Browsing by Author "Dyballa, Michael"

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Open Access
Aktivierte Modifikation der Träger‐Metall‐Wechselwirkungen als Schlüssel für hochaktive Ru/γ‐Al2O3‐Katalysatoren für die COx‐Methanisierung
(2020) Chen, Shilong; Abdel‐Mageed, Ali M.; Dyballa, Michael; Parlinska‐Wojtan, Magdalena; Bansmann, Joachim; Pollastri, Simone; Olivi, Luca; Aquilanti, Giuliana; Behm, R. Jürgen
Ru/Al2O3 ist ein außerordentlich stabiler, aber weniger aktiver Katalysator für Methanisierungs-Reaktionen. Hier berichten wir über einen neuartigen Ansatz, mit dem die Aktivität dieser Katalysatoren bei der Methanisierung von CO2 in CO2/H2-Gemischen erheblich gesteigert werden kann. Hochaktive und -stabile Ru/γ-Al2O3-Katalysatoren wurden über eine Hochtemperatur-Behandlung im reduktiven Reaktionsgasgemisch erhalten. Operando/In-situ-Spektroskopie und Rastertransmissionselektronenmikroskopie (STEM)-Abbildungen zeigen, dass die deutlich erhöhte Aktivität für die Methanisierung von CO bzw. CO2 mit einer Abflachung der Ru-Nanopartikel und der Bildung von stark basischen Plätzen auf dem hydroxylierten Aluminiumoxid einhergeht. Die erhöhte Aktivität der Katalysatoren um Faktoren von 5 (CO) bzw. 14 (CO2) führen wir auf eine aktivierte Modifikation der Träger-Metall-Wechselwirkungen zurück, die durch eine reaktive Modifizierung der Al2O3-Oberfläche im Reaktionsgas und eine erhöhte thermische Mobilität der Ru-Nanopartikel verursacht wird.
Open Access
Comprehensive characterization and evaluation of the process chain and products from Euphausia superba exocuticles to chitosan
(2023) Hahn, Thomas; Egger, Jeannine; Krake, Simon; Dyballa, Michael; Stegbauer, Linus; Seggern, Nils von; Bruheim, Inge; Zibek, Susanne
Antarctic krill (Euphausia superba) is a source for compounds of high nutritive value. Within that process of extraction, exocuticles (shells) accumulate which are currently disposed. A valorization of the compounds of the exocuticle such as chitosan would be beneficial to avoid waste and to obtain a versatile polymer at the same time. In contrast to previous investigations focusing on chitosan production from whole krill, we applied and optimized process stages of the chitosan production from the exocuticles, performing a comprehensive analytical evaluation of the whole process, the side streams and the products for the first time. Degreasing was the first step resulting in a krill oil yield of 6.2% using ethanol. The fatty acid profile exhibited high contents of phospholipids (21.2%). Citric acid offered a demineralization efficiency of 93%. Deproteinization investigation revealed 2 M NaOH and 90°C for 2.5 h to be the best parameters, resulting in a deproteinization efficiency of 99.9% and a chitin content of 92.8%. The spectroscopic investigation indicated that the chitin has a crystallinity index of 76% and an acetylation degree of 88%. The deacetylation degrees of the resulting chitosans is determined to be 74%-88%, the molecular weight ranges from 102 to 126 kDa.
Open Access
Cu(dppf) complexes can be synthesized from Cu-exchanged solids and enable a quantification of the Cu-accessibility by 31P MAS NMR spectroscopy
(2024) Kaya, Elif; Dittmann, Daniel; Schmidt, Maximilian; Dyballa, Michael
Herein, we apply three different copper-exchanged materials (Na-[Al]SBA-15, silica, Na-MCM-22) as hosts for a direct synthesis of CuI(1,1'-bis(diphenylphosphino)ferrocene = dppf) complexes in cationic ion exchange position. Using 31P MAS NMR spectroscopy, we show that identical complexes as after ion exchange are generated if the solids are applied as reactants directly. The homogeneity of copper exchanges is evaluated by EDX spectroscopy. Both CuI and CuII result in the formation of complexes, thereby oxidizing dppf. Cu-particles were not reactive. Optimized conditions for a maximized complex formation are identified applying quantitative 31P MAS NMR spectroscopy and ICP-OES. Only accessible copper in cationic position of the solids forms the complexes. This enables a quantification of the amount of copper in mesopores vs. the total copper amount. Thus, besides a new synthesis of the complex a suitable method for quantitative elucidation of the location of copper cations is demonstrated herein.
