalline aluminium titanate (TiAl2O5) as well as t-ZrO2 and alumina leading to an increase in hardness and wear resistance of the PEO coatings. Evaluation of the DoE's parameter interaction shows that the main effects for generating wear resistant coatings are current density and repetition rate. In particular, the formation of mechanically stable and adhesive corundum and zirconia containing coatings with increasing current density and frequency turned out to be responsible for the improvement of the tribological properties. Overall, the PEO processing significantly improves the wear resistance of the CP titanium base alloy.