Real-time observation of hydrocarbon polymerization

The polymerization of hydrocarbons into linear chains lies at the heart of many industrially relevant chemical reactions. One prominent example is the alkene polymerization with the Ziegler Natta catalysts, which is responsible for 2/3 of the global production of polyolefins. Long-chain hydrocarbons can also be produced from syngas (a mixture of carbon monoxide and hydrogen) through the so-called Fischer-Tropsch synthesis (FTS), occurring typically on cobalt-based catalysts. This process is experiencing a renewed interest, especially in the context of modern power-to-gas and power-to-liquid plants.

From a microscopic point of view, the identification of the complex series of reaction steps involved in the polymerization of small molecules into long hydrocarbon chains is still under debate. Surface-science techniques have proved to be extremely powerful to explore the mechanisms of heterogeneous catalysis. However, due to the harsh reaction conditions of FTS, analysis using such techniques poses a real experimental challenge.

Though the step sites of the catalytic surface are also commonly assumed to promote the C-C coupling of CHx monomers, the typical strong adsorption of small molecules at the step edges could trap the CHx species, hindering the polymerization. This behavior can be understood in the framework of the Sabatier’s principle, stating that if the adsorption energy of the substrate is too low, then the catalytic activity is suppressed; if it is too large, then the product will not desorb and blocks the surface, leading to catalyst poisoning. Therefore, elucidating the actual role of the step sites is crucial for an in-depth atomistic understanding of the hydrocarbon chain growth process.

Here we investigated the formation of hydrocarbon chains resulting from acetylene polymerization on a Ni(111) model catalyst surface. Exploiting X-ray photoelectron spectroscopy (XPS) performed at the SuperESCA beamline of Elettra, the intermediate species and reaction products have been directly identified. This has been enabled by the high energy resolution (about 100 meV) of the instrument, allowing resolving vibrational fine structures.

Read more on the Elettra website

Advanced Light Source upgrade approved to start construction

Berkeley Lab’s biggest project in three decades now moves from planning to execution. The ALS upgrade will make brighter beams for research into new materials, chemical reactions, and biological processes.

The Advanced Light Source (ALS), a scientific user facility at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), has received federal approval to start construction on an upgrade that will boost the brightness of its X-ray beams at least a hundredfold.

“The ALS upgrade is an amazing engineering undertaking that is going to give us an even more powerful scientific tool,” said Berkeley Lab Director Michael Witherell. “I can’t wait to see the many ways researchers use it to improve the world and tackle some of the biggest challenges facing society today.”

Scientists will use the upgraded ALS for research spanning biology; chemistry; physics; and materials, energy, and environmental sciences. The brighter, more laser-like light will help experts better understand what’s happening at extremely small scales as reactions and processes take place. These insights can have a huge array of applications, such as improving batteries and clean energy technologies, creating new materials for sensors and computing, and investigating biological matter to develop better medicines.

“That’s the wonderful thing about the ALS: The applications are so broad and the impact is so profound,” said Dave Robin, the project director for the ALS upgrade. “What really excites me every day is knowing that, when it’s complete, the ALS upgrade will enable researchers to make scientific advances in many different areas for the next 30 to 40 years.”

The DOE approval, known as Critical Decision 3 (CD-3), formally releases funds for purchasing, building, and installing upgrades to the ALS. This includes constructing an entirely new storage ring and accumulator ring, building four feature (two new and two upgraded) beamlines, and installing seismic and shielding upgrades for the concrete structure housing the equipment. The $590 million project is the biggest investment at Berkeley Lab since the ALS was built in 1993.

Read more on the Berkeley Laboratory website

Image: The upgrade to the Advanced Light Source at Berkeley Lab will add two new particle accelerator rings within the iconic building’s footprint. 

Credit: Thor Swift/Berkeley Lab

Watching nanoparticle chemistry and structure evolve

Using a multimodal approach developed at the Advanced Light Source (ALS), researchers learned how chemical properties correlate with structural changes during nanoparticle growth.

The work will enable a greater understanding of the mechanisms affecting the durability of nanoparticles used to catalyze a broad range of chemical reactions, including clean-energy reactions.

Catalyzing technological progress

In applications ranging from chemical synthesis to energy storage, catalysts enable chemical reactions to run at more favorable temperatures, pressures, or in general, with lower energy requirements. For example, catalysts enable the efficient splitting of water to generate hydrogen, which can then be used as a clean, decarbonized fuel.

