Metallorganische Gerüstverbindungen (englisch metal–organic frameworks, MOFs) sind aufgrund ihrer hohen Porosität von großem Interesse für eine Vielzahl von Anwendungen in der Katalyse und Gastrennung. Eine begrenzte Anzahl an aktiven Zentren sowie das Verhalten als elektrischer Isolator machen den Einsatz von MOFs als aktives Photokathodenmaterial für die photoelektrokatalytische Wasserstoffproduktion allerdings nicht möglich. Wir berichten hiermit von der Entwicklung eines gestapelten, leitfähigen, zweidimensional-konjugierten MOFs (englisch 2D conjugated MOF, 2D c-MOF) welches aktive sp-Kohlenstoffzentren enthält. Der MOF Cu3HHAE2 basiert auf einem makrozyklischen Aryl-Alkin Liganden, welcher via CuO4 Einheiten verknüpft ist. Dieser sp-Kohlenstoff haltige 2D c-MOF zeigt Halbleitereigenschaften und eine breite Absorption bis in den nah-infraroten Bereich (1600 nm). Erstmalig kann dank der hohen Anzahl an Dreifachbindungen Cu3HHAE2 als MOF-Photokathode für die photoelektrochemische (PEC) Wasserstoffentwicklung verwendet werden. Verglichen mit anderen strukturell definierten, co-Katalysator freien organischen Photokathoden, zeigt er eine Rekordphotostromdichte für die Wasserstoffentwicklung von ≈ 260 μAcm⁻ ² bei 0 V gegen die reversible Wasserstoffelektrode (englisch reversible hydrogen electrode RHE).

La synthèse de l'hydrogène est une alternative viable à l'utilisation du pétrole. Les méthodes telles que l’électrocatalyse font appel à une source d’énergie primaire, ce qui favorise les déchets générés par ces méthodes, de même que le gaspillage d’énergie. Bien qu’ayant de très faibles rendements, les systèmes photocatalytiques permettent la synthèse d’un hydrogène propre et quasi sans déchets. Une perspective permettant d’améliorer encore leur potentiel serait d’éliminer les solvants organiques tels que le DMF, qui sont nocif pour l’environnement et la santé des êtres vivants. Étant donné que le solvant doit être changé, il faut prendre garde à modifier le donneur d’électron sacrificiel et le photosensibilisateur en conséquence. La production de tels solvants est également source de pollution, ce qui atténue le potentiel environnemental de ces méthodes. L’objectif de ce travail est de développer et de tester de nouveaux catalyseurs hydro-solubles variés permettant une amélioration des performances photo-catalytiques actuelles ainsi qu’une performance acceptable dans l’eau. L’étude des propriétés catalytiques est réalisée par l’étude de systèmes homogènes conjugués principalement avec le [Ru(bpy)3]2+ en tant que photosensibilisateur et avec le triethanolamine (dans le DMF) et l’acide ascorbique (dans l’eau) en tant que donneur d’électron sacrificiel. Les catalyseurs présentés lors de ce travail sont des catalyseurs à base de polypyridyl, de cobaloximes et de N-imidoylamidine. Les catalyseurs à base de poly-pyridyl ont d’abord été étudiés puisqu’ils sont réputés pour leur performance en milieux aqueux. La seconde approche consistait à produire des catalyseurs à base de cobaloxime qui aient une performance relativement constante tout d’abord dans les solvants organiques, puis d’adapter ces performances en milieu aqueux. La troisième approche a été de tester des catalyseurs à base de N-imidoylamidine, ce type de catalyseurs n’ayant jamais été testé pour la production d’hydrogène, puis d’en étudier les performances dans l’objectif de paver la voie pour de futures recherches sur le sujet. / The synthesis of hydrogen is a viable alternative to the use of petroleum. Methods such as electrocatalysis use a primary energy source, which reduces the waste generated by these methods, as well as the waste of energy. Although having very low yields, photocatalytic systems allow the synthesis of clean hydrogen with virtually no waste. One prospect to further improve their potential would be to eliminate organic solvents such as DMF, which are harmful to the environment and the health of living beings. Giving the fact that we change the solvent, we need to change the electron sacrificial donor and the photosensitizer as well. The production of such solvents is also a source of pollution, which reduces the environmental potential of these methods. The objective of this work is to develop and test various new water-soluble catalysts allowing an improvement of the current photo-catalytic performances as well as an acceptable performance in water. The study of the catalytic properties is carried out by the study of homogeneous conjugated systems mainly with [Ru(bpy)3]2+ as photosensitizer and with triethanolamine (in