POSTMODERN ALCHEMY

Simulations and experiments meet: Machine learning predicts the structures of gold nanoclusters

University of Jyväskylä - Jyväskylän yliopisto

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Atomistic snapshots describing how two thiolate-protected gold nanoclusters of 144 gold atoms each coalesce producing a single larger cluster matching a size that previously has been synthesized. 

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Credit: Maryam Sabooni Asre Hazer, University of Jyväskylä.

Researchers at University of Jyväskylä (Finland) advance understanding of gold nanocluster behavior at elevated temperatures using machine learning-based simulations. This information is crucial in the design of nanomaterials so that their properties can be modified for use in catalysis and other technological applications.

Thiolate protected gold nanoclusters are hybrid nanomaterials with promising applications in nanomedicine, bioimaging and catalysis. However, understanding how these nanoclusters behave under elevated temperatures, which is critical for their use, has remained largely unexplored due to the prohibitive computational cost of traditional simulation methods. 

Record-long simulations of gold nanoclusters

Researchers at the University of Jyväskylä have successfully employed machine learning-driven simulations to investigate the thermal dynamics of Au₁₄₄(SR)₆₀, one of the most well-studied gold nanoclusters. Using a recently developed atomic cluster expansion (ACE) potential trained on extensive density functional theory data, the researchers conducted molecular dynamics simulations extending up to 0.12 microseconds. This is approximately five orders of magnitude longer than what is feasible with conventional quantum chemical methods.

"This work opens new possibilities for understanding how ligand-protected metal nanoclusters behave under realistic operating conditions," says lead author Dr. Maryam Sabooni Asre Hazer. "Through this work, we can observe in atomistic detail how these clusters transform, fragment, and even merge at elevated temperatures over timescales that are relevant for experimental conditions."

Layer-by-layer thermal transformations revealed

The study revealed that thermal effects induce structural changes in a layer-by-layer fashion, starting from the outermost gold-thiolate protective shell. At temperatures between 300 and 550 K, the researchers observed the spontaneous formation of polymer-like chains and ring structures of gold-thiolate units, which can dynamically detach and reattach to the cluster surface. The remaining cluster compositions closely matched those observed in experimental studies, demonstrating the accuracy of the machine learning potential.

"What's particularly exciting is that we can now see how gold atoms migrate between different layers of the cluster and how the surface restructures under thermal stress," explains Dr. Sabooni Asre Hazer. "These processes are directly relevant to understanding why thermally treated gold nanoclusters become effective catalysts."

Gold clusters joined together in the simulation

In an even more remarkable finding, the researchers successfully simulated the complete coalescence of two Au₁₄₄(SR)₆₀ clusters at 550 K. The fusion process produced a larger cluster with composition Au₂₃₉(SR)₆₉, strikingly similar to a gold nanocluster previously synthesized experimentally. 

"The merged cluster exhibited a twinned face-centered cubic metal core structure, matching the symmetry determined from experimental X-ray diffraction data," says Dr. Sabooni Asre Hazer.

Opening new avenues for nanomaterials research

The methodology enables detailed atomistic studies of processes that were previously inaccessible to computational investigation, including cluster-cluster interactions, catalytic activation mechanisms, thermal stability, and inter-particle reactions.

"Our results provide fundamental insights into how ligand-protected nanoclusters behave as they transition toward larger nanoparticles," explains Professor Hannu Häkkinen, who supervised the research. "This knowledge is instrumental for the rational design of nanomaterials with tailored functionalities for catalysis and other applications.", he continues. 

The research was published in Nature Communications. The publication was recognized as an Editors' Highlight in the Inorganic and Physical Chemistry section of Nature Communications.

The work was supported by the Research Council of Finland and the European Research Council (ERC) through the Advanced Grant project DYNANOINT. Computational resources on supercomputers Puhti and Mahti were provided by the Finnish national supercomputing center CSC. 

