Michael Dyballa

Universität Stuttgart · Insitute of Chemical Technology

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 contras...

In molecular heterogeneous catalysis knowledge about the location and accessibility of the immobilized metal complex inside porous solids is important to assess the catalytic efficiency. Here we developed a method...

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...

Many Cu catalyzed ATRC reactions suffer from low catalyst activity and stability. We synthesize five 1,10-phenanthroline ligands substituted in the 5-position with α-aminophosphonate groups, through which the corresponding Cu complexes...

Organometallic complexes are frequently deposited on solid surfaces, but little is known about how the resulting complex-solid interactions alter their properties. Here, a series of complexes of the type Cu(dppf)(Lx)+ (dppf = 1,1'-bis(diphenylphosphino)ferrocene, Lx = mono- and bidentate ligands) were synthesized, physisorbed, ion-exchanged, or cov...

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, exi...

Trimethylphosphine (TMP) is demonstrated as a suitable ³¹P MAS NMR probe molecule for determining accessibility, environment, and spatial distribution of oxidation-active oxidic metal species on solid catalysts quantitatively. It oxidizes to trimethylphosphine oxide (TMPO) at oxygen donor sites, which is demonstrated for oxides of copper, manganese...

Water and alcohols like methanol are key substrates in catalysis. Thus, adsorption on catalysts plays a key role in chemical reactions. Herein we investigate how surface sites and confinement influence the formation of water surface species, their adsorption strength, and complex stability. We compare adsorption on microporous MFI zeolites, mesopor...

We herein investigate methanol adsorbates on a variety of heterogeneous catalysts. We quantitatively desorb methanol from saturated MFI zeolites, SBA-15 materials and silicotungstic acid (STA) supported on silica, all in the respective siliceous, Na- and H-forms. Surface species are identified by ¹H and ¹³C MAS NMR and DRIFTS. On saturated surfaces...

Biochar is a promising material for environmental amendment. However, the adsorption mechanism of nitrogen-based ionic species, particularly the pH dependence, is still under debate because of its high susceptibility to experimental conditions. In this study, the adsorption of ammonium sulfate by rice-husk biochar produced by low-temperature carbon...

As a commercial MTO catalyst, SAPO-34 zeolite exhibits excellent recyclability probably due to its intrinsic good hydrothermal stability. However, the structural dynamic changes of SAPO-34 catalyst induced by hydrocarbon pool (HP) species and the water formed during the MTO conversion as well as its long-term stability after continuous regeneration...

We compare three methods for quantitatively distinguishing the location of noble metals (NM) in mesopores from those found on the external particle surface. MCM‐41 and SBA‐15 with NM either preferentially located in mesopores or on the external surface were prepared and characterized by TEM. We quantified arylphosphines forming complexes with NM by...

We herein investigate the alumination mechanism of siliceous micro- and mesoporous materials (SBA-15, SBA-16, and dealuminated Y-zeolite) with NaAlO2 to synthesize new ion exchangers and acid catalysts. We show that in aqueous alkaline solution, the materials' surface is partially dissolved to form Si(OH)x groups (x = 1, 2, 3) that react with tetra...

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...

Carbon recycling reusing emitted carbon dioxide (CO2) as raw materials is nowadays recognized as a concept ahead of CO2 capture and storage for controlling its emission to the air. Here, recently discovered alkali-metal-based instantaneous ex situ mineral carbonation under ambient conditions is studied for saponite clay nanoparticles. The cationic...

In this paper, both volatile and strongly adsorbed products of heavy hydrocarbon conversion on a zeolite were investigated by gas‐phase and solid‐state NMR. For this purpose, the reactions were carried out in sealed glass tubes under vacuum to collect the volatile reaction products. This procedure is demonstrated for pure 2‐ethylphenol conversion o...

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...

We herein investigate the selective dehydration of ethanol at high conversions (>99.5%) at a moderate reaction temperature of only 493 K over a catalyst of silicotungstic acid (STA) supported on...

