Research

Electrolysis converts electrical energy into chemical energy. Probably the most prominent example of this is the production of green hydrogen using wind and solar power.

Here at ITC, in addition to optimizing this low-emission process, we are motivated by the use of CO₂ as a feedstock for sustainable chemical production. Depending on the choice of catalyst, CO2 can be converted into various molecules. For example, tin and bismuth catalyze the reaction to form formic acid, iron to CO, or copper can be used to obtain C₂₊ products (e.g., C₂H₄, C₂H₅OH). To minimize mass transport problems in the three-phase reaction, so-called gas diffusion electrodes (GDE) are used. With the help of advanced techniques (e.g., EIS, in-situ XAS), the various catalyst systems can be characterized systematically and comprehensively.

Research here at ITC encompasses both small pilot plants (up to 3 A), detailed catalyst optimization, and proof-of-concept work. This involves addressing questions relating to suitable process parameters, cell design (e.g., zero-gap arrangement or choice of membrane), the composition of the GDE (homogeneous/inhomogeneous), and the catalyst layer (influence of the binder or ionomer, catalyst morphology, manufacturing processes such as electrodeposition or spray coating). In addition to this experimental approach, work is also being carried out on detailed modeling of the processes in the GDE. This two-pronged approach paves the way for a holistic understanding of the processes involved in the electrochemical reduction of CO₂.

Thermal catalysis plays a central role in converting chemical compounds through temperature driven reactions, enabling efficient energy and resource use in chemical processes. At the Institute for Technical Chemistry in Stuttgart, the research focuses on several key aspects of this field.

1. Catalyst Design aims to develop active and stable materials with tailored compositions and structures. By optimizing metal-support interactions and surface properties, catalysts can achieve higher selectivity and longer lifetimes even under harsh reaction conditions.
2. Kinetic Studies are providing quantitative insight into reaction rates and mechanisms. Systematic variation of temperature, gas composition and flow conditions help to identify rate-determining steps and allows the development of reliable kinetic models for reactor and process design.
3. Mechanistic Investigations combine experimental and modeling approaches to show how active sites function and how reaction intermediates form and transform.
4. Resistive Heating offers a different approach for strongly endothermic reactions, where conventional external heating often causes energy losses. By applying direct electrical heating to the catalyst, heat is generated exactly where it is needed, resulting in faster temperature control, higher energy efficiency and potentially lower CO₂ emissions.

In the ēQATOR project, these aspects are applied to the dry reforming of methane, converting methane and carbon dioxide into synthesis gas for the production of biomethanol. The project demonstrates how electrically heated catalytic systems can make high-temperature processes more efficient, flexible and sustainable.

In the research field of plasma catalysis, we investigate the potential of coupling electrically generated plasmas and heterogeneous catalysts for alternative processes for producing various chemical products. The unique physical properties of plasma as a partially to fully ionized gas, with a correspondingly high energy content and the occurrence of various excited states, open up new possibilities and reaction pathways.

The goal of plasma catalysis is to maintain specific excitation processes and then convert the respective species at the catalyst in order to achieve high conversion rates. At the Institute of Technical Chemistry, so-called DBD plasmas (dielectric barrier discharge) are being investigated. Here, an applied alternating voltage (kV range) causes discharges between two electrodes separated by a gas space and at least one dielectric. This arrangement allows a potential catalyst to be introduced directly into the plasma zone. Potential areas of application include both exothermic (e.g., ammonia production) and endothermic (e.g., dry reforming of methane) reactions.

The research questions here at the ITC relate to process and reactor design, catalyst design, and kinetic and mechanistic studies.

Microreaction technology deals with chemical reactions in continuous reactors with very small channel sizes (micro to millimeter range). These small dimensions enable rapid mixing of the reactants, effective heat transfer, and a narrow residence time distribution. This allows high selectivities and conversion rates to be achieved even in complex reactions. In addition, microreactors are particularly suitable for fast, highly exothermic, or otherwise safety-critical reactions.

In the research area of surface organometallic chemistry and molecular heterogeneous catalysis, well-defined active centers are synthesized on the surfaces of metal oxides. In the approach of surface organometallic chemistry, metal complexes are linked to the hydroxyl groups of the metal oxide surface via condensation or addition (A). In molecular heterogeneous catalysis, so-called anchor groups are attached to the backbone of a ligand of the metal complex, which serve as binding sites to the surface (B). The species synthesized in this way are analyzed using standard methods for investigating homogeneous and heterogeneous catalysts (IR, Raman, MAS NMR, X-ray diffraction, X-ray absorption, UV-VIS, XPS, TEM, SEM). We use these methods to investigate cycloenine isomerization, hydroformylation, ATR, Buchwald-Hartwig, and CO2-to-MeOH reactions.

Hydrogen spillover, the transfer of H₂ from a metal surface to a support (often metal oxides), is pivotal for many heterogeneous catalytic processes. In general, hydrogen spillover is mechanistically poorly understood, due to the H˙ donor complexity. Depending on certain parameters and properties regarding the metal oxide or used metal hydride, hydrogen spillover can proceed as a transfer of a hydrogen atom, a hydride or a proton. Decisive characteristics of the metal hydride include their acidity, bond dissociation free energy (BDFE) and oxidation potential, while properties of the metal oxide such as particle size, surface faceting, defects and vacancies influence the hydrogen spillover as well. The well-defined reduction using a metal hydride is considered a proton-electron transfer (PET) reaction, which creates new OH groups and reduced metal species on catalysts surface.

In the Estes Group at the University of Stuttgart, we use different metal hydride model compounds with various properties to enable the selective reduction of redox active metal oxides. Many of these metal oxides (CeO₂, V₂O₅, MoO₃, Bi₂O₃, MnO₂ and others) are used in a wide range of applications, including exhaust gas treatment, hydrodeoxygenation, electrochemical CO₂ reduction or oxygen evolution reaction (OER) and more. Ultimately, we aim to gain a deeper understanding in those catalyst systems. Comprehensively, this contains the synthesis and characterization of metal oxide materials as well as catalytic, kinetic and mechanistic studies.

Großtechnische Synthesewege zu CO₂-neutralen Aromaten und Olefinen sind rar. Ein Rohstoff, der bereits heute in erheblichen Mengen verfügbar ist, ist biobasiertes Ethanol. Ebenso wird aus Methan unterschiedlicher Herkunft Methanol in großen Mengen synthetisiert. Mit Hilfe von sauren Zeolithen werden beide Alkohole in eine Vielzahl von Olefinen und Aromaten umgewandelt. Dies macht Methanol und Ethanol zu perfekten Plattformen für die chemische Industrie von heute und morgen. Unser Ziel ist es, verbesserte Katalysatoren für die Umwandlung zu finden und ein tieferes Verständnis des Reaktionsmechanismus zu erlangen.

The crucial properties of functional solids are determined by the number and identity of their active sites. However, before these sites can participate in a chemical reaction, access to them by molecules must be ensured. Particularly in solids, far fewer sites are typically accessible than the total number of sites present, with significant implications for catalytic applications.

The preferred method for investigating the number of accessible functional sites is the use of so-called "probe molecules" and the analysis of the resulting surface species using spectroscopy. Our goal is to develop novel methods that enable a deeper understanding of solid-state functionalities.