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Journal

Nature Communications

DOI

10.1038/s41467-025-67700-w 

Method of Research

Imaging analysis

Subject of Research

Not applicable

Article Title

Thermal dynamics and coalescence of Au144(SR)60 clusters from a machine-learned potential

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21st CENTURY ALCHEMY

Sulfur isn’t poisonous when it synergistically acts with phosphine in olefins hydroformylation

Dalian Institute of Chemical Physics, Chinese Academy Sciences

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Researchers at the Dalian Institute of Chemical Physics have designed a rhodium catalyst whose microenvironment is tuned by both sulfur and phosphine ligands, based on an industrial single-site Rh1/POPs catalyst. The new “single-site” catalyst hydroformylates propylene and higher olefins up to twice as fast as the current benchmark, while maintaining high selectivity and stability. The study explains how a carefully controlled amount of sulfur can switch from poisoning the catalyst to promoting its performance.

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Credit: Chinese Journal of Catalysis

Dalian, China-Sulfur, long feared as a “poison” that shuts down precious metal catalysts, can actually help them work better when used in just the right way, according to new research published in Chinese Journal of Catalysis.

A team led by Prof. Yunjie Ding at Dalian Institute of Chemical Physics, Chinese Academy of Sciences andProf. Xueqing Gong at Shanghai Jiao Tong University, has shown that a tiny, carefully tuned amount of sulfur can boost the speed and robustness of a key industrial reaction by up to twofold.

The reaction, called hydroformylation, adds carbon monoxide and hydrogen to simple molecules known as olefins (alkenes) to make aldehydes. These aldehydes are essential building blocks for alcohols, plasticizers, surfactants, lubricants and many other bulk and specialty chemicals. Worldwide, more than 25 million tons of aldehydes and alcohols are made each year by hydroformylation, mostly using rhodium-based catalysts dissolved in liquid.

“Hydroformylation is one of the workhorses of modern chemical industry,” the authors note in the paper. “Designing catalysts that are both highly active and tolerant to real-world, sulfur-containing feedstocks is crucial for greener production.”

Traditionally, sulfur compounds in feed gases or liquids are seen as a serious problem. They bind very strongly to precious metals like rhodium, blocking the active sites and deactivating the catalyst. As a result, major effort is spent on deep desulfurization-removing sulfur as completely as possible before the reaction.

The new study takes a very different approach: instead of fighting sulfur at all costs, the researchers ask whether sulfur can be harnessed and controlled.

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Tuning the catalyst’s “microenvironment”

The team builds on an earlier heterogeneous (“solid”) rhodium catalyst, known as Rh₁/POPs-PPh₃, in which isolated rhodium atoms are anchored to a porous organic polymer (POPs-PPh3) through frame-phosphine (frame-P) ligands. That system has already been demonstrated at industrial scale for hydroformylation.

In the new work, the researchers designed a related material where the porous polymer framework contains both phosphine and sulfur sites. When rhodium is introduced, each single rhodium center can be coordinated by a mixture of phosphorus and sulfur atoms, creating a sulfur–phosphine co-coordinated microenvironment (Rh₁/POPs-PPh₃&S).

By varying the ratio of sulfur to phosphine in the polymer, they discovered a “sweet spot”:

• At about 10% sulfur in the framework, the new catalyst hydroformylates propylene and C₅–C₈ olefins 1.5–2.0 times faster than the phosphine-only benchmark,
• while maintaining high selectivity to the desired linear aldehydes and showing excellent stability in long-term tests.

In contrast, when sulfur dominates the coordination, the catalyst indeed suffers severe sulfur poisoning and its performance drops sharply, confirming that dosage and microenvironment are critical.

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Seeing how sulfur helps instead of “hurts”

To understand why a small amount of sulfur promotes rather than harms, the team combined advanced characterization and computer modelling.

Using high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and X-ray absorption spectroscopy, they confirmed that rhodium remains atomically dispersed — as single “mononuclear” centers — in both the original and the sulfur-modified catalysts. Solid-state NMR and X-ray photoelectron spectroscopy showed that adding sulfur partly replaces phosphine around rhodium slightly lowers the electron density on the metal.

In simple terms:

• Phosphine ligands are strong electron donors. They tend to make rhodium more electron-rich and highly reactive.
• Sulfur ligands are more electron-withdrawing and occupy one coordination site, which can moderate rhodium’s reactivity.

