Whether for cling film or hydrogen production, in chemistry, everything strives for efficient, inexpensive catalysts. Yet surprisingly, little is known about how they work on a molecular level. Prof. Murielle Delley from the University of Basel aims to change this and is developing methods to promote the production of more efficient, sustainable catalysts. She has now been awarded the 2024 Ruzicka Prize for her work on the controlled surface modification of cobalt phosphide with sulfur.
Do you know "Where's Waldo"? In this famous book series, one will find a picture of a busy ski slope, and hidden among all the skiers is a gentleman called Waldo. The goal is to find him. Murielle Delley is also on the lookout for him: privately, when she is leafing through the book with her children, but also professionally in a metaphorical sense.
The assistant professor at the Department of Chemistry at the University of Basel likes to compare the ski slope picture in her lecture with the surface of a heterogeneous catalyst - a solid substance that can enable and accelerate reactions without being consumed. "The busy ski slope is intended to illustrate the complexity of the chemistry on such catalyst surfaces because many things happen simultaneously there, too," Murielle Delley explains.
The skiers represent different catalytically active centers ("sites") - places that interact with the reactant. Some people ski purposefully downhill, so are catalytically active in chemical terms, while others sit in the chairlift (they are "inactive"), and still others pursue other activities (side reactions). "In this chaos, it is quite challenging to find and investigate the site that is particularly relevant for catalysis. Metaphorically speaking, this site would be our Waldo," the chemist explains.
Delley's research focuses on how catalysts function chemically, how to control their function, and how catalysts for certain processes - e.g. for electrolysis in hydrogen production - can be produced more specifically. Although it is already possible to observe how a material or surface behaves, enormous gaps in our knowledge at the molecular level still remain. Murielle Delley recently took the first major steps towards closing this gap by developing tools to understand the behaviour of a new class of materials in catalysis.
Noble is good, earth-abundant is better
It is no secret that chemical production always strives for efficient, cost-effective processes. Catalysts play an important role in this. "However, many are not understood well enough and contain materials that are not sustainable," Delley explains.
Due to their properties, platinum or palladium often have been the catalyst of choice, but they are expensive precious metals that are scarcely available. Other transition metals are now being considered as an alternative, often in combination with phosphorus. Among these so-called transition metal phosphides, cobalt phosphide (CoP) has emerged as a promising substitute for noble metals in many important industrial reactions.
"CoP is much more common than noble metals, but has similar catalytic properties, for example in hydrogenation - very important reactions in the production of many chemical products," Delley explains. CoP can also be synthesized easily and in a controlled manner. This was one of the reasons why she thought it would be a good model system for research into surface chemistry.
Delley has been working in this field since 2017. Before that, the enthusiastic student with roots in Fribourg studied chemistry at ETH Zurich. Delley always felt at home in science and was interested in fundamental processes with practical applications. During her doctorate supervised by Prof. Christophe Copéret at ETH Zurich, she researched chromium-based, heterogeneous catalysts, which are of great importance in producing polyethylene. Delley's award-winning doctoral thesis (Delley 2017) contributed to a better understanding of these catalysts.
New perspectives for catalytic design
Later, as a professor, Murielle Delley noticed that sulfur plays a major role in transition metal phosphide-based catalysts in the field of electrocatalysis and hydrotreating, but its specific function was barely understood. "That's why we started producing cobalt phosphides, CoP for short, and attached sulfur to its surface using molecular methods." Then the sulfur was quantified and analyzed using NMR and surface-sensitive spectroscopy.
Delley's group has used various phosphine sulfides for sulfur transfer. These phosphine sulfides differ in their properties and can add different amounts of sulfur to the surface. "As a result, we obtained various cobalt phosphides with different amounts of sulfur, bound with varied strength to the surface- in other words, a series of catalysts that we were able to test for catalysis," explains Delley. "Because we work with equilibrium reactions, we were able to infer the thermochemical properties of sulfur at the surface, which in turn shed light on the function of sulfur in these catalytic reactions" ( Arnosti et al. 2023 ). This opens new avenues for catalyst design.
"Research like this can only be achieved through teamwork. The materials remain complex even in the test setting, which means we have a relatively large experimental variation from experiment to experiment. Many repetitions with the same parameters were necessary to balance this out statistically. This is just possible with an excellent team," Delley emphasizes.
For her chemical modification of catalytic surfaces Murielle Delley has now been awarded the 2024 Ruzicka Prize.
"Being awarded the Ruzicka Prize is a huge honor for me and my group, especially as it means that we join the ranks of many other outstanding Ruzicka Prize winners."Prof. Murielle Delley (Photo: Karissa Van Tassel)
The prize may also be an incentive for further projects. After all, chemical modification is only one branch of Murielle Delley's research. Her second area of interest deals with the physical aspects of the catalyst surface - a topic that Delley got interested in during her postdoctoral years at Yale. Now that her group is growing, she also aims to "investigate electric fields as control element in thermal reactions" and hopes to publish exciting results in this area soon.
Until then, she will be doing what she loves best in her job - discussing scientific ideas with people - while in her private life, she will be exploring the great outdoors with her family, perhaps even hitting some ski slopes.
Murielle Delley Murielle Delley studied chemistry at ETH Zurich and completed her PhD with Professor Christophe Copéret in 2017. For her PhD thesis "Molecular-Level Understanding of Structure and Reactivity of Isolated Chromium Sites on Oxide Surfaces", Murielle Delley received the Prix Schlaefli 2019 in Chemistry by the Swiss Academy of Sciences. After a postdoc at Yale University with Professor James M. Mayer, Murielle Delley started her career at the Department of Chemistry at the University of Basel (Branco Weiss fellow, PRIMA professor of the Swiss National Science Foundation). In 2023, she started her tenure-track assistant professorship at the University of Basel.
