The experiment has revealed for the very first time how the chemical structure of the surface of a specific nanoparticle modifications under reaction conditions, making it more active. Using X-rays from the European Synchrotron Radiation Facility ESRF in Grenoble, France, the team was not only able to produce a detailed image of the nanoparticle; it also determined the mechanical strain within its surface. “The surface strain is related to the surface area composition, in particular the ratio of platinum to rhodium atoms,” describes co-author Philipp Pleßow from the Karlsruhe Institute of Technology (KIT), whose group computed stress as a function of surface area composition. The different surface areas of a nanoparticle are called aspects, just like the elements of a cut gemstone.
The X-ray light produces a characteristic diffraction pattern from which changes in the surface tension and thus in the chemical structure of the surface area throughout operation can be read.
” In spite of their extensive usage and great value, we are still ignorant of numerous crucial information of just how the numerous catalysts work,” describes Stierle, head of the DESY NanoLab. “Thats why we have actually long wished to study genuine drivers while in operation.” This is challenging, because in order to make the active surface area as large as possible, drivers are typically utilized in the type of small nanoparticles, and the changes that impact their activity occur on their surface area.
Surface area stress associates with chemical composition
In the framework of the EU project Nanoscience Foundries and Fine Analysis (NFFA), the team from DESY NanoLab has established a strategy for labeling private nanoparticles and thus determining them in a sample. “For the research study, we grew nanoparticles of a platinum-rhodium alloy on a substrate in the lab and labeled one specific particle,” states co-author Thomas Keller from DESY NanoLab and in charge of the project at DESY “The diameter of the labeled particle is around 100 nanometres, and it resembles the particles utilized in a cars catalytic converter.” A nanometre is a millionth of a millimeter.
Close-up view (artists impression) of the nanoparticle under investigation: Carbon monoxide oxidizes to co2 on the surface area of the nanoparticle. Credit: Science Communication Lab for DESY
Utilizing X-rays from the European Synchrotron Radiation Facility ESRF in Grenoble, France, the team was not just able to create a comprehensive picture of the nanoparticle; it also determined the mechanical stress within its surface. “The surface strain is connected to the surface structure, in particular the ratio of platinum to rhodium atoms,” explains co-author Philipp Pleßow from the Karlsruhe Institute of Technology (KIT), whose group calculated pressure as a function of surface area composition. By comparing the observed and calculated facet-dependent pressure, conclusions can be drawn concerning the chemical structure at the particle surface. The various surfaces of a nanoparticle are called elements, similar to the aspects of a cut gemstone.
When the nanoparticle is grown, its surface area consists mainly of platinum atoms, as this configuration is energetically preferred. The scientists studied the shape of the particle and its surface area pressure under different conditions, including the operating conditions of a vehicle catalytic converter. To do this, they heated the particle to around 430 degrees Celsius and allowed carbon monoxide and oxygen molecules to pass over it. “Under these reaction conditions, the rhodium inside the particle ends up being mobile and migrates to the surface area because it connects more strongly with oxygen than the platinum,” discusses Pleßow. This is also predicted by theory.
Animation: In operation, (diatomic) carbon monoxide particles oxidize to (triatomic) carbon dioxide molecules on the taken a look at particle. The X-ray light produces a particular diffraction pattern from which changes in the surface area stress and therefore in the chemical structure of the surface during operation can be read. Credit: Science Communication Lab for DESY.
” As a result, the surface pressure and the shape of the particle change,” reports co-author Ivan Vartaniants, from DESY, whose team transformed the X-ray diffraction data into three-dimensional spatial images. “A facet-dependent rhodium enrichment takes location, where extra corners and edges are formed.” The chemical structure of the surface area, and the shape and size of the particles have a significant impact on their function and efficiency. Nevertheless, scientists are only simply beginning to comprehend precisely how these are linked and how to control the structure and composition of the nanoparticles. The X-rays permit scientists to find modifications of just 0.1 in a thousand in the stress, which in this experiment corresponds to an accuracy of about 0.0003 nanometres (0.3 picometres).
Vital step towards examining commercial catalyst products
” We can now, for the very first time, observe the information of the structural changes in such driver nanoparticles while in operation,” states Stierle, Lead Scientist at DESY and professor for nanoscience at the University of Hamburg. “This is a significant action forward and is helping us to understand an entire class of reactions that use alloy nanoparticles.” Scientists at KIT and DESY now want to explore this methodically at the new Collaborative Research Centre 1441, funded by the German Research Foundation (DFG) and entitled “Tracking the Active Sites in Heterogeneous Catalysis for Emission Control (TrackAct).”.
” Our investigation is an important action towards examining commercial catalytic products,” Stierle points out. With DESYs prepared X-ray microscopic lense PETRA IV, we will be able to look at ten times smaller sized specific particles in real drivers, and under response conditions.”.
Reference: “Single alloy nanoparticle x-ray imaging during a catalytic reaction” by Young Yong Kim, Thomas F. Keller, Tiago J. Goncalves, Manuel Abuin, Henning Runge, Luca Gelisio, Jerome Carnis, Vedran Vonk, Philipp N. Plessow, Ivan A. Vartaniants and Andreas Stierle, 1 October 2021, Science Advances.DOI: 10.1126/ sciadv.abh0757.
X-ray analysis provided a total 3D picture of a specific driver nanoparticle and exposed changes in its surface tension and surface area chemical structure during different moduses operandi. Credit: Science Communication Lab for DESY
X-rays reveal compositional changes on active surface under reaction conditions.
A DESY-led research study group has actually been using high-intensity X-rays to observe a single catalyst nanoparticle at work. The experiment has actually revealed for the first time how the chemical composition of the surface area of a private nanoparticle changes under response conditions, making it more active. The group led by DESYs Andreas Stierle exists its findings in the journal Science Advances. This research study marks an important step towards a much better understanding of real, industrial catalytic products.
Rebuilt 3D image of the examined nanoparticle from the X-ray analysis (click to begin animation). Credit: DESY, Ivan Vartaniants
Drivers are materials that promote chemical reactions without being consumed themselves. Today, catalysts are used in many commercial processes, from fertilizer production to producing plastics.