Using in-situ infrared spectroscopy under reaction conditions and temperature-programmed surface reaction experiments, the researchers observed that the sulfur–phosphine catalyst forms key aldehyde-forming intermediates faster, while suppressing unwanted hydrogenation and isomerization by-products.

Density functional theory (DFT) calculations then revealed that the rate-determining step in hydroformylation — the insertion of the olefin into a rhodium–hydrogen bond — has a lower energy barrier on the sulfur–phosphine co-coordinated catalyst than on the phosphine-only one. The calculations also showed how the combination of electron-donating phosphine and electron-withdrawing sulfur tunes the charge and bond lengths around rhodium into an optimal window for reactivity and selectivity.

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Rethinking “sulfur poison” for real-world feedstocks

The work provides a unified picture of when sulfur behaves as a poison and when it can act as a promoter:

• Too little sulfur, and the catalyst behaves like the original phosphine system.
• Too much sulfur, and rhodium sites are blocked, leading to classic sulfur poisoning and poor performance.
• At an intermediate sulfur level, the microenvironment around single rhodium atoms is ideally tuned, giving higher activity, better regioselectivity and robust stability.

This insight could be particularly important for processing sulfur-containing feedstocks, such as coal-based chemicals, biomass-derived oils, or low-grade olefin streams, where completely removing sulfur is costly or impractical.

“Our results suggest that, instead of treating sulfur as an absolute enemy, we can sometimes design catalysts that tolerate and even use sulfur to their advantage,” the authors write. The concept of microenvironment engineering around single-atom active sites may also be applied to other catalytic reactions beyond hydroformylation.

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Article details

The research article, “Regulating microenvironment of heterogeneous Rh mononuclear complex via sulfur-phosphine co-coordination to enhance the performance of hydroformylation of olefins,” by Siquan Feng, Cunyao Li, Yuxuan Zhou, Xiangen Song, Yunjie Ding and co-workers, appears in Chinese Journal of Catalysis (Vol. 78, 2025, pp. 156–169).
DOI: 10.1016/S1872-2067(25)64795-4

Corresponding authors:

• Prof. Yunjie Ding, Dalian Institute of Chemical Physics, Chinese Academy of Sciences
  Email: dyj@dicp.ac.cn

About the Journal

Chinese Journal of Catalysis is co-sponsored by Dalian Institute of Chemical Physics, Chinese Academy of Sciences and Chinese Chemical Society, and it is currently published by Elsevier group. This monthly journal publishes in English timely contributions of original and rigorously reviewed manuscripts covering all areas of catalysis. The journal publishes Reviews, Accounts, Communications, Articles, Highlights, Perspectives, and Viewpoints of highly scientific values that help understanding and defining of new concepts in both fundamental issues and practical applications of catalysis. Chinese Journal of Catalysis ranks among the top one journals in Applied Chemistry with a current SCI impact factor of 17.7. The Editors-in-Chief are Profs. Can Li and Tao Zhang.

At Elsevier http://www.journals.elsevier.com/chinese-journal-of-catalysis

Manuscript submission https://mc03.manuscriptcentral.com/cjcatal

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Journal

Chinese Journal of Catalysis

DOI

10.1016/S1872-2067(25)64795-4 

Article Title

Regulating microenvironment of heterogeneous Rh mononuclear complex via sulfur-phosphine co-coordination to enhance the performance of hydroformylation of olefins

21ST CENTURY ALCHEMY

A platform of gold reveals the forces of nature’s invisible glue

Chalmers University of Technology

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Researchers at Chalmers University of Technology, Sweden, have discovered a quick and easy way to study the hidden forces that bind the smallest objects in the universe together. Using gold, salt water and light, they have created a platform on which the forces can be seen through colours. Two thin glass plates hold everything needed to study nature’s invisible glue.