Herein, we describe a method for the quantification of Brønsted acid sites located on surfaces and in pores of hierarchical zeolite catalysts. The probe triphenylphosphine (TPP) accesses only pores bigger 0.72 nm. The signal of protonated TPP is baseline separated from other signals and can be directly quantified by 31P MAS NMR spectroscopy. Result...

Different phosphines (PR3, R = phenyl, 4-methoxyphenyl) are demonstrated to be useful probe molecules for the spatial location and quantification of noble metal (NM) atoms within mesoporous and microporous support materials, such as silica A200, mesoporous SBA-15, and different zeolites Y. For this purpose, the high NMR sensitivity of ³¹P nuclei (s...

Ru/Al2O3 is a highly stable, but less active catalyst for methanation reactions. Here 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...

Ru/Al2O3 ist ein außerordentlich stabiler, aber weniger aktiver Katalysator für Methanisierungs-Reaktionen. Hier berichten wir über einen neuartigen Ansatz, mit dem die katalytische Aktivität dieser Katalysatoren bei der Methanisierung von CO2 in CO2/H2 Gemischen erheblich gesteigert werden kann. Hochaktive und –stabile Ru/γ-Al2O3 Katalysatoren wur...

The direct conversion of methane to methanol has the potential of substantially reducing methane emissions and flaring, as such a process might provide an alternative for remote natural gas locations. In this report, we investigate the performance of a range of Cu exchanged mordenite zeolites are active materials for such a reaction, employing a st...

On our route towards a more sustainable future, the use of stranded and underutilized natural gas to produce chemicals would be a great aid in mitigating climate change, due to the reduced CO2 emissions in comparison to using petroleum. In this study, we investigate the performance of Cu-exchanged SSZ-13 and SAPO-34 microporous materials in the ste...

The synthesis of macrocycles is severely impeded by concomitant oligomer formation. Here, we present a biomimetic approach that utilizes spatial confinement to increase macrocyclization selectivity in the ring clos-ing metathesis of various dienes at elevated substrate concentration up to 25 mM using an olefin me-tathesis catalyst selectively immob...

The direct methane to methanol (DMTM) conversion is often referred to as a ‘dream reaction’ with enormous potential to alter energy sector and chemical industry. After O2-activation, Cu-exchanged zeolites form CuxOy species that activate CH4 and release it in the form of CH3OH upon interaction with H2O. Despite extensive research efforts in the las...

Triphenylphosphine (PPh3) is demonstrated to be a useful molecular probe and tool for quantitatively characterizing the spatial distribution of noble metals on porous supports. The preparation of metal organic complexes by loading the supports with PPh3 was performed by physically mixing the water-free catalysts with solid PPh3 powder in nitrogen a...

The direct stepwise transformation of CH4 to CH3OH over Cu-exchanged zeolites has been an intensively researched reaction as it can provide a solution for the utilization of this abundant feedstock. Up to date a commercial process is far from realization, which is why an understanding of the Cu speciation in zeolites as a function of reaction condi...

This contribution clarifies the overoxidation‐preventing key step in the methane‐to‐methanol (MTM) conversion over copper mordenite zeolites. We followed the methane‐to‐methanol conversion over copper mordenite zeolites by NMR supported by DRIFTS to show that surface methoxy groups (SMGs) located at zeolite Brønsted sites are the key intermediates....

The active site in ethene oligomerization catalyzed by Ni-zeolites is proposed to be a mobile Ni(II) complex, based on density functional theory-based molecular dynamics (DFT-MD) simulations corroborated by continuous-flow experiments on Ni-SSZ-24 zeolite. The results of the simulations at operating conditions show that ethene molecules reversibly...

Herein we investigate the activity of copper mordenites in the methane-to-methanol conversion and the material de- and realumination. From four parent materials, a library of copper mordenites was synthesized by liquid and solid state ion exchange techniques. Two key properties govern the activity of these materials in the methane conversion: the p...

