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A liquid core waveguide membrane microreactor is a novel concept that allows in situ spectroscopy to be carried out in an optical microreactor, while enabling a very high gas-to-liquid mass transfer. The potential of this reactor concept to derive kinetics in gas/liquid reactions is demonstrated using the heteropoly acids catalyzed oxidation of biomass to formic acid (the ‘OxFA process’). For vanadium-substituted, Keggin-type heteropoly acids, the kinetics of the reduction and reoxidation step of the catalyst cycle was deduced using in situ UV/Vis spectroscopy. Reduction was studied from 40 to 80 °C: a strong dependency of the reduction kinetics was deduced. In combination with additional cyclic voltammetry and EPR characterization, it can be assumed that two active centers promote this reaction, while the existence and proportions of both types depends on the degree of vanadium substitution. The rapid mass transfer allowed transient response experiments to be carried out for the reoxidation step, which was studied up to 150 °C. Switching from anaerobic to aerobic conditions, an even stronger dependency of the reoxidation kinetics on the degree of vanadium substitution was revealed.

Oxidation of acrolein to acrylic acid on a Mo/V/W mixed oxide catalyst was studied by transient (cyclic temperature-programmed (TP)) as well as steady-state methods. TP reactions (TPReactions) exhibit an activity hysteresis of the catalyst with respect to temperature. As a result of the steady-state measurements, the activity hysteresis is not related to multiple steady states and is exclusively a transient phenomenon. Generally, the dynamics of bulk oxygen plays a key role leading to a reversible oxidation/reduction of the catalyst surface which influences the activity. This means the bulk acts as oxygen buffer. In this context, a reaction model, which involves the participation of bulk oxygen, was deduced and verified by modeling.

Interest in energy storage technologies is still increasing in times of the excess of electricity that is generated by wind farms or solar plants. Solar electricity can be transformed to solar-hydrogen via water electrolysis. A crucial part of the energy storage technologies plays the efficient conversion of H2 and CO2 from renewable resources. Here, the process conditions for continuously catalytic hydrogenation of CO2 to CH3OH under supercritical conditions over lab-synthesized Cu/ZnO/Al2O3 catalysts were investigated. The impact of temperature (230 – 330 °C), residence time (0.5 - 2.2 s) at moderate pressure (150 bar) but even above the supercritical parameters of CO2 showed a selective CO2 hydrogenation. Higher H2 concentrations, respectively higher H2:CO2-ratios (H2:CO2 = 6), lead to an increased selectivity of CH3OH. A possible in situ phase separation of reaction products within the reactor due to the higher densities of the reaction mixture by the highered pressure could affect the kinectics and simplfy the down-stream processing. The combination of thermodynamic studies (phase separation phenomena) as well as the catalytic performance tests for the CO2 hydrogenation under supercritical conditions are discussed. Based on these data a process concept is presented.

Zur besseren Nutzung von Exzessenergien wurde ein Warmespeichersystem entwickelt, das sich aus einem Blockheizkraftwerk (BHKW) mit einem integrierten Langzeitwarmespeicher zusammensetzt. Aus okonomischen Grunden wird ein BHKW ganzjahrig bei optimalem Wirkungsgrad betrieben. Die Folge ist, dass Warmeenergie im Sommer sinnvollerweise gespeichert werden sollte, um sie in der Heizperiode zu nutzen. Hierbei wird als Warmespeichersystem ein binares System bestehend aus einem modifizierten Zeolith 5A und Ammoniak eingesetzt. Die abschliesende Auslegung zeigt, dass es als Kurz- und Langzeitwarmespeicher eingesetzt werden kann.

