Main research areas

Polyoxometalates (POMs) constitute a versatile class of molecules with a wide range of applications. In our research, we focus on harnessing their unique properties for catalytic processes, particularly for the valorisation of biomass and the development of sustainable chemical transformations.

POMs are anionic molecular clusters composed of transition metal ions (such as Mo^+VI or W^+VI) bridged by oxo ligands (O^2–). They exhibit a variety of structure types, broadly categorized into isopolyanions (containing only the metal and oxo ligands) and heteropolyanions (which additionally incorporate a heteroatom such as silicon or phosphorus). Both structure types can be further modified by partially substituting the framework metals with other transition metal ions (e.g., V^+V, Nb^+V, Co^+II, Ru^+III), allowing us to fine-tune their catalytic properties. Beyond structural variation and elemental substitution, the properties of POMs—particularly their solubility and reactivity—can also be controlled by carefully selecting their counterions.

Our team develops synthesis methods enabling us to specifically tailor POM characteristics—including structure type, composition, and counterion selection—to achieve desired molecular properties such as solubility, Brønsted versus Lewis acidity, and redox activity. Using these approaches, we create bespoke POM-based catalysts whose catalytic activity is systematically studied in diverse projects geared towards sustainable chemical processes.

Depending on the application, we use POMs either as homogeneous catalysts in solution or immobilized on support materials as heterogeneous catalysts. Through this research, we aim to exploit the full potential of POMs for innovative and sustainable chemical transformations.

Contact: Pegah Saedi (pegah.saedi"AT"uni-hamburg.de)

Supported Ru-X on carbon nanotubes as switchable catalyst for glycerol hydrogenolysis

The aim of CRC 1615: SMART-reactors is to build a reactor that converts renewable resources into different products (multipurpose) and that operates autonomously (self-adaptive). This will lead to more resilient processes that are better transferable between scales and locations. Designing tailor-made bi- or tri-metallic catalysts for the selective hydrogenolysis of glycerol, a major byproduct of biodiesel production, into 1,2-PD under mild reaction conditions is a key challenge for the project. Given that the catalyst's wettability should be switchable to make it more resilient against catalyst poisons, carbon nanotubes seem to be a promising support. To achieve this, we aim to develop a highly active and selective metallic catalyst on a tailor-made CNT-forest, whose wettability can be tailored by applying voltage.

Preliminary tests performed by our group showed that the combination of transition and noble metals is a promising approach. As ruthenium seems to be the best choice for the noble metal, finding the right transitional metal to complement the bi- or tri-metallic catalyst is a key step in our research. It is also important to find a suitable CNT support that further enhances catalytic activity. For that reason, we use different commercially available CNTs for the development of a powder catalyst. We want to find out if the properties crucial for catalysis in the tested powder CNTs are transferable to tailor-made CNT-forests from our project partners. It is also important to find the optimal metal ratio, loading, precursors, impregnation method, and conditions to develop the best possible catalyst. We test our catalysts in a multi-fold hydrogenation plant, which allows us to test our catalysts under different reaction conditions. This project is part of CRC 1615 SMART-reactors and is funded by the German Research Foundation (DFG) under the funding number 503850735. We work in close cooperation with our project partners from the working group of Prof. Dr.-Ing. Bodo Fiedler at the Institute of Polymers and Composites at TU Hamburg.

Contact:           samrin.shaikh@uni-hamburg.de  

                            dominique.lumpp@uni-hamburg.de

Polyoxometalates (POMs) are well-defined metal-oxyanions linked with oxygen bridges of early transition metals of the main groups 5 or 6 at their highest oxidation state. They can also contain a multitude of hetero anions like phosphate or silicate to improve their chemical and thermal stability. POMs have attracted considerable attention due to their fascinating architectures and attractive physico-chemical properties including strong Brønsted acidity, high proton mobility, fast multi-electron transfer, high solubility in polar solvents and resistance to hydrolytic and oxidative degradations. Many properties of POM materials can be tailored by changing the constituents and counter cations. Especially the enormous multifunctionality of POMs made them in particular attractive for various homogeneous catalysed applications.