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Credit: Chalmers University of Technology | Mia Halleröd Palmgren

When dust sticks to a surface or a lizard sits on a ceiling, it is due to ‘nature’s invisible glue’. Researchers at Chalmers University of Technology, Sweden, have now discovered a quick and easy way to study the hidden forces that bind the smallest objects in the universe together. Using gold, salt water and light, they have created a platform on which the forces can be seen through colours.  

In the lab at Chalmers, doctoral student Michaela Hošková shows a glass container filled with millions of micrometre-sized gold flakes in a salt solution. Using a pipette, she picks up a drop of the solution and places it on a gold-coated glass plate in an optical microscope. What happens is that the gold flakes in the salt solution are immediately attracted to the substrate but leave nanometre-sized optical spaces between them and the gold substrate. The cavities created in the liquid act as resonators in which light bounces back and forth, displaying colours.  When the microscope’s halogen lamp illuminates the platform and a spectrometer separates the wavelengths, the different colours of light can be identified. On the monitor which is connected to the lab equipment, it is now possible to see many flakes moving and changing to colours like red and green against the golden yellow background. 

Studying ‘nature’s glue’ using light trapped in tiny cavities

“What we are seeing is how fundamental forces in nature interact with each other. Through these tiny cavities, we can now measure and study the forces we call ‘nature’s glue’ – what binds objects together at the smallest scales. We don’t need to intervene in what is happening, we just observe the natural movements of the flakes,” says Michaela Hošková, a doctoral student at the Department of Physics at Chalmers University of Technology and first author of the scientific article in the journal PNAS in which the platform is presented.

Through the light captured in the cavities, the researchers can study the delicate balance between two forces – one pulling the tiny objects towards each other and one holding them apart. The joining force, the Casimir effect, makes the gold flakes connect to each other and the substrate. The second, electrostatic force, arises in the salt solution and prevents the flakes from sticking completely to the substrate. When those two forces balance each other, this is known as a self-assembly process and the result is the cavities that open up new research possibilities.

“Forces at the nanoscale affect how different materials or structures are assembled, but we still do not fully understand all the principles that govern this complex self-assembly. If we fully understood them, we could learn to control self-assembly at the nanoscale. At the same time, we can gain insights into how the same principles govern nature on much larger scales, even how galaxies form,” says Michaela Hošková. 

Gold flakes become floating sensors

The Chalmers researchers’ new platform is a further development of several years of work in Professor Timur Shegai’s research group at the Department of Physics. From the discovery four years ago that a pair of gold flakes creates a self-assembled resonator, researchers have now developed a method to study various fundamental forces.

The researchers believe that the platform, in which the self-assembled gold flakes act as floating sensors, could be useful in many different scientific fields such as physics, chemistry and materials science.

“The method allows us to study the charge of individual particles and the forces acting between them. Other methods for studying these forces often require sophisticated instruments which cannot provide information down to the particle level,” says research leader Timur Shegai. 

Can provide new knowledge on everything from medicines to biosensors

Another way to use the platform, which is important for the development of many technologies, is to gain a better understanding of how individual particles interact in liquids and either remain stable or tend to stick to each other. It can provide new insights into the pathways of medicines through the body, or how to make effective biosensors, or water filters. But it is also important for everyday products that you do not want to clump together, such as cosmetics.

“The fact that the platform allows us to study fundamental forces and material properties shows its potential as a truly promising research platform,” says Timur Shegai.

In the lab, Michaela Hošková opens a box containing a finished sample of the platform. She lifts it with tweezers and shows how easily it can be placed in the microscope. Two thin glass plates hold everything needed to study nature’s invisible glue.

“What I find most exciting is that the measurement itself is so beautiful and easy. The method is simple and fast, based only on the movement of gold flakes and the interaction between light and matter,” says Michaela Hošková, zooming the microscope in on a gold flake, the colours of which immediately reveal the forces at play.

 

How the researchers study ‘nature’s invisible glue’

Gold flakes approximately 10 micrometres in size are placed in a container filled with a salt solution, i.e. water containing free ions. When a drop of the solution is placed on a glass substrate covered with gold, the flakes are naturally attracted to the substrate and nanometre-sized cavities (100-200 nanometres) appear. Self-assembly occurs as a result of a delicate balance between two forces: the Casimir force, a directly measurable quantum effect that causes objects to be attracted to each other, and the electrostatic force that arises between charged surfaces in a salt solution.