During the acrylic acid (AA) storage a quality loss occurs due to the formation of by-products such as diacrylic acid (DiAA), triacrylic acid (TriAA) and higher oligomers. This problem intensifies in the presence of water since the formation rate of oligomers increases and further byproducts such as 3hydroxypropionic acid (3-HPA) and 3hydroxydiacryl acid (3-HDiAA) are formed. However, water is often essential during storage and transport to rise the flashpoint or to reduce the melting point. In the literature only the formation of DiAA has been investigated. In this work the formation kinetics are investigated for all mentioned components at 100 °C in pure and aqueous AA containing 5, 10 and 20 wt% water. The formation mechanisms of 3-HPA and 3-HDiAA are assumed as acid catalyzed ester hydrolyses of DiAA or TriAA. The hydration of AA to 3-HPA is excluded because the formation process does not exhibit a second order kinetic reaction. The introduced reactions are modelled with the measured kinetic data in order to confirm the proposed reactions.

To diversify energy sources and to address the impacts of global warming, the transformation of biomass, a renewable energy source, into fuels and chemicals is becoming increasingly necessary. The gasification technology is an efficient way of converting biomass via syngas into sustainable fuels. By-products, especially tar, are formed during the gasification process and need to be removed before further downstream processing. Mo/V/W-mixed oxides were found to be applicable for the catalytic tar oxidation in CO/H2 atmosphere by adding a stoichiometric amount of oxygen. In temperature-programmed experiments the reactivity of different tar model compounds during the selective oxidation on Mo/V/W-mixed oxides as well as the catalytic performances of V2O5, WO3, and MoO3 during the tar oxidation were investigated.

In today’s vehicle applications, SCR ammonia dosing is completed using complex control algorithms that need to be parameterized for the individual catalyst technology. Owing to the complexity of the parameterization procedures, ammonia dosing is frequently completed using either oversimplified dosing strategies (e.g., constant NH 3 /NO x ratio) or strategies previously optimized for different catalysts during the early design phase’s simulation and laboratory studies. This paper presents a practical, model-based approach that allows for simulation and laboratory studies to be performed with an individually adapted dosing profile. The procedure is based on conventional feedback control strategies, where the average ammonia storage level is controlled using a temperature dependent setpoint (the desired storage level), which is interpolated from a look-up table. The approach of this paper is to optimize numerically the entries of this look-up table for a given test cycle such that the NO x conversion is maximized while the ammonia slip is kept below a defined level. Although the optimization is performed for a particular cycle, it is demonstrated that the dosing strategies obtained in this way also work reasonably well for other test cycles. The proposed procedure was applied in a catalyst screening simulation study that compared the performance of an Fe– and a Cu–zeolite catalyst for a given test cycle. It was demonstrated that each of the two catalysts appeared to have a better performance than the other catalyst when the specified catalyst’s optimized dosing profile was applied to both catalysts. The best catalyst was only identified when comparing both catalysts using their own respective optimized dosing profile. A second simulation study used the proposed dosing procedure to compare catalysts with different ammonia storage capacities. Again, the relative ranking of the catalysts’ performance was shown to depend on the dosing profile. Overall it is demonstrated that the true potential of a catalyst can only be determined when an individually adapted dosing strategy is used.

Oxidation of acrolein to acrylic acid on Mo/V/W-mixed oxide catalysts has been studied by means of the isotopic exchange method steady-state isotopic transient kinetic analysis (SSITKA). As a result of these isotopic exchanges performed with 16O2 and 18O2, some new mechanistic details could be obtained. Acrolein exchanges its oxygen with oxygen of the mixed oxide catalyst. Additionally, the kinetics of the different isotopologues is significantly influenced by oxygen exchange reactions between the surface and the bulk sites. From the SSITKA results, an extended reaction model has been deduced. Thus, the experimentally gained data of the individual isotopologue kinetics could be verified by modeling.