Open Access
Desilicated ZSM‐5 catalysts : properties and ethanol to aromatics (ETA) performance
(2023) Dittmann, Daniel; Kaya, Elif; Dyballa, Michael
Herein, desilication in increasingly harsh conditions was used to introduce mesopores into two different industrial ZSM‐5 catalysts (Si/Al ratio 11 or 29). For desilicated samples, increasing BET surface areas, mesopore volumes, and Si(OH) densities were noted. Brønsted acid site (BAS) densities increased upon desilication, as formerly inaccessible BAS in blocked pores became available, while the strength of the BAS was maintained upon desilication. Using KOH instead of NaOH as desilication agent can increase the mesopore volume generated per mass loss. The correlations between desilication strength and properties were largely determined by the parent Si/Al ratio. In general the introduced mesopores increased lifetimes in the ETA conversion, while additional Si(OH) groups introduced by desilication reduce the lifetime again. The lifetime is thus determined by a complex interplay of BAS density, improved reactant transport by introduced mesopores and Si(OH) density. There were no additional aromatics formed in desilicated samples during the conversion of ethanol and the samples were, in terms of aromatic yield, outperformed by a microporous parent. However, as result of longer lifetimes less ethanol was lost due to coke formation. It is concluded that desilication should be combined with other post‐modifications to increase aromatic production and lifetime.
Open Access
Effect of aluminum and sodium on the sorption of water and methanol in microporous MFI-type zeolites and mesoporous SBA-15 materials
(2020) Li, Zheng; Rieg, Carolin; Beurer, Ann-Katrin; Benz, Michael; Bender, Johannes; Schneck, Christof; Traa, Yvonne; Dyballa, Michael; Hunger, Michael
The interaction and nature of surface sites for water and methanol sorption on MFI-type zeolites and mesoporous SBA-15 were investigated by solid-state NMR spectroscopy and correlated with the desorption enthalpies determined via TGA/DSC. For siliceous Silicalite-1, 29Si CPMAS NMR studies support stronger methanol than water interactions with SiOH groups of Q3-type. On siliceous SBA-15, SiOH groups of Q2-type are accompanied by an enhanced hydrophilicity. In aluminum-containing Na-ZSM-5, Na+ cations are strong adsorption sites for water and methanol as evidenced by 23Na MAS NMR in agreement with high desorption enthalpies of ΔH = 66-74 kJ/mol. Solid-state NMR of aluminum-containing Na-[Al]SBA-15, in contrast, has shown negligible water and methanol interactions with sodium and aluminum. Desorption enthalpies of ΔH = 44-60 kJ/mol hint at adsorption sites consisting of SiOH groups influenced by distant framework aluminum. On H-ZSM-5, Brønsted acidic OH groups are strong adsorption sites as indicated by partial protonation of water and methanol causing low-field shifts of their 1H MAS NMR signals and enhanced desorption enthalpies. Due to the small number of Brønsted acid sites in aluminum-containing H-[Al]SBA-15, water and methanol adsorption on this material is suggested to mainly occur at SiOH groups with distant framework aluminum species, as in the case of Na-[Al]SBA-15.
Open Access
Efficient and spatially controlled functionalization of SBA‐15 and initial results in asymmetric Rh‐catalyzed 1,2‐additions under confinement
(2021) Beurer, Ann‐Katrin; Kirchhof, Manuel; Bruckner, Johanna R.; Frey, Wolfgang; Baro, Angelika; Dyballa, Michael; Giesselmann, Frank; Laschat, Sabine; Traa, Yvonne
Selectively functionalized mesoporous silica may considerably advance heterogeneous catalysis through the controlled immobilization of highly selective complex catalysts inside the mesopores. However, spatially controlled functionalization and the precise analytical verification are still a challenge. In this publication, we report a method, which ensures a selective functionalization of the mesopore surface with a clickable linker and thus makes it possible to study confinement effects during catalyzed reactions. First, we passivate the silanol groups on the particle surface and in the pore entrances of the mesoporous silica material SBA‐15 with 1,1,1‐trimethyl‐N‐(trimethylsilyl)silanamine. Then we remove the template by solvent extraction and functionalize the pore walls with 3‐azidopropyltriethoxysilane before we click the catalyst. In initial experiments of asymmetric Rh‐catalyzed 1,2‐addition, we investigate the performance of a catalyst clicked selectively in the mesopores and compare it to the dissolved catalyst as well as to the catalyst immobilized exclusively on the external surface of SBA‐15.
Open Access
Die Entwicklung neuer Zeolithkatalysatoren für die Methanol-zu-Olefin-Umsetzung
(2015) Dyballa, Michael; Hunger, Michael (Prof. Dr.)
In dieser Arbeit wurden verschiedene 10-Ring-Zeolith-Katalysatoren untersucht. Das Ziel war, den Anteil an Propen in der Produktverteilung der Methanol-zu-Olefin-Umwandlung (MTO) zu erhöhen. Es wurde festgestellt, dass die Produktverteilung stark von der Säurezentrendichte der Katalysatoren abhing. Je nach Porensystem wurde ein idealer Säurezentrendichtebereich identifiziert. In diesem Bereich waren sowohl Propenanteil als auch Katalysatorlebensdauer hoch. Parallel dazu wurden weniger Alkane, Ethen und Aromaten gebildet und die Koksbildung wurde minimiert. Auch die Modifizierung der 10-Ring-Zeolithkatalysatoren durch Mesoporen im Zeolithgitter und die Dealuminierung von Zeolithkatalysatoren wurden untersucht. Weitere angewandte Modifizierungen waren die Imprägnierung mit Phosphat, der Einbau von Bor und ein partieller Ionenaustausch. Bei angepasster Temperatur und Katalysatorbelastung wurde so ein Propenanteil von über 50% erreicht.
