Intermetallics with controlled microstructure and chemical composition afford unique catalytic properties, and thus are greatly desirable for heterogeneous catalysis. Identifying the key elementary steps of intermetallic process is a key step towards mechanistic clarification and mechanistic clarification.
Taking the advantages of real-world 1 bar pressure, gas and heating environment provided by the Climate in situ gas & heating solution, researchers from Shenyang National Laboratory for Materials Science (Chinese Academy of Sciences) and SynCat@Beijing realised atom-resolved imaging and electron energy-loss spectrum acquiring from a single PdZn intermetallic nanoparticle under H2 atmosphere and at elevated temperature, by employing a mid-range TEM operated at 200 keV. The results were also compared with in-situ X-ray diffraction and X-ray photoelectron spectroscopy analysis. The quasi-correlation investigations sketch a full picture of the phase transitions from Pd to PdZn via the intermediate PdHx under hydrogen atmosphere.
The ability of capturing the intermediate state during the reaction condition, not only discloses the microstructural information in reference to the catalyst activation in detail but also sheds light on rational design and the optimum synthesis of intermetallic compound catalysts.
Related results have been accepted for publication in Angewandte Chemie International Edition.
Substrate-supported noble metal single-atom catalysts (SACs) are widely used in many important chemical reactions for their high activity and selectivity. However, the fabrication of high concentration of single-atom catalysts (SACs) with long-term stability remains a challenge. For example, at the working conditions, usually calcination at a high temperature, the supported SACs migrate and coarsen (a process named Ostwald ripening), resulting in a decreased catalytic performance. Writing in Nature Communications, researchers from Dalian Institute of Chemical Physics (Chinese Academy of Sciences) and Tianjin University of Technology, found that the high- temperature calcination of Pt nanoparticles on reductive Fe 2 O 3 substrate in air is favorable for the formation of high concentrations of thermally stable Pt SACs, which is different from the traditional Ostwald ripening. By employing the Climate in situ gas & heating solution and HAADF-STEM imaging, they directly observed the disintegration of Pt nanoparticles at 800 °C under a flow of 1 bar O 2 . During the in- situ reaction process, they found particle disappearance occurs in the absence coalescence, implying the genesis of atomically-dispersed Pt entities. The in-situ results are in good agreement with the ex-situ characterizations and theoretical calculations. The new findings provide a new route to fabricate high-metal-loading and thermal stable SACs for a wide range of industrially important catalytic reactions.
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The efficiency of a catalyst relies on the capability of promoting reactions directly on its surface. Thus, there have been many attempts to accurately determine the atomic structure at the surface when gasses are flown on the catalytic sample.
Obviously, in situ electron microscopy is the best candidate to provide that answer, due to the possibility of recording ultra high resolution information while flowing gasses on the sample at high temperature. However, due to the nature of the imaging process, only 2D projections can be captured, severely limiting our understanding of the catalytic process.
Researchers at EMAT, Antwerp, have combined the high stability of the Climate in situ gas&heating solution with their multi-year experience on developing algorithms to accurately retrieve 3D structures down to atomic resolution. Platinum nanoparticles were cyclically exposed to reducing and oxidizing gas mixtures to promote and study surface re-faceting; after each step, high resolution STEM images were acquired and they were analyzed by means of a novel methodology based on deep convolutional neural networks (CNN) and molecular dynamics simulations.
The results show that it is now possible to obtain very accurate 3D atomic models that enable researchers to “see and count” atoms which are sitting on the surface. These new findings will allow a much deeper characterization and understanding of the processes behind catalytic reactions.
In situ liquid experiment featuring Copper deposition. It can be seen that high flow rates (1200 nl/min) promote plating of the electrode. However, when switching to lower flow rate values (50 nl/min) the growth mechanism changes and dendrites appear. The pressure-based liquid pump, the absence of dead volumes and the defined liquid channel all contribute to a very responsive system that allows to accurately vary experimental conditions within seconds.
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The image was acquired just before the launch of the improved heating chip. The sample is a gold-palladium nanoparticle imaged at 1000 °C on a Thermo Scientific Titan equipped with an image corrector and our Wildfire in situ heating system. We selected this image because it shows that the native resolution and drift rate of your microscope are not affected at all by the extreme temperatures that are possible with the DENSsolutions Wildfire system.
Courtesy of EMAT, Antwerp (BE)
Flexoelectrics: the sample imaged is Bi1/2Na1/2TiO3 – SrTiO3 (aka BNT-ST). It went through a thermal treatment directly on the chip in order to obtain the desired properties, then it was imaged at 800 °C with electric fields ranging from -220 kV/cm to +220 kV/cm. Images were acquired using the Lightning HB+ on a JEOL ARM. The image was chosen because it explains why we need to have the flexibility to reach extreme conditions, both in terms of temperature and electric fields. The sample showed, unexpectedly, nano-domains at temperatures much higher than previously reportedl.
Courtesy of Leopoldo Molina-Luna, TU Darmstadt (DE)
The image shows a Pd particle imaged system at 500 C in 1 bar of He/CO. The image was recorded with our Climate G+ on a Thermo Scientific Titan. Although having 1 bar inside the Nano-Reactor may lead to think that the native resolution of your microscope will be affected, the image demonstrates an information transfer of 55 pm. Thus, the Climate enables users to observe the finest dynamical structural changes in catalytic processes..
Courtesy of Prof. Wang, Zheijang University (CN)
The image captured from a video shows a protein, ferritin, imaged with our in situ liquid solution on a JEOL 2110F equipped with a direct electron detector camera. The protein has an outer diameter of 12 nm and we can image it with a resolution not too far from 1 nm. We can observe brownian motion, rotation, agglomeration and fusion, thanks to the stability and reliability of our in situ liquid solution.
Courtesy of Prof. Battaglia, UCL (UK)