ZSM-23 (MTT) is a silicon-rich zeolite with one-dimensional, 10-membered ring channels, which has recently attracted interest as a promising catalyst in aromatic-free methanol-to-hydrocarbons conversion. To obtain a better understanding of the catalytic activity and ultimately to design a better catalyst, it is crucial to locate the active sites in...

Cu‐exchanged zeolites with the Ferrierite topology were investigated in the direct CH4 to CH3OH conversion. Samples with a systematic compositional variation in terms of Na/Al and Cu/Al ratios where synthesized by liquid ion exchange. The presence of Na is observed to be beneficial for the Cu exchange and thereby higher Cu loadings were achieved. T...

The direct conversion of methane to methanol (MTM) is a reaction which has the potential to disrupt great part of the synthesis gas derived chemical industry. However, despite many decades of research, active enough catalysts and suitable processes for industrial application are still not available. Recently, several copper-exchanged zeolites have...

The reactivity of partially alkali metal ion-exchanged X,H-ZSM-5 (X = Li, Na, Cs) catalysts was evaluated in methanol-to-olefin (MTO) conversion. ¹H MAS NMR spectroscopy using acetonitrile-d3 and ammonia as probes revealed decreased Brønsted acid site density (ASD) and maintained acid site strength of alkali metal ion-exchanged X,H-ZSM-5 catalysts....

The local structural and electronic properties of Cu sites during the direct conversion of methane to methanol with molecular oxygen was followed by X-ray absorption spectroscopy (XAS) on a set of Cu-zeolites with different topology (large pore MOR and small pore CHA frameworks) and similar chemical composition (Si/Al ∼ 11 and 12, respectively). Tw...

This work describes the synthesis and investigation of improved SUZ-4 catalysts (SZR framework) and their application in methanol-to-olefins and methane-to-methanol conversion. We report boron containing, dealuminated and desilicated SUZ-4 catalysts. Ammonia and pyridine probe molecules enabled the assignment of acid site densities to the 10-MR and...

ZSM-5 is a widely used zeolite catalyst and is employed industrially for the Methanol to Gasoline (MTG) process. Even so, deactivation of ZSM-5 by coke formation constitutes a major technical and also fundamental challenge. We investigate the deactivation of a range of ZSM-5 catalysts through catalytic testing, physico-chemical characterization and...

Cu-exchanged zeolites possess active sites able to cleave the C−H bond of methane at temperatures ≤200 °C, enabling its selective partial oxidation to methanol. Herein we explore this process over Cu-SSZ-13 materials. We combine activity tests and X-Ray Absorption Spectroscopy (XAS) to thoroughly investigate the influence of reaction parameters and...

In this study Cu-SSZ-13 catalysts have been investigated for the partial methane oxidation to methanol. The parameters involved in the three step stoichiometric process were thoroughly investigated with respect to methanol yield. Operando X-Ray Absorption Spectroscopy at the Cu K-Edge was utilized to follow the Cu speciation during the process.

Low-silica AlPO-34 materials with similar crystal sizes but different Brønsted acid site densities were prepared and investigated as catalysts in methanol-to-olefin (MTO) conversion. The effect of Brønsted acid site density on catalyst activity and the dominant reaction mechanism during the MTO conversion was investigated via TGA, GC-MS, solid-stat...

Microporous ZSM-22 zeolites (structure type TON) were modified by treatments with different alkaline solutions for introducing mesopores. This surprisingly affected the nature and the density of both SiOH groups and Brønsted acid sites significantly, while the Brønsted acid strength was maintained. The catalyst lifetime in the methanol-to-olefin (M...

The intrinsic hydrogenation activities of homologous series of noble metal-containing zeolites Y were studied by in situ solid-state NMR spectroscopy under semi-batch conditions. For the hydrogenation of acrylonitrile, reaction rates in the sequence Pd/H,Na-Y > Rh/H,Na-Y > Pt/H,Na-Y > Ir/H,Na-Y were determined. The dehydrogenation of propane at the...

