Creating Novel Catalyst Materials with Unique Properties Is Now Possible

Generating new catalyst materials is crucial to optimize the production of the next generation of batteries and to improve the storage and conversion of energy. In order to ensure that sample preparation is more effective and make it a faster process, the Institute of Particle Technology TU Clausthal is using a new method to generate nanomaterials. In fact, with the spark ablation technique they are able to generate size-selected particles with unique material composition.

The Institute of Particle Technology at the Clausthal University of Technology focuses on all aspects related to particles in fluids with a special interest in nanoparticles in gases.

Their research includes fundamental study of interparticle cohesion in agglomerates and ways to influence the formation of such structures, the creation of novel catalyst materials with defined pore structures, the modification of particles with organic or inorganic coatings and new methods to measure certain particle surface properties.

Researchers at the Institute of Particle Technology at the Clausthal University of Technology.

Figure 1. Researchers at the Institute of Particle Technology at the Clausthal University of Technology.

For Which Applications Are Your Studies Relevant?

Most of our research is fundamental research, but we work on applications for catalysis, aerosol analysis and material modifications.

As an example, one project aims to produce a catalyst and support system optimized for the Fischer-Tropisch synthesis (a series of chemical reactions converting a combination of carbon monoxide and hydrogen into liquid hydrocarbons).

Fischer-Tropsch synthesis mechanism

Figure 2. Fischer-Tropsch synthesis mechanism

Another researches new ways to deoxidize particle surfaces to produce pure metal particles for the use in extremely high-vacuum laser beam melting processes. In a third, silica-like coatings are applied to different particles and can be used to control material properties such as the photocatalytic activity of titania, which can be relevant for sunscreens. The coatings can also be used to stabilize particle agglomerates against sintering or mechanical restructuring, which allows catalysts to retain a higher specific surface area. We also recently finished an industry project for the improvement of a device for the measurement of particles in exhaust fumes from small-scale heating systems.

Why Are You Using Nanoparticles as a Source?

Nanoparticles have many interesting properties that are not found in larger particles. This, as we know from molecules, results in the split-up of energy bands into individual energy states with decreasing particle size. This can be used to control the size of the band gap and hence, other properties defined by this, such as the wavelength of fluorescence radiation. The control of the band gap can be especially relevant for catalysts, such as the photocatalyst titania. Another important aspect of nanoscale particles is their much larger specific surface area compared to bulk materials. This is especially relevant for catalysts since the available surface area influences the reactivity significantly.

What Are the Most Common Difficulties in Generating Nanomaterials?

Many synthesis methods for nanoparticles use a form of chemical vapor deposition (CVD), such as the flame synthesis. The particles generated with these methods sometimes contain impurities from incomplete chemical reactions or adsorbed by products. Furthermore, these by-products can be hazardous (e.g., HCl) and need to be removed in additional process steps. In contrast, physical vapor deposition (PVD) techniques such as the spark discharge do not have these problems.

TEM micrograph of copper (Cu) nanoparticles produced by spark discharge

Figure 3. TEM micrograph of copper (Cu) nanoparticles produced by spark discharge

Why Do You Use Spark Ablation Technology?

The purely physical mechanisms resulting in the formation of particles without chemical reactions leads to pure aerosols that are ideal for the use as model particles for different studies. Furthermore, compared to other aerosol synthesis methods, the spark ablation and especially, the VSP-G1 nanoparticle generator, results in a stable and defined production even over longer time spans, which is important to draw meaningful conclusions.

Spark ablation technology

Figure 4. Spark ablation technology

For example, we use spark discharge produced metal particles as model particles in coating experiments, where we apply silica-like films on the particle surfaces in a post-discharge plasma process. The particles are mixed with a precursor, such as a tetraethoxysilane (TEOS), and the exhaust of a dielectric barrier discharge plasma reactor and then introduced into a coating chamber, where the coating formation takes place, resulting in so-called core-shell structures. Since the whole process is designed for the continuous coating of introduced aerosols, a stable source of nanoparticles is important; one that provides the particles without any by-products that might influence the coating formation and hence the conclusions of the work. A spark discharge generator can satisfy both requirements.

Researcher at TU Clausthal while using the VSPG1 nanoparticle generator

Figure 5. Researcher at TU Clausthal while using the VSPG1 nanoparticle generator

What Role Do You See for Aerosol Technology in the Development and Optimization of Catalysts?

An important aspect in heterogeneous catalysis is a high specific surface area of the active material, which is generally achieved using small particles. These particles are often deposited on a support material to stabilize them against sintering effects that become a problem for such small particles. However, the support often takes on an active role in the catalytic reactions due to interactions between it and the catalyst itself, which makes it hard to investigate only the reactions of the catalyst material.

In aerosol catalysis, the reactions take place on gas-borne nanoparticles that consist only of the catalyst without any support. This makes them ideal candidates for the study of specific catalyst properties such as the size, morphology or surface characteristics. Furthermore, aerosol catalysts are not as transport limited as supported catalysts, which provides easier experimental access to the reaction kinetics. Moreover, the short residence times of the aerosol catalysts in the system cause no significant changes in the reaction conditions and hence simplify the quantification of the catalytic activity. The spark ablation offers a good way to produce pure aerosol catalyst materials.

This information has been sourced, reviewed and adapted from materials provided by VSPARTICLE B.V.

For more information on this source, please visit VSPARTICLE B.V.

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