Researchers watch a single catalytic grain do work in real time

A team of researchers from Washington State University and the U.S. Department of Energy's Pacific Northwest National Laboratory (PNNL) used a new probing technique to look at the surface of iron as it was exposed to oxygen to find out what makes one catalyst work better than another. The work is reported in the journal, Angewandte Chemie. It could eventually help engineers tune reactions better and develop new catalysts that don't rely on expensive precious and rare earth metals to make many everyday products.

"Essentially, this next-generation technique allows us to look at reactions in real-time while being chemically aware of what's going on," said Jean-Sabin McEwen, professor in the Gene and Linda Voiland School of Chemical Engineering and Bioengineering and a corresponding author on the work.

For many of the reactions used to create everyday food products, medicine, plastics, chemicals, and fuels, industry relies largely on past experience and accepted practices, said McEwen, who holds a joint appointment at PNNL. Catalytic processes, the reactions to make everyday products, are complex and poorly understood in many cases, and researchers often design catalysts with only limited understanding of their underlying mechanisms.

"We're trying to develop some basic and fundamental understanding that helps us narrow down how we approach the engineering of these kinds of materials or systems in a more efficient way," said Daniel Perea, co-author and a materials scientist with PNNL. "We want to make new types of chemicals more efficiently rather than just the 'cook and look' way."

Iron is a particularly important element which could eventually be used by industry to convert bio-oil, derived from plant materials, into usable bio-based fuels. It is abundant, inexpensive and can remove oxygen efficiently from bio-oil to produce biofuels. However, it also reacts easily with oxygen, leading to oxidation or rusting, which halts the reaction. The researchers have discovered that applying an electric field at the catalyst's surface can mitigate oxidation, creating an optimal environment for the reaction to continue without deactivation.

"You want it to be reactive, but not too reactive. It's like the Goldilocks rule -- you want something that's just right," said McEwen.

Using the new probing technique to look at the iron's surface, the researchers were able to see how much the iron oxidized, which crystal surfaces worked best, and how the electric fields influenced the reaction.

"We can look at all the different kinds of surfaces you can have on a single catalytic grain in real time, so this is much more realistic in modeling what we would see in real life in a real catalyst," said McEwen.

Because the atomic probing technique itself requires use of an electric field, the researchers realized they can exploit the electric field not just for the imaging, but also to control the amount of rust that is forming at its surface.

"We turned the tool into an instrument to allow us to look at reaction dynamics," said Perea. "We're laying down the foundation for being able to drive the science forward. But at the same time, we have our eye on the engineering applications."

PNNL scientist Sten Lambeets and WSU graduate students Naseeha Cardwell and Isaac Onyango led the research. The work was funded by the Catalysis Program within the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences, Biosciences and Geosciences and by the Laboratory Directed Research and Development program at PNNL.