Porosity and Structure of Hierarchically Porous Ni/Al₂O₃ Catalysts for CO₂ Methanation

CO$_{2}$ methanation is often performed on Ni/Al$_{2}$O$_{3}$ catalysts, which can suffer from mass transport limitations and, therefore, decreased efficiency. Here we show the application of a hierarchically porous Ni/Al$_{2}$O$_{2}$ catalyst for methanation of CO$_{2}$. The material has a well-defined and connected meso- and macropore structure with a total porosity of 78%. The pore structure was thoroughly studied with conventional methods, i.e., N$_{2}$ sorption, Hg porosimetry, and He pycnometry, and advanced imaging techniques, i.e., electron tomography and ptychographic X-ray computed tomography. Tomography can quantify the pore system in a manner that is not possible using conventional porosimetry. Macrokinetic simulations were performed based on the measures obtained by porosity analysis. These show the potential benefit of enhanced mass-transfer properties of the hierarchical pore system compared to a pure mesoporous catalyst at industrially relevant conditions. Besides the investigation of the pore system, the catalyst was studied by Rietveld refinement, diffuse reflectance ultraviolet-visible (DRUV/vis) spectroscopy, and H$_{2}$-temperature programmed reduction (TPR), showing a high reduction temperature required for activation due to structural incorporation of Ni into the transition alumina. The reduced hierarchically porous Ni/Al$_{2}$O$_{3}$ catalyst is highly active in CO$_{2}$ methanation, showing comparable conversion and selectivity for CH$_{4}$ to an industrial reference catalyst

Porosity and Structure of Hierarchically Porous Ni/Al₂O₃ Catalysts for CO₂ Methanation

CO₂ methanation is often performed on Ni/Al₂O₃ catalysts, which can suffer from mass transport limitations and, therefore, decreased efficiency. Here we show the application of a hierarchically porous Ni/Al₂O₃ catalyst for methanation of CO₂. The material has a well-defined and connected meso- and macropore structure with a total porosity of 78%. The pore structure was thoroughly studied with conventional methods, i.e., N₂ sorption, Hg porosimetry, and He pycnometry, and advanced imaging techniques, i.e., electron tomography and ptychographic X-ray computed tomography. Tomography can quantify the pore system in a manner that is not possible using conventional porosimetry. Macrokinetic simulations were performed based on the measures obtained by porosity analysis. These show the potential benefit of enhanced mass-transfer properties of the hierarchical pore system compared to a pure mesoporous catalyst at industrially relevant conditions. Besides the investigation of the pore system, the catalyst was studied by Rietveld refinement, diffuse reflectance ultraviolet-visible (DRUV/vis) spectroscopy, and H₂-temperature programmed reduction (TPR), showing a high reduction temperature required for activation due to structural incorporation of Ni into the transition alumina. The reduced hierarchically porous Ni/Al₂O₃ catalyst is highly active in CO₂ methanation, showing comparable conversion and selectivity for CH₄ to an industrial reference catalyst

Carotenoid Production Process Using Green Microalgae of the <i>Dunaliella</i> Genus: Model-Based Analysis of Interspecies Variability

The engineering of photosynthetic bioprocesses is associated with many hurdles due to limited mechanistic knowledge and inherent biological variability. Because of their ability to accumulate high amounts of β-carotene, green microalgae of the <i>Dunaliella</i> genus are of high commercial relevance for the production of food, feed, and high-value fine chemicals. This work aims at investigating the interspecies differences between two industrially relevant <i>Dunaliella</i> species, namely <i>D. salina</i> and <i>D. parva</i>. A systematic work flow composed of experiments and mathematical modeling was developed and applied to both species. The approach combining flow cytometry and pulse amplitude modulation (PAM) fluorometry with biochemical methods enabled a coherent view on the metabolism during the adaptational stress response of <i>Dunaliella</i> under carotenogenic conditions. The experimental data was used to formulate a dynamic-kinetic reactor model that covered the effects of light and nutrient availability on biomass growth, internal nutrient status, and pigment fraction in the biomass. Profile likelihood analysis was performed to ensure the identifiability of the model parameters and to point out targets for model reduction. The experimental and computational results revealed significant variability between <i>D. salina</i> and <i>D. parva</i> in terms of morphology, biomass, and β-carotene productivity as well as differences in photoacclimation and photoinhibition. The synergistic approach combining experimental and mathematical methods provides a systems-level understanding of the microalgal carotenogenesis under fluctuating environmental conditions and thereby drive the development of sustainable and economically feasible phototrophic processes