For such applications, nanoparticles on the surface of a transition-metal oxide work well as catalysts, but they are susceptible to coarsening, agglomeration, and other forms of degradation, shortening their usable lifetime. In this work, researchers applied a technique they developed at the ALS to simultaneously study the chemistry and structure of catalyst materials as they form, a capability that will help scientists identify strategies for improving nanoparticle durability.

Understanding nanoparticle exsolution

A process called “exsolution” has shown significant promise for controlling nanoparticle size, shape, distribution, and stability. Briefly, the process involves causing dopant atoms in a host matrix to migrate to the surface and gather to form nanoparticles. This is done by heating the host material under reducing conditions (i.e., in a reducing gas such as hydrogen). Exsolution from metal oxide hosts produces highly stable metal nanoparticles that are often partially embedded in the oxide surface and show high activity for the oxygen evolution reaction (OER), a key step in many electrochemical reactions, including water splitting.

Here, the samples studied were thin films of SrTi0.9Nb0.05Ni0.05O3-δ (STNNi). When STNNi is heated in H2 gas, the Ni atoms migrate to the surface and form nanoparticles. Before the reducing treatment, such samples are inactive with respect to the OER. After treatment, the system becomes active, despite a relatively small amount of Ni doping.

Read more on the ALS website

Image: Atomic force microscope images of nickel- and niobium-co-doped strontium titanate, before (left) and after (right) thermal treatment in a reducing (H2) atmosphere. After treatment, bright features consistent with the formation of nickel nanoparticles are observed.

A piece of PSI history sets off on a long journey

Safely packed in a sturdy wooden crate, a high-tech component from PSI has begun its journey to Australia. The device was in use at PSI for more than ten years – now, with the commissioning of the Swiss X-ray free-electron laser SwissFEL, it has reached the end of its service life and will be given a new task at the Australian Synchrotron in Melbourne.

The device is carefully lifted by the indoor crane. The weight displayed on the crane’s external screen shoots up and down, eventually settling down at about 11.5 tonnes. The weight of this so-called insertion device is mainly due to its heavy steel frame. The magnets installed inside this generate attractive forces of several tonnes. The device must be able to withstand this enormous field strength. In particle accelerators, the periodic arrangement of the magnets is used to deflect electrons, thereby generating synchrotron radiation – a special type of X-rays.

Pioneering work at PSI

At PSI, the insertion device was used for a very special purpose, however. Following a lecture by an American colleague on the generation of ultra-short X-ray pulses, the two PSI physicists Gerhard Ingold and Thomas Schmidt realised that the conditions at the Swiss Light Source SLS were ideal for such a technique. The technology is called femtoslicing, and it can be used to observe extremely fast processes, such as chemical reactions.

“Immediately after the lecture was over, we did our first calculations. A few days later, the calculations turned into a project and three years later, under the leadership of Gerhard Ingold, we were finally able to produce hard X-rays in the femtosecond range for the first time in the world – a pulse of high-energy X-rays lasting 0.000 000 000 000 1 second,” as the head of the Insertion Device Group at PSI, Thomas Schmidt, recalls. Their approach was based on using the powerful magnetic field produced by this device as a modulator, so as to achieve resonance between the electrons and an external infrared laser, thereby transferring the pulse length of the latter to the X-rays. Since only a small fraction of the electrons are used in this process, namely those that overlap with the laser pulse, the technique is referred to as “slicing”.

The project resulted in numerous publications. Experiments were carried out on a range of different samples and new types of detectors were developed in order to process the extremely fast units of information. These findings were ultimately crucial to the development of free electron lasers, which are driven by linear accelerators and thus indirectly also the Swiss X-ray free-electron laser SwissFEL, where the first pilot experiments were carried out in 2017. However, this also heralded the end of the Femtoslicing Facility and thus of the insertion device in question. “SwissFEL allows us to generate much brighter and even shorter pulses of this kind of radiation than with the original facility. With this, extremely fast processes can be imaged at even higher resolutions,” says Thomas Schmidt.

Since then, the insertion device has been sitting in the hall of the SLS, unused.

Important manufacturer based in Siberia

Insertion devices are high-precision instruments, and demand for them is limited. Because of this, only a few manufacturers in the world are prepared to take on the complex task of building these devices in the first place. The world’s most important supplier of superconducting wigglers (a special type of insertion device) is based in Russia. However, due to the war and the global sanctions against Russia, many countries have also stopped importing these rare devices.