When a simple halogen lamp illuminates the tiny cavities, the light inside is captured as if in a trap. This allows the researchers to study the light more closely using an optical microscope connected to a spectrometer. The spectrometer separates the wavelengths of the light so that different colours can be identified. By varying the salinity of the solution and monitoring how the flakes change their distance to the substrate, it is possible to study and measure the fundamental forces at play. To prevent the saline solution with the gold flakes from evaporating, the drop of gold flakes and saline are sealed and then covered with another glass plate.

The platform was developed at Chalmers’ Nanofabrication Laboratory, Myfab Chalmers, and at the Chalmers Materials Analysis Laboratory (CMAL).

 

More about the research

The scientific article Casimir self-assembly: A platform for measuring nanoscale surface interactions in liquids has been published in PNAS (Proceedings of the National Academy of Sciences). It was written by Michaela Hošková, Oleg V. Kotov, Betül Küçüköz and Timur Shegai at the Department of Physics, Chalmers University of Technology, Sweden, and Catherine J. Murphy at the Department of Chemistry, University of Illinois, USA.

The research was funded by the Swedish Research Council, the Knut and Alice Wallenberg Foundation, the Vinnova Centre 2D-Tech and Chalmers University of Technology’s Nano Area of Advance.

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Journal

Proceedings of the National Academy of Sciences

DOI

10.1073/pnas.2505144122 

Method of Research

Experimental study

Subject of Research

Not applicable

Article Title

Casimir self-assembly: A platform for measuring nanoscale surface interactions in liquids

Video: The platform on which the forces can be seen through colours. [VIDEO] 

On the monitor, which is connected to the lab equipment, it is possible to see many gold flakes moving and changing to colours like red and green against the golden yellow background. The colours reveal the forces at play.

  

The Chalmers researchers’ new platform makes it possible to measure and study the forces that are usually referred to as nature’s invisible glue – what binds objects together at the smallest scales. When light is captured between two gold flakes, the researchers can study the delicate balance between two forces – one pulling the tiny objects towards each other and the other holding them apart. The joining force, the Casimir effect, makes the gold flakes connect to each other.  The second, electrostatic force, arise in the salt solution and prevents the flakes from sticking together completely. When those two forces balance each other, this is known as a self-assembly process, and the result is the cavity that opens up new research possibilities.

Credit

​​​​​​​Illustration: Chalmers University of Technoogy | Michaela Hošková

A platform of gold reveals the forces in nature’s invisible glue. Researchers at Chalmers University of Technology, Sweden, have discovered a quick and easy way to study the hidden forces that bind the smallest objects in the universe together. Using gold, salt water and light, they have created a platform on which the forces can be seen through colours.

When light is captured between micrometre-sized gold flakes in a salt solution, it is possible to study the delicate balance between two forces – one pulling the tiny objects towards each other and the other holding them apart. The joining force, the Casimir effect, makes the gold flakes connect to each other. The second, electrostatic force, arises the salt solution and prevents the flakes from sticking together completely. When those two forces balance each other, this is known as a self-assembly process and the result is the cavity that opens up new research possibilities.

In the lab at Chalmers, doctoral student Michaela Hošková shows a glass container filled with millions of micrometre-sized gold flakes in a salt solution. Using a pipette, she picks up a drop of the solution and places it on a gold-coated glass plate in an optical microscope. What happens is that the gold flakes in the salty solution are immediately attracted to the substrate but leave nanometre-sized optical spaces between them and the gold platform. The cavities created in the liquid act as resonators in which light bounces back and forth, displaying colours.  When the microscope’s halogen lamp illuminates the platform and a spectrometer separates the wavelengths, the different colours of light can be identified. On the monitor, which is connected to the lab equipment, it is now possible to see many flakes moving and changing to colours like red and green against the golden yellow background. The colours reveal the forces at play.

Credit

Chalmers University of Technology | Mia Halleröd Palmgren