Open Access
Higher BTEX aromatic yield from ethanol over desilicated H,Zn-[Al]ZSM-5 catalysts
(2024) Dittmann, Daniel; Ileri, Alime; Strassheim, Dennis; Dyballa, Michael
The amount of BTEX aromatics obtained from the conversion of ethanol (ETA) is increased by combining ZSM-5 catalysts having optimum acidity with desilication and zinc ion exchange. Zinc leads to preferred dehydrogenation instead of hydrogen transfer. It decreases the share of paraffin products and increases BTEX contents (up to SBTEX = 50%) at the cost of lifetime. The latter can be increased via desilication. An ethylene feed increases lifetime and BTEX production as result of oxygenate absence. Combination of improvements resulted in a C2 conversion capacity of 206 g g-1 and a total yield of BTEX aromatics of 31.6 g g-1, which is about a factor of 2-3 times better than the respective values found for microporous, mesoporous, or microporous Zn-exchanged materials. In situ UV/vis spectra reveal that desilicated samples coke significantly slower than microporous samples, whereas Zn exchange supports the formation of coke. Thus, by a clever combination of suitable post-modifications, a significantly higher BTEX production from the primary source ethanol can be achieved.
Open Access
Influence of ZSM-5 crystal size on methanol-to-olefin (MTO) vs. ethanol-to-aromatics (ETA) conversion
(2023) Dittmann, Daniel; Kaya, Elif; Strassheim, Dennis; Dyballa, Michael
Crystal size is a key parameter of zeolites applied as catalysts. Herein, ZSM-5 crystals with similar physicochemical and acid properties, few defects, and aluminum exclusively in tetrahedral coordination are synthesized and the influence of the crystal size on the MTO and ETA conversion is investigated. Short olefins are the main products of the MTO conversion, whereas larger olefins and aromatics dominate the products after ETA conversion. In the case of both feeds, an increased crystal size decreases the catalyst’s lifetime. The MTO conversion over larger ZSM-5 altered the product distribution, which was not the case for the ETA conversion. The reason is that the instantly available aromatics during ETA conversion lead to fast coking and zeolite crystals only active in the outer layers. Thus, the different reactivity of different-sized ZSM-5 is direct proof of a different conversion mechanism for both alcohols.
Open Access
Raising the COx methanation activity of a Ru/γ‐Al2O3 catalyst by activated modification of metal-support interactions
(2020) Chen, Shilong; Abdel‐Mageed, Ali M.; Dyballa, Michael; Parlinska‐Wojtan, Magdalena; Bansmann, Joachim; Pollastri, Simone; Olivi, Luca; Aquilanti, Giuliana; Behm, R. Jürgen
Ru/Al2O3 is a highly stable, but less active catalyst for methanation reactions. Herein we report an effective approach to significantly improve its performance in the methanation of CO2/H2 mixtures. Highly active and stable Ru/γ‐Al2O3 catalysts were prepared by high‐temperature treatment in the reductive reaction gas. Operando/in situ spectroscopy and STEM imaging reveals that the strongly improved activity, by factors of 5 and 14 for CO and CO2 methanation, is accompanied by a flattening of the Ru nanoparticles and the formation of highly basic hydroxylated alumina sites. We propose a modification of the metal-support interactions (MSIs) as the origin of the increased activity, caused by modification of the Al2O3 surface in the reductive atmosphere and an increased thermal mobility of the Ru nanoparticles, allowing their transfer to modified surface sites.
Open Access
Sulfur‐composites derived from poly(acrylonitrile) and poly(vinylacetylene) : a comparative study on the role of pyridinic and thioamidic nitrogen
(2023) Kappler, Julian; Klostermann, Sina V.; Lange, Pia L.; Dyballa, Michael; Veith, Lothar; Schleid, Thomas; Weil, Tanja; Kästner, Johannes; Buchmeiser, Michael R.
Sulfurized poly(acrylonitrile) (SPAN) is a prominent example of a highly cycle stable and rate capable sulfur/polymer composite, which is solely based on covalently bound sulfur. However, so far no in‐depth study on the influence of nitrogen in the carbonaceous backbone, to which sulfur in the form of thioketones and poly(sulfides) is attached, exists. Herein, we investigated the role of nitrogen by comparing sulfur/polymer composites derived from nitrogen‐containing poly(acrylonitrile) (PAN) and nitrogen‐free poly(vinylacetylene) (PVac). Results strongly indicate the importance of a nitrogen‐rich, aromatic carbon backbone to ensure full addressability of the polymer‐bound sulfur and its reversible binding to the aromatic backbone, even at high current rates. This study also presents key structures, which are crucial for highly cycle and rate stable S‐composites.