However, homogeneous catalysis leads to several drawbacks like difficulties in catalyst separation and recycling as well as purification of the products. Furthermore, the low specific surface area of bulk POM-catalysts limits the field of application. Therefore, the development of heterogeneous POM-based catalysts with higher specific surface area has attracted much attention. Beside a better catalyst separation and catalyst recycling, especially extending the field of applications of POM-based materials to liquid-phase reactions in non-polar solvents and gas-phase reactions is one of the main goals.

There are several possibilities for heterogenisation of polyoxometalates:

• Impregnation on a porous support (via physical adsorption)
• Chemical immobilization via grafting on a porous support (covalent bondings using linker molecules)
• Complexation with organic or inorganic cations
• Encapsulation in highly porous frameworks

In our research group we are developing tailored heterogeneous POM-based materials using those heterogenisation methods for technical liquid phase and gas-phase applications.

We are working on this project together with our academic partners at Lyngby Technical University (DTU).

contact person: Maximilian Poller

Methanol Steam Reforming mit Indium-basierten Katalysatoren

UHH/Herrmann

Methanol is an excellent hydrogen carrier liquid, is easy to store and to transport without loss over long distances, and has a higher volumetric energy density than pure hydrogen. It has a high hydrogen to carbon ratio, lacks carbon-carbon bonds and can release hydrogen at mild conditions. In addition, methanol can already be transported using our current petroleum infrastructure. This allows energy to be transferred from areas with a lot of renewable energy to areas where a lot of hydrogen is needed and cannot be produced locally. This includes heavy industry and the energy needs of entire countries, being readily connected with ports and pipelines. Without, a lot of fossil fuels will still be needed to cover the energy demand of the latter.

The Methanol Steam Reforming (MSR) reaction is an important link to provide large amounts of hydrogen for energy and industrial processes. With adding steam to the reforming, the hydrogen bound in water can be released as well, increasing the overall hydrogen yield. In previous research, indium-based catalysts supported on zirconia have shown good results in the synthesis of green methanol using hydrogen and CO2 and may be suitable for the MSR reaction as well.

Different indium-based catalysst will be tested for their activity towards MSR in a dynamically operating fixed bed reactor. Subsequently, the catalyst will be tuned and the reaction conditions optimized, such as temperature, pressure, Steam/Methanol and more.

Contact: Nick Herrmann
Email: nick.herrmann"AT"uni-hamburg.de

SNISMs- Combined influence of pH, catalyst and strongly non-ideal solvent mixtures towards boosting acid-catalyzed reactions

The efficiency of chemical syntheses is determined by the interaction of catalyst and reaction medium. In homogeneous catalysis, high substrate solubility, fast kinetics, high yields and the recyclability of solvent and catalyst are desirable. As acid-catalyzed model reactions, esterifications of various organic acids (e.g. formic, acetic or lactic acid) with short-chain alcohols are investigated, using heteropolyacids (HPA) as catalysts, which are well known and used in the working group in a variety of applications.

Due to water formation during the reaction process, a reaction medium is required that keeps the thermodynamic water activity as low as possible, but at the same time maximizes the activity of the catalyst (proton activity) and the reactants in order to shift the thermodynamic equilibrium to the product side. When using a single solvent, often only one of these properties is achieved, e.g. reducing the water activity while also slowing down reaction kinetics. For this reason, solvent mixtures that deviate from Raoult's law due to strong interactions will be used in SNISMs. These can be, for example, organic solvents in combination with urea, terpenoids or sugars. The influence of SNISMs on the phase behavior, yield and reaction kinetics is not well known so far and will be investigated both experimentally and with a thermodynamic prediction tool.

This project is jointly carried out with the working group of PD Dr.-Ing. Christoph Held at the Chair of Thermodynamics at TU Dortmund University. Funded by the German Research Foundation (DFG) under the funding code AOBJ: 699314.

Contact: Lasse Prawitt (lasse.prawitt"AT"uni-hamburg.de)