Zeolites ZSM-5, ZSM-11, and ZSM-22 (nSi/nAl = 20-1000) were applied as methanol-to-olefin conversion (MTO) catalysts and optimized for high propene selectivities at high methanol conversions, high weight hourly space velocities, and for long catalyst lifetimes. On zeolites ZSM-5 and ZSM-11 with optimized Brønsted acid site densities of 0.13 and 0.1...

A series of FAU, MFI, and MOR Na-zeolites with different nSi/nAl ratios and varying exchanged cations Li+, Na+, K+ and Cs+ are investigated as catalysts in the gas phase dehydration of lactic acid to acrylic acid. The conversions and selectivities as well as their time dependence prove to be greatly affected by the structure, the type of alkali-met...

It is demonstrated for low-silica zeolite 25NH4,Na-A (nSi/nAl = 1.0) with an ammonium exchange degree of 25% that the formation of acidic bridging OH groups (Si(OH)Al) after thermal deammoniation is accompanied by a weak dealumination of the framework. As the extra-framework aluminum species mainly exist predominantly in the form of Al3+ cations, t...

Experimental evidence for the presence of tert-butyl cations, which are important intermediates in acid-catalyzed heterogeneous reactions, on solid acids has still not been provided to date. By combining density functional theory (DFT) calculations with 1H/13C magic-angle-spinning NMR spectroscopy, the tert-butyl cation was successfully identified...

In the present work, the generation and properties of Brønsted acidic bridging OH groups (Si(OH)Al) in Rh-, Ir-, Pd-, and Pt-containing zeolites Y were quantitatively investigated by multi-nuclear solid-state NMR spectroscopy. The number of Si(OH)Al groups formed per noble metal atom upon their reduction was found to be 0.3 to 1.3 instead of the th...

The formation and evolution of initial reaction intermediates as well as the reaction mechanism during the early period of the methanol conversion on the silicoaluminophosphate SAPO-41 with one-dimensional and 10-numbered ring pore system was elucidated. According to in situ UV–vis spectroscopy, the formation and nature of intermediates formed on t...

Little is known on the early stages of the methanol-to-olefin (MTO) conversion over H-SAPO-34, before the steady-state with highly active polymethylbenzenium cations as most important intermediates is reached. In this work, the formation and evolution of carbenium ions during the early stages of the MTO conversion on a H-SAPO-34 model catalyst were...

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 Säurezentren...

Quantitative 17O MAS NMR investigation of the 16/17O isotope exchange on pure-anatase TiO2/A and mixed-phase TiO2/A + R with an anatase to rutile ratio of 1:1 has been performed. Evaluation of the exchange kinetics hints to a strong decrease of the activation energy of this reaction on mixed-phase TiO2/A + R material (61 (A) and 70 kJ/mol (R)) comp...

Phosphate‐modified ZSM‐5 zeolites were studied by standard characterization techniques and solid‐state nuclear magnetic resonance spectroscopy, and in the methanol‐to‐olefin (MTO) conversion. Considering the physicochemical properties of the ZSM‐5 zeolites, the most important effects of the phosphate modification are a deposition of polyphosphates...

'H magic angle spinning (MAS) NMR and FTIR spectroscopy with deuterated acetonitrile and pyridine as probe molecules, respectively, were used to study the strength of Brønsted acid sites in Pt- and lr-modified zeolites Y and Beta in comparison with the materials in their H,Na forms. For both types of zeolites, the following sequence of the acid str...

Formation of parahydrogen-induced polarization was investigated via hydrogenation of propene with parahydrogen on rhodium-modified zeolite Y (0.4[Rh]Na–Y) in the gas phase. The PASADENA (Parahydrogen and Synthesis Allow Dramatically Enhanced Nuclear Alignment) protocol was combined with in situ 1H MAS NMR under flow conditions for observing adsorbe...

1H and 27Al MAS NMR spectroscopies have been applied for studying the effect of water molecules, nitrogen bases, and o-xylene on the hydroxyl protons of bridging AlOH groups and framework aluminum atoms in the metal−organic framework (MOF) MIL-53. For water molecules adsorbed on the low-temperature form MIL-53lt, two 1H MAS NMR signals were found i...