“Suddenly, there was a demand for retired wigglers in our European network for synchrotron radiation sources (LEAPS – League of European Accelerator-based Photon Sources),” explains Thomas Schmidt. “First, SOLARIS, the National Synchrotron Radiation Centre in Poland, inquired about a device that was no longer needed – we immediately agreed and sent them the plans. Unfortunately, our device was not compatible with their facility.” But just a short while later, the Australian Nuclear Science and Technology Organisation got in touch, also asking for a wiggler for their synchrotron in Melbourne. Again plans were sent – and this time everything fitted.

Read more on the PSI website

Image: Thomas Schmidt in the hall of the Swiss Light Source SLS. The insertion device weighing several tonnes can be seen suspended in the background, ready for transport. After being used for research at PSI more than ten years, this high-tech device will be given a new home at the Australian Synchrotron in Melbourne.

Credit: Paul Scherrer Institute/Mahir Dzambegovic

Athos just got even better

An upgrade at the soft X-ray beamline of the free electron laser SwissFEL will open up new experimental capabilities. Using an external laser system to ‘seed’ the emission of X-ray photons, and thus imprint well-defined optical properties on the beam, the upgrade gives the Athos beamline unprecedented stability. With this, ultra-fast ‘attosecond’ timescales that probe the movements of electrons in chemical reactions become possible.

Free electron lasers (FELs) in the X-ray regime, such as the X-ray free electron laser SwissFEL, produce short pulses of brilliant light that give unique insights into the structure and dynamics of materials through so-called ‘molecular movies’. The Athos beamline of SwissFEL produces so-called ‘soft’ X-rays whose comparatively low photon energies are useful for studying the interactions between molecules.

A limitation for the Athos beamline, as for almost all FELs, is stability. The reason for this comes down to the process by which light is made: a process called self-amplified spontaneous emission (SASE). In a FEL, electrons, accelerated to close to the speed of the light, are wiggled by a series of magnets, called undulators. Once wiggling, they produce photons: at SwissFEL, in the form of X-rays. SASE describes the process by which these photons repeatedly interact with the electron beam and stimulate – or ‘seed’ – the emission of more photons in subsequent parts of the electron beam. The spontaneous emission of radiation in this way is a stochastic process. This means that the X-ray beam created is inherently unstable, characterised by variations in wavelength and pulse energy.

Thanks to funding from the European Research Council (ERC), a new upgrade of Athos tackles this fundamental challenge of X-ray FELs. The upgrade forms part of the HERO project, which in 2018 was awarded a prestigious Synergy grant of 14 million Euros and incorporates principal investigators from PSI, EPFL, ETHZ and Stockholm. Standing for ‘Hidden, Entangled and Resonating Orders’, the HERO project, which is coordinated by PSI, aims to uncover hidden quantum properties in materials that cannot be studied with existing methods. The HERO upgrade of the Athos beamline will enable such new insights.

“What is demonstrated here is the power of funding for blue-skies research that the ERC uniquely provides to associated countries,” states Gabriel Aeppli, head of the Photon Science Division at PSI, who is the coordinating principal investigator for the HERO project.

Bringing Athos in line

In a classroom, one particularly well-behaved child can serve as a role model for all the children. In a similar vein, at the Athos beamline, the upgrade uses an external laser to imprint its well-behaved properties on the FEL beam. Instead of relying on the stochastic, spontaneous emission of radiation, a ‘seed-laser’ interacts with the wiggling electron beam to amplify the emission of radiation. As this external, optical laser has a well-defined pulse and coherence properties, it can transfer these to the emitted X-rays.

There is a reason that an X-ray FEL has never before been externally seeded. “Although the principle of ‘seeding’ a FEL is not entirely new, seeding a FEL at an energy range as high as this is,” explains Alexandre Trisorio, head of the gun laser group, who developed the seed-laser system. “The trouble is that there are no external laser sources that operate in the right wavelength range”.

To get around this, the scientists – through some serious feats of electron bunch gymnastics and tricks of the light – are employing a technique known as echo-enabled high-harmonic generation (EEHG), whereby higher frequency resonances are created that seed the FEL. The full upgrade is a two phase project, the first of which has now been successfully completed.

Read more on the PSI website

Image: An X-ray FEL cannot be seeded with a simple optical laser: there is none that can deliver a short enough wavelength. So, more complicated techniques are required. In a dedicated room alongside the Athos beamline, an 11m optical bench will host two titanium sapphire seed laser systems. Martin Huppert fine tunes the first of these, installed in the first phase of the HERO upgrade.

Credit: Paul Scherrer Institute / Markus Fischer