Producing hydrogen from renewable energy sources such as solar energy is the missing link in the process of long-term energy storage and environment-friendly hydrogen vehicles. Heterogeneous catalysis can make this possible.

Heterogeneous catalysis is an interfacial phenomena, and consequently requires a high surface area to be efficient. Nanocatalysts have a very high surface/volume ratio due to their size, which means a high activity with a low amount of material. However once they are dispersed in a large reactor, controlling and recovering these nanocatalysts is extremely challenging. Nanocatalysts are usually embedded into porous materials that do not interfere with the chemical reactions. This matrix must have small pores to offer a large contact area between the nanocatalysts and the media, and pores large enough to enable a good transport of the reactants and the products. These two conditions can be fulfilled if the matrix presents a hierarchy of pore sizes.

We synthesize porous microbeads (100 µm) loaded with nanocatalysts (20 nm) and which presents different sizes of pore (about 1 µm). We use microfluidics to have a good control of the physical conditions and therefore of the pore formation. In our microfluidic chip, we create nanocatalysts-loaded droplets that are cooled down along their trajectory in the channels. When temperature drops, the components of the droplets demix and we use UV light to solidify one of the two phases of the droplets. When the second phase is rinsed we obtain porous microbeads. The alignment of the temperature gradient with the UV beam is our lever to tune the properties of our system of pores. We will then measure the catalytic activity of our beads and optimize it by adjusting the size of the pores that depends on the alignment of the UV beam.

Left: Three steps of microbeads production: initial homogeneous and hot droplet laoded with nanocatalysts, cold and demixing droplet, porous microbeads after solidification of the red phase and rinsing of the blue phase. Right: Scanning-electron-microscopy image of our material loaded with nanoparticles prepared in a vial (scale bar 2 µm).

Our first target application is ethanol reforming to produce hydrogen under illumination with sun or UV light. Several nanocatalyst are known to make this reaction possible such as platinum-titania nanoparticles. However our aim is to produce a versatile matrix so we will later use these microbeads with other kind of nanocatalysts to prove their versatility.

Project leader: Prof. Albert van den Berg

Fine control over placement of materials on the nano- and meso-scale is a key element of designing new materials. In this project we aim to shed new light on one way to control the structure of these materials over multiple length scales: hierarchical self-assembly. In hierarchical self-assembly, we start by arranging atoms into clusters, which are often called nanoparticles. Then, the nanoparticles can be organized into larger clusters, and this process continues on different length scales with new properties and functionalities added at each self-assembly step. The structural properties of the resulting material are determined by the shape, size, and materials used in each assembly step. Recently the soft condensed matter group at UU investigated in experiments and simulations the self-assembly (SA) of nanoparticles inside the confinement of slowly drying emulsion droplets. They showed that the spherical confinement influences the SA process in an intriguing way, leading to crystalline clusters (supraparticles) with icosahedral symmetry. In this project, we will use computer simulations to provide support to optimize the structure of these supraparticles by tuning the shape and interactions of the nanoparticles, and to understand all aspects, including the effect of hydrodynamics, on the SA of particles in emulsions.

Project leader: Prof. Marjolein Dijkstra

The Soft Condensed Matter group at UU was among the first to investigate both in experiments and simulations the self-assembly (SA) of nanoparticles (NPs) inside the confinement of slowly drying liquid emulsion droplets. The resulting colloidal crystalline ‘supraparticles’ (SPs) have sizes still in the colloidal domain, so that another SA step is possible. It was found that the spherical confinement influences the SA process in intriguing and important ways compared to bulk SA. Here we want to use the experience obtained and optimize binary and single (rod-like) NPs brought into SPs for photo-catalysis using high-index NPs specifically designed/optimized for water splitting as proof of principle. We want to make use of Mie resonances of the resulting SPs to locally enhance light fields strongly. We will also explore using E-fields in still liquid SP systems and to tune the shape of the SPs. Also in this project we will develop/explore/optimize a microfluidics approach to make SPs on a gram scale.

Project leader: Prof. Alfons van Blaaderen

 

Recent studies indicate that heterogeneous catalysts vary tremendously, induced by dynamic changes in the active sites due to gradients in reaction conditions over the catalyst bed, both between and within single particles. Traditional characterization of catalyst particles in large vessels results in measurements representing ensemble averages. On the other hand, individual particle characterization is costly and time consuming and can therefore only be done on a limited amount of particles. There is a need for a single catalyst diagnostic platform for on-line evaluation of the catalytic performance of individual catalyst particles, to increase fundamental understanding of the catalytic conversion process.

One of the routes to assess the behavior of single catalyst particles is by making use of impedance spectroscopy. With impedance spectroscopy, the imaginary and real part of the impedance can be recorded as a function of the frequency of the signal, applied to two conducting electrodes, e.g., manufactured in a microfluidic channel. It is the final aim of this project to come to an optimal catalytic performance via a profound understanding of the catalytic chemical reaction.

Project leader: Prof. Albert van den Berg

Recent studies indicate that heterogeneous catalysts vary tremendously, induced by dynamic changes in active sites both between and within single catalyst particles. Traditional characterization approaches of catalyst particles in large reactor vessels results in measurements representing ensemble averages. On the other hand, individual particle characterization is costly and time consuming and can therefore only be done on a limited amount of catalyst particles. There is a need for a single catalyst diagnostic platform to characterize single particles at low-cost and high-throughput, to enable a massive search to find and select the best catalyst particles and related synthesis formulation approaches. Droplet microfluidics can trap single catalyst particles at several thousands of droplets per second, and allows to graft, react, and analyse each particle individually. The most promising particles can be selected for further in-depth analysis. Ultimately, the knowledge obtained from this research project will help to improve catalyst particles for use in fluid catalytic cracking (FCC) in the areas of the petrochemical industry and biomass conversion.

Project leader: Prof. Albert van den Berg

We propose to detect in-situ soft x-ray microscopy with a novel nanoreactor design based on 2D detection of the x-ray absorption/scattering/emission signal, where along a line through the sample the x-ray emission spectrum is instantly measured at every pixel. The enhancement of the nanoreactor robustness in combination with the improved detection options will allow a range of operando catalytic experiments in the fields of Fischer-Tropsch synthesis, carbon dioxide activation and biomass conversion. The novel design will also allow us to incorporate inline reactant/reaction product sensing with optical methods, such as SERS, or mass spectrometry, to make the direct connection between the state of the catalyst material and its catalytic performances.

Project leader: Prof. Frank de Groot

Aqueous phase reforming (APR) is an appealing process to produce hydrogen from widely available resources. In this project, the process of APR is implemented in a dedicated microfluidic reactor, using  dedicated metal-based catalysts which are immobilised on a solid support.

Project leader: Dr. Severine Le Gac