Uta Hejral studies catalysts for a sustainable future

A mass of wires, bolts, steel bars, and chrome – the vacuum chamber standing in a lab at the Physics’ Research Building makes an intriguing impression with all its various details, and at first glance, it is not entirely easy to understand how it works. Its purpose is to achieve an extremely low pressure, which is essential for certain types of research.

That is why researcher Uta Hejral prepares catalyst material samples using the ultra-high vacuum pressure in the chamber. The instrument is a crucial part of the laboratory she has been building since starting as an Assistant Professor at Chalmers in the autumn of 2023, having acquired it from a professor at Linköping University.

The use of such instruments was popular during the 1990s and 2000s, when the study of well-defined systems under controlled conditions was at its hayday. However, this type of research was gradually abandoned in favour of studies of industrial samples under industrial conditions. Uta Hejral and her team combine both worlds: they prepare well-defined material systems under vacuum conditions, but they investigate them under realistic harsh industrial conditions.

"When I started at Chalmers and said that I needed such instruments for my research, I was told, unfortunately, we used to have them, but they had been given away," Uta Hejral says, laughing.

Now, however, a vacuum lab is taking shape once again. Here, Uta Hejral's research group will grow nanoparticles for model catalysts – simplified versions of industrially used catalysts – under ultra-high vacuum with extremely low pressure. The instrument can reach 10^-14 bar (i.e. 0.000 000 000 000 01 bar), and at that level, the nanoparticles can begin to grow in a defined way. In addition, the setup hosts equipment that will facilitate to obtain information on the composition and the structure of the grown nanoparticles at the atomic-scale, the team will actually be able to see individual atoms.

Studying how to improve catalyst efficiency

Catalysts are used to accelerate a reaction without being consumed themselves. They are indispensable in industrial processes and are used in everything from the food industry and petrochemicals to pharmaceutical production.

"When I started researching this field, I was amazed at how much actually depends on catalysts. At some point in the production chain of almost every product we use in everyday life, a catalyst has been involved. Without them, large parts of our modern industry would not function – they essentially keep the world turning. Catalysts are used everywhere – in fuel cells, the chemical industry, electrolysers, and automotive catalytic converters," says Uta Hejral.

"To improve a catalyst's efficiency, one must understand what happens at the atomic level, what structure is present when the reaction occurs. This happens in real-time under harsh conditions. Since we prepare the samples under strictly controlled conditions in the lab, we know exactly what they look like. This allows us to study specific aspects, such as what happens on a particular crystal surface or how the structure changes during a reaction. Industrial catalysts consist of randomly distributed nanoparticles, and certain details are impossible to study on such complex samples while the reaction is taking place. Therefore, we use model systems that enable us to see what is happening."

Investigating samples at synchrotron facilities

Once prepared, Uta Hejral then takes the samples to state-of-the-art synchrotron facilities, such as MAX IV or Petra III at DESY , to study them under realistic conditions. Using X-ray diffraction, she can track how particle shapes change and whether certain nanoparticle facets form a 2D oxide layer with a thickness of only three atoms while other facets remain metallic – something that cannot be observed in industrial catalysts.

The long-term goal of her research is to develop new catalysts made from materials that are abundant, such as nickel, cobalt, and iron, instead of the expensive precious metals currently in use.

"In industry, large amounts of energy are required to drive reactions. If we can improve efficiency by just one percent, it would result in enormous energy savings, which would be highly beneficial for a sustainable climate transition. Additionally, we want to find new material systems that are more accessible and sustainable."

Growing nanoparticles sparked her interest

Already during her school years in her home country of Germany, Uta Hejral was drawn to natural sciences, especially physics, first with a particular interest for astronomy. She began studying physics combined with English literature and linguistics in Stuttgart, Germany, and in Kingston, Canada. During her diploma work at the Max Planck Institute for Metals Research in Stuttgart, her fascination started drifting towards synchrotrons instead.

"When it was time for my diploma thesis, I knew I wanted to work with synchrotrons. That was actually how I got into the field of catalysis. I started growing platinum nanoparticles and realised that I really enjoyed seeing how they behave in X-ray diffraction and how their properties change depending on the surrounding gas composition."

Exploring catalytic reactions relevant to climate change

Today, Uta Hejral’s research group investigates mainly catalytic reactions that are important for the decarbonization of the society. These include the conversion of greenhouse gases carbon dioxide into value-added products such as the fuel methanol, as well as the production of molecular energy carriers such as green hydrogen through water splitting with the goal to chemically store the energy from solar and wind power, thereby compensating for energy production downtimes.

"We believe that we can improve the catalyst efficiency of the water splitting reaction. We have an electrochemical cell that we use at synchrotrons to study water splitting, and we will also be able to use it in the lab once everything is in place. Additionally, we will have a high-pressure cell for gas-phase catalysis, where we can investigate methane activation and carbon dioxide hydrogenation at very high pressures, up to 100 bar. This is the project of one of my PhD students who has just started recently. Many catalytic reactions occur under such conditions, so this will be an important part of our research."

"Right now, we are studying what a catalyst's structure looks like when it is most active. We also study alloys, i.e. materials that consist of more than one chemical element, with the aim to improve the catalytic activity. One of my PhD students is working on iron-doped nickel, and my postdoc is working on iron-doped cobalt. We see clear improvements, but the exact mechanism is not yet fully understood. In the long run, our research may enable the use of more sustainable and accessible catalysts on an industrial scale."

A commitment to sustainability

The common denominator in Uta’s various research projects is that they all contribute to the green transition. For her, dedicating her work to this cause is a given.

"Climate change is the greatest crisis humanity faces, so being able to contribute to sustainability in even the smallest way feels absolutely necessary," says Uta.

"When conducting research, it can take a long time before things fall into place, and you get the result you want. Perseverance is required daily. You are paving the way where no one has gone before, and sometimes taking a wrong turn is completely normal. The important thing is to remain optimistic and believe that it will work out, trust the process. Once in a while you obtain unprecedented and unexpected results that push your research field further, and when that happens, it is incredibly exciting!"

About Uta Hejral:

• Before coming to Chalmers in the autumn of 2023, Uta Hejral was a postdoc at the Fritz Haber Institute in Berlin, Germany, and at Lund University, Sweden.
• She is a fellow in the WISE programme, the Wallenberg Initiative Materials Science for Sustainability, which aims to enable sustainable technologies with a positive impact on society by understanding, creating, and controlling complex materials.
• Uta Hejral’s research group includes postdoc Fanny Duquet and the PhD students Felix Simon and Roberto Dore. In addition, the group greatly benefits from the expertise of senior lecturer Lars Hellberg on ultra-high vacuum equipment, he helps setting up the lab.

Uta Hejral on…

… growing nanoparticles on samples that are five nanometres large (a DNA strand, by comparison, is about 2.5 nanometres in diameter): "It’s a slow process. As the material evaporates and atoms stick to the surface, you simultaneously heat the substrate so that the atoms can move and find each other. That’s when the particles slowly start to grow. Without that time, you would just get an undefined layer of material. Growing a sample can take up to five hours or even more, despite the particles being so small."

… encountering dead ends as a researcher: "Research is about doing something new and walking a path no one has taken before. Running into dead ends is normal. It took me a while to realise that. Early in my research career, I thought it was just me facing problems, but then I understood it’s part of the process."

… working in academia: "One reason I wanted to stay in academia is the international environment. You meet people from all over the world and learn new things almost every day. It’s a very diverse job – one day you’re working hands-on in the lab, the next you’re analysing data, writing articles, or giving presentations. Travelling to synchrotrons for experiments is also part of the job. It never gets boring!"