Die hydrothermale Carbonisierung (HTC) ist in Hinblick auf die energetische Verwertung von Biomasse eine vielversprechende Methode. Trotz der langen Historie dieses Verfahrens sind Mechanismus und Kinetik nur unzureichend verstanden. In den hier vorgestellten Experimenten wurde mithilfe der Kombination von Analysenmethoden die Umsetzung von Kohlenhydraten mit sauren und basischen Zusatzen untersucht. Dabei konnte vor allem der Einfluss von Saure auf die Hydrolyse von Cellulose beobachtet werden. Die HTC von Glucose hingegen bleibt weitestgehend von den Zusatzen wie Saure oder Base unbeeinflusst. Durch Veranderung der Reaktionsbedingungen wie der Heizrate konnen die Biokohle-Eigenschaften wie z. B. die Aciditat der Kohle variiert werden. In terms of energy recovery, the hydrothermal carbonization (HTC) is a promising method. Despite the long history of this process, the mechanism and kinetics are poorly understood. For tracing the reaction kinetics a combination of analysis methods has been used. In the presented study the HTC of carbohydrates is examined with addition of acid and base. Thereby, a major influence of acids on the hydrolysis of cellulose can be observed. The HTC of glucose, however, remains largely unaffected by these additives. Furthermore, it was observed that reduced heating rates lead to changes in the biochar acidity.

Mittels der Isotopenaustauschmethode SSITKA (steady-state isotopic-transient kinetic analysis) ergaben sich Ruckschlusse zum Mechanismus der Partialoxidation von Acrolein zu Acrylsaure an Mo/V/W-Mischoxidkatalysatoren. Der Isotopenaustausch erfolgte mit den beiden Sauerstoffisotopen 16O2 und 18O2. Dabei findet am Katalysator ein Austausch des Carbonylsauerstoffs im Acrolein mit Festkorpersauerstoff statt. Zusatzlich wird die Kinetik der unterschiedlichen Isotopologenspezies durch eine Austauschreaktion von Sauerstoff zwischen belegten und unbelegten Zentren an der Oberflache und in der Volumenphase des Katalysators signifikant beeinflusst. Gestutzt durch einen erweiterten Modellvorschlag zum Mechanismus konnten uber Simulationen die experimentell gewonnenen Isotopologenkinetiken verifiziert werden. The partial oxidation of acrolein to acrylic acid on Mo/V/W-mixed oxide catalysts has been studied by means of the isotopic exchange method SSITKA (steady-state isotopic-transient kinetic analysis). In the scope of isotopic exchanges performed with the oxygen isotopes 16O2 and 18O2 some new details could be gained regarding the mechanism. Acrolein exchanges its oxygen with oxygen of the solid catalyst. Additionally the kinetics of the different isotopologues is influenced by another exchange reaction of oxygen between vacant and occupied surface and bulk sites. From the SSITKA results an extended model has been deduced. So, the experimentally gained data of the individual isotopologue kinetics could be verified by simulation.

The setup of a detailed model for the NH3-SCR process on iron exchanged zeolite catalysts is described, which takes into account the reactions of NH3, NO and NO2 occurring under typical exhaust conditions. Validation experiments for a standard SCR gas mixture show that the model is able to describe the dynamic behaviour of this system at transient temperature conditions. The model is used for the parameterization of an ammonia dosing controller. To prove the functionality of this controller it was implemented on a synthetic gas test bench and tested by a dynamic temperature experiment. This setup allows the evaluation of the parameterized controller without any disturbances from engine or injection effects.

The applicability of Mo/V-mixed oxides for the partial oxidation of isobutyraldehyde to methacrolein is examined. The results are compared with the catalytic performance of a heteropolyacid-catalyst.

IR spectroscopy is a well-established method in the characterization of heterogeneous catalysts under reaction conditions. Working in transmission modes is the most common of currently applied technologies. Yet, there are problems inherent in both methods (KBr wafers and self-supporting wafers) for the in-situ investigation of heterogeneously catalyzed reactions. These problems can be avoided by using the DRIFT (diffuse reflection infrared Fourier transformation) spectroscopy. As is shown in this study, DRIFT spectroscopy proves to be a suitable method producing not only qualitative but also quantitative results of in-situ examinations of heterogeneous catalysts.