New Micro-Reactor Will Help Study Catalytic Nanoparticles

This high-resolution transmission electron micrograph reveals the arrangement of cerium oxide nanoparticles (bright angular
This high-resolution transmission electron micrograph reveals the arrangement of cerium oxide nanoparticles (bright angular "slashes" at the bottom of the image) supported on a titania substrate (background)‹a combination being explored as a catalyst for splitting water molecules to release hydrogen as fuel and for other energy-transformation reactions. (Credit: Brookhaven National Laboratory)

Anatoly Frenkel, a professor of physics at Yeshiva University, is collaborating with materials scientist Eric Stach and others at the U.S. Department of Energy’s Brookhaven National Laboratory to develop new ways to study the behavior of catalytic nanoparticles.

“We are developing a new ‘micro-reactor’ that enables us to explore many aspects of catalytic function using multiple approaches at Brookhaven’s National Synchrotron Light Source (NSLS), the soon-to-be-completed NSLS-II, and the Center for Functional Nanomaterials (CFN),” said Stach, who works at the CFN. “This approach lets us understand multiple aspects of how catalysts work so that we can tweak their design to improve their function. This work could lead to big gains in energy efficiency and cost savings for industrial processes.”

Until now, the methods for understanding the properties of catalytic nanoparticles could only be used one at a time, with the catalyst ending up in a different state for each of the experiments. This made it difficult to compare information obtained using the different instruments. The new micro-reactor will employ multiple techniques—microscopy, spectroscopy, and diffraction—to examine different properties of catalysts simultaneously under operating conditions. By keeping catalytic nanoparticles in the same structural and dynamic state under the same reaction conditions, the micro-reactor will give scientists a much better sense of how they function.

“These developments have resulted from the combination of unique facilities available at Brookhaven,” said Frenkel. “By working closely with Eric, we realized that there was a way to make both x-ray and electron-based methods work in a truly complementary fashion.

Eric Stach and Dmitri Zakharov of the CFN with Anatoly Frenkel of Yeshiva University and his postdoc, Yuanyuan Li, sitting at the Titan 80/300 Environmental Transmission Electron Microscope at the Center for Functional Nanomaterials.

Eric Stach and Dmitri Zakharov of the CFN with Anatoly Frenkel of Yeshiva University and his postdoc, Yuanyuan Li, sitting at the Titan 80/300 Environmental Transmission Electron Microscope at the Center for Functional Nanomaterials. (Credit: Brookhaven National Laboratory)

Each technique has strengths, Stach explained. “At the NSLS, using powerful beams of x-rays, we can tell how the entire group of nanoparticles behaves, while electron microscopy at the CFN lets us see the atomic structure of each nanoparticle. By having both of these views of the catalysts we can more clearly understand the relationship between catalyst structure and function.”

Said Frenkel, “It was very satisfying for us to conduct the first tests with the reactor at each facility and receive positive results. I am particularly grateful to Ryan Tappero, the scientist who runs NSLS beamline X27A, for his expert help with x-ray data acquisition.”

Frenkel has had an ongoing collaboration with scientists at Brookhaven. Last year, with post-doctoral research associate Qi Wang, Frenkel and Stach measured properties of catalytic nanoparticles using the x-rays produced by the NSLS as well as atomic-scale imaging with electrons at the CFN. As reported in a paper published in the Journal of the American Chemical Society earlier this year, they discovered that rather than changing completely from one state to another at a certain temperature and size, as had been previously believed, there is a transition zone between states when particles are changing forms.

“This is of significance fundamentally because until now, the structures were known to merely change from one form to another—they were never envisioned to coexist in different forms,” Frenkel said. “With our information we can explain why catalysts often don’t work as expected and how to improve them.”

Li L., Wang L.L., Johnson D.D., Zhang Z., Sanchez S.I., Kang J.H., Nuzzo R.G., Wang Q., Frenkel A.I., Li J., Ciston J., Stach E.A., & Yang J.C. (2013). Noncrystalline-to-crystalline transformations in Pt nanoparticles. Journal of the American Chemical Society, 135 (35), 13062-72 PMID: 23869582

The above story is based on or reprinted from materials provided by Brookhaven National Laboratory. Original article by Karen McNulty Walsh.

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