Anatoly Frenkel Pioneers New Technique to Track Chemical Reactions Under Real Operating Conditions Dr. Anatoly Frenkel, professor of physics at Yeshiva University, is a member of a scientific team that has pioneered a new technique revealing atomic-scale changes during catalytic reactions in real time and under real operating conditions.

Dr. Anatoly Frenkel, second from right, and Dr. Yuanyuan Li, right, are part of a team of scientists conducting cutting-edge research on catalytic reactions (photo: Brookhaven National Laboratory.)

Frenkel, along with collaborators Dr. Eric Stach, a scientist at Brookhaven National Laboratory, and Professor Ralph Nuzzo of the University of Illinois at Urbana-Champaign, combined two seemingly incompatible techniques, x-ray absorption spectroscopy and electron microscopy, to create an unprecedented, real-time “movie” of a common chemical reaction. The results demonstrate a powerful operando technique—from the Latin for “in working condition”—that may revolutionize research on catalysts, batteries, fuel cells and other major energy technologies. “Understanding why some catalysts are efficient and some are not is the grand challenge in energy science because solving it would offer opportunities for the rational design of low-cost, efficient catalysts that will decrease our national economy’s reliance on fossil fuels,” said Frenkel, a lead author in this study, who directed the x-ray spectroscopy investigations. “Solving it is, however, very difficult, because of the very small size of catalytic particles and inability of each individual technique to provide a complete picture. Imagine that you are trying to describe the three-dimensional shape of a cylinder by shining light at it and seeing only its shadow on the wall--depending on where the light source is located, the shape might be a circle or even a rectangle. Only by combining several projections can you 'recover' the true shape. In this work, we adopted essentially the same approach: we used a special reactor that allowed multiple techniques to 'shine light' at the catalyst so we could study its composition and fate during the course of the reaction.” The results of the study were published online in the journal Nature Communications. Dr. Yuanyuan Li, a postdoctoral research associate studying with Frenkel, was first author on the paper. “I feel honored to have been taken part in this high level research, which was a challenge but also absolutely intriguing to me,” she said. “In this work, Anatoly led us in solving problems with determination. I learned a lot from him: analytical methods, divergent thinking, and how to be a group leader. The most exciting part of this work is showing the importance of combining multiple operando probes, even with a well-examined catalytic system. Various reactions, interactions and changes are going on in a catalytic reaction and can only be caught when technologies are combined.” To prove the efficacy of this new mosquito-sized reaction chamber—called a micro-reactor—the scientists tracked the performance of a platinum catalyst during the conversion of ethylene to ethane, a model reaction relevant to many industrial processes. They conducted x-ray studies at the National Synchrotron Light Source (NSLS) and electron microscopy at the Center for Functional Nanomaterials (CFN), both Department of Energy Office of Science User Facilities. Frenkel led the x-ray experiments, in which a beam of x-rays bombards the catalyst sample and deposits energy as it passes through the micro-reactor. The sample then emits secondary x-rays, which are measured to identify its chemical composition—in this instance, the distribution of platinum particles. “The transmission electron microscopy (TEM) and x-ray absorption spectroscopy (XAS), analyzed together, let us calculate the numbers and average sizes of not one, but several different types of catalysts,” said Frenkel. “Running the tests in an operando condition lets us track broad changes over time, and only the combination of techniques could reveal all catalytic particles.” The new micro-reactor was specifically designed and built to work seamlessly with both synchrotron x-rays and electron microscopes. “Everything was exquisitely controlled at both NSLS and CFN, including precise measurements of the progress of the catalytic reaction,” Frenkel said. “For the first time, the operando approach was used to correlate data obtained by different techniques at the same stages of the reaction.” Added Stach, another lead author of this study, “In the past, scientists would look at data before and after the reaction under model conditions, especially with TEM and make educated guesses. Now we can make definitive statements.” The collaboration has already extended this operando micro-reactor approach to incorporate two additional techniques—infrared and Raman spectroscopy—and plans to introduce other complex and complementary x-ray and electron probe techniques over time. In the near future, this same micro-reactor approach will be used to explore other crucial energy frontiers, including batteries and fuel cells.