DMF) and ascorbic acid (in water) as a sacrificial electron donor. The catalysts presented during this work are catalysts based on polypyridyl, cobaloximes, and N-imidoylamidine. Poly-pyridyl-based catalysts were first studied because they are known for their performance in aqueous media. The second approach was to produce cobaloxime-based catalysts that had relatively constant performance first in organic solvents and then to match this performance in aqueous media. The third approach was to test catalysts based on N-imidoylamidine, as this type of catalyst have never been tested to produce hydrogen, then to study their performance to pave the way for future research on the subject.

The present work focuses on the study of biomass gasification process for generating hydrogen rich synthetic gas with oxy-steam as reactants using experiments and modeling studies. Utilization of the syngas as a fuel in general applications like fuel cells, Fischer-Tropsch FT) process and production of various chemicals like DME, etc. are being considered to meet the demand for clean energy. This study comprises of experiments using an open top down draft reactor with oxygen and steam as reactants in the co-current configuration. Apart from the standard gasification performance evaluation; parametric study using equivalence ratio, steam-to-biomass ratio as major variables towards generation of syngas is addressed towards controlling H2/CO ratio. The gasification process is modeled as a packed bed reactor to predict the exit gas composition, propagation rate, bed temperature as a function of input reactants, temperature and mass flux with variation in thermo-physical properties of biomass. These results are compared with the present experiments as well as those in literature. Experiments are conducted using modified open top downdraft configuration reactor with lock hoppers and provision for oxy-steam injection, and the exit gas is connected to the cooling and cleaning system. The fully instrumented system is used to measure bed temperatures, steam and exit gas temperature, pressures at various locations, flow rates of fuel, reactants and product gas along with the gas composition. Preliminary investigations focused on using air as the reactant and towards establishing the packed bed performance by comparing with the experimental results from the literature and extended the study to O2-N2 mixtures. The study focuses on determining the propagation rate of the flame front in the packed bed reactor for various operating conditions. O2 is varied between 20-100% (vol.) in a mixture of O2-N2 to study the effect of O2 fraction on flame propagation rate and biomass conversion. With the increase in O2 fraction, the propagation rates are found to be very high and reaching over 10 mm/s, resulting in incomplete pyrolysis and poor biomass conversion. The flame propagation rate is found to vary with oxygen volume fraction as XO22.5, and stable operation is achieved with O2 fraction below 30%. Towards introducing H2O as a reactant for enhancing the hydrogen content in the syngas and also to reduce the propagation rates at higher ER, wet biomass is used. Stable operating conditions are achieved using wet biomass with moisture-to-biomass (H2O:Biomass) ratio between 0.6 to 1.1 (mass basis) and H2 yield up to 63 g/kg of dry biomass amounting to 33% volume fraction in the syngas. Identifying the limitation on the hydrogen yield and the criticality of achieving high quality gas; oxy-steam mixture is introduced as reactants with dry biomass as fuel. An electric boiler along with a superheater is used to generate superheated steam upto 700 K and pressure in the range of 0.4 MPa. Steam-to-biomass ratio (SBR) and ER is varied with towards generating hydrogen rich syngas with sustained continuous operation of oxy-steam gasification of dry biomass. The results are analysed with the variation of SBR for flame propagation rates, calorific value of product syngas, energy efficiency, H2 yield per kg of biomass and H2/CO ratio. Hydrogen yield of 104 g per kg of dry casuarina wood is achieved amounting to 50.5% volume fraction in dry syngas through oxy-steam gasification process compared to air gasification hydrogen yield of about 40 g per kg of fuel and 20% volume fraction. First and second law analysis for energy and exergy efficiency evaluation has been performed on the experimental results and compared with air gasification. Individual components of the energy input and output are analysed and discussed. H2 yield is found to increase with SBR with the reduction in energy density of syngas and also energy efficiency. Highest energy efficiency of 80.3% has been achieved at SBR of 0.75 (on molar basis) with H2 yield of 66 g/kg of biomass and LHV of 8.9 MJ/Nm3; whereas H2 yield of 104 g/kg of biomass is achieved at SBR of 2.7 with the lower efficiency of 65.6% and LHV of 7.4 MJ/Nm3. The energy density of the syngas achieved in the present study is roughly double compared to the LHV of typical product gas with air gasification. Elemental mass balance technique has been employed to identify carbon boundary at an SBR of 1.5. Controlling parameters for arriving at the desired H2/CO ratio in the product syngas have been identified. Optimum process parameters (ER and SBR) has been identified through experimental studies for sustained continuous oxy-steam gasification process, maximizing H2 yield, controlling the H2/CO ratio, high energy efficiency and high energy density in the product syngas. Increase in ER with SBR is required to compensate the reduction in O2 fraction in oxy-steam mixture and to maintain the desired bed temperature in the combustion zone. In the range of SBR of 0.75 to 2.7, ER requirement increases from 0.18 to 0.3. The sustained continuous operation is possible upto SBR of 1.5, till the carbon boundary is reached. Operating at high SBR is required for high H2 yield but sustained highest H2 yield is obtained as SBR of 1.5. H2/CO ratio in the syngas increases from 1.5 to 4 with the SBR and depending on the requirement of the downstream process (eg., FT synthesis), suitable SBR and ER combination is suggested. To obtain high energy density in syngas and high energy efficiency, operations at lower SBR is recommended. The modeling study is the extension of the work carried by Dasappa (1999) by incorporating wood pyrolysis model into the single particle and volatile combustion for the packed bed of particles. The packed bed reactor model comprises of array of single particles stacked in a vertical bed that deals with the detailed reaction rates along with the porous char spheres and thermo-physical phenomenon governed by the mass, species and energy conservation equations. Towards validating the pyrolysis and single particle conversion process, separate analysis and parametric study addressing the effects of thermo-physical parameters like particle size, density and thermal conductivity under varying conditions have been studied and compared with the available results from literature. It has been found that the devolatilisation time of particle (tc) follows closely the relationship with the particle diameter (d), thermal conductivity (k), density () and temperature (T) as: The complete combustion of a single particle flaming pyrolysis and char combustion has been studied and validated with the experimental results. For the reactor modeling, energy, mass and species conservation equations in the axial flow direction formulate the governing equations coupled to the detailed single particle analysis. Gas phase reactions involving combustion of volatiles and water gas shift reaction are solved in the packed bed. The model results are compared with the experimental results from wood gasification system with respect to the propagation rate, conversion times, exit gas composition and other bed parameters like conversion, peak bed temperatures, etc. The propagation rates compare well with experimental data over a range of oxygen concentration in the O2- N2 mixture, with a peak at 10 mm/s for 100 % O2. In the case of oxy-steam gasification of dry biomass, the results clearly suggest that the char conversion is an important component contributing to the bed movement and hence the overall effective propagation rate is an important parameter for co-current reactors. This is further analyzed using the carbon boundary points based on elemental balance technique. The model predictions for the exit gas composition from the oxy-steam gasification matches well with the experimental results over a wide range of equivalence ratio and steam to biomass ratio. The output gas composition and propagation rates are found to be a direct consequence of input mass flux and O2 fraction in oxy-steam mixture. The present study comprehensively addresses the oxy-steam gasification towards generating hydrogen rich syngas using experimental and model studies. The study also arrives at the parameters for design consideration towards operating an oxy-steam biomass gasification system. The following flow chart provides the overall aspects that are covered in the thesis chapter wise.

Erdöl und Erdgas liegen als flüssige Kohlenwasserstoffe in porösen Sedimentgesteinen im geologischen Untergrund vor. Um diese Kohlenwasserstoffe zu gewinnen, wird der Untergrund durch Tiefbohrungen zur Förderung erschlossen. Anschließend erfolgt die Förderung des Erdöls in drei Phasen: der Primär-, Sekundär- und Tertiärförderung. In der primären Phase wird Erdöl durch den Druck in der Lagerstätte gewonnen, in der sekundären Phase durch künstliche Aufrechterhaltung des Drucks und in der tertiären Phase durch technische Beeinflussung der strömungsmechanischen und thermodynamischen Eigenschaften des Erdöls. Dennoch verbleibt insbesondere bei Schweröllagerstätten ein Anteil von 45 bis 90 % des ursprünglich in der Lagerstätte vorhandenen Erdöls in der Lagerstätte. Aufgrund strömungsmechanischer und thermodynamischer Einschränkungen ist eine Gewinnung dieses Anteils technisch und/oder wirtschaftlich nicht möglich. Meist wird die Lagerstätte nach Abschluss der Förderung verfüllt und die übertägigen Anlagen zurückgebaut. Zugleich steigt weltweit der Bedarf an Energiequellen, insbesondere an solchen, die für die Dekarbonisierung und Umstellung auf umweltschonende Energien benötigt werden. Wasserstoff wird voraussichtlich als chemischer Energieträger der zukünftige Schlüsselrohstoff für die Energiewende sein. Diese Forschungsarbeit untersucht die Weiternutzung bzw. Erschließung ausgeförderter Erdöllagerstätten zur Wasserstoffgewinnungmittels thermischer Verfahren. Diese Verfahren orientieren sich an bereits etablierten Methoden für die übertägige Verfahrenstechnik. Durch das Verfahren wird die Lagerstätte mithilfe der Verbrennung des in dieser vorhandenen Restöls erhitzt und das entstehende Koks durch eine Wasserinjektion in Synthesegas umzuwandeln. Durch die hohen Temperaturen entsteht in der Lagerstätte eine Atmosphäre aus Wasserdampf, die zur Vergasung des Kokses führt. Das Gas wird durch die Wasserfront aus der Lagerstätte in die Produktionsbohrungen verdrängt und kann anschließend an der Oberfläche aufbereitet werden. Im Kontext der Lagerstättenprozesse entsteht nicht nur Wasserstoff, sondern auch weitere Verbrennungsprodukte wie Kohlenstoffmonoxid, Kohlenstoffdioxid, Sauergase und Kohlenwasserstoffgase. Diese werden verfahrenstechnisch aufbereitet und dampfreformiert in den obertägigen Anlagen. Zur Erfüllung der Anforderungen an blauen Wasserstoff ist die Reinjektion von Kohlenstoffdioxid erforderlich. In der Dissertation wird ein numerisches Berechnungsschema eingeführt und ausführlich getestet, um die lagerstättentechnische Simulation der thermischen Wasserstoffgewinnung durchzuführen. Anhand von Modelllagerstätten werden mithilfe dieses Schemas relevante Prozessparameter ermittelt und für die Übertragung auf die konkrete Lagerstättensimulation aufbereitet. Das Verfahren zur Wasserstoffförderung wird an einer antiklinalen Lagerstätte mit geostatistischer Heterogenität simuliert. Die Ergebnisse werden zur weiteren Auswertung bezüglich Integritätsfragen, Übertageanlagen sowie wirtschaftlicher und strategischer Aspekte herangezogen.