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Taking the High Road by Finding the Middle Ground

Yi Lu drives to answer tough questions about the roles of mesoscale interactions in natural catalysts
By Kristin Manke

cobalt based catalyst
With his colleagues, Lu is designing artificial catalysts that perform as well as their natural counterparts in driving reactions that store and release energy in chemical bonds. In some cases, Lu's catalysts actually outperform their natural counterparts.

Even on the coldest, snowiest of days, plants and microbes host reactions that generate chemicals while producing little waste. Yet in manufacturing complexes, the same reactions require much higher temperatures and pressures, and generate much more waste. The difference is the catalysts. Dr. Yi Lu has been interested in how such catalysts work, both in natural and industrial plants, since he was a teen in China and through his graduate work at the University of California at Los Angeles.

Lu now holds a joint appointment with Pacific Northwest National Laboratory (PNNL) and the University of Illinois at Urbana-Champaign. The appointment offers the university professor and Royal Society of Chemistry Fellow opportunities to work across an array of disciplines at PNNL. It also gives him access to specialized research facilities available at PNNL. Further, joint appointments offer the chance for close collaboration with PNNL experts and rising stars in different areas of catalysis as well as physics, chemical theory, and computational science (see article on joint appointments).

Throughout his career, Lu has worked with students and senior scientists to learn the secrets of natural catalysts. He wants to know how nature drives reactions and how an understanding of natural catalysts could be applied to design what's needed to produce fuels and alternative energies.

"Without catalysts, we can't even talk about alternative energy," said Lu.

The structure of a natural catalyst is complex. Looking at the larger structure, a protein, the starting substrates travel through different environments to get to the active site. This is a relatively small area, most likely containing metal ions. The resulting products weave back out through the protein. Scientists call the environment surrounding the active metal-binding site the outer coordination spheres.

"A lot of progress has been made in making small molecular catalysts and in understanding large protein enzymes, each has its own advantages and disadvantages," Lu said. "I wanted to combine the benefits of what has been learned about the small molecular catalysts with the large proteins and find the middle ground."

Lu and his colleagues demonstrated that an understanding of the outer coordination spheres—a mesoscale view of the catalyst—can't be ignored if the goal is to create working catalysts. "We are not here to just make a catalyst that looks like a native enzyme," said Lu. "We are here to create something that does what nature does and then go beyond."

The challenge, in part, is the entangled nature of the interactions in the outer coordination sphere. Some of the interactions are vital. Some aren't. Some interactions boost the performance of nearby reactivity. Others stop or slow the reaction. And it can all change based on different conditions. In addition, the forces involved are weak, making them difficult to find or measure. "They are hidden and difficult to understand experimentally. In addition to that already difficult problem, the theory and principles that explain the behavior are not well developed," Lu said.

While the challenge is the jumbled nature of the interactions, the solution revolves around using powerful instruments. For Lu, many of these resources were available at PNNL located in Washington State, including DOE's Environmental Molecular Sciences Laboratory (EMSL), a scientific user facility.

"EMSL led me to PNNL," said Lu. "I first learned about the lab through my user proposals at EMSL, which is really the best facility in the world for solving some of the tough problems that interest me." As he worked with the resources at EMSL, Lu began to meet more and more catalysis experts at PNNL, including Wendy Shaw, Simone Raugei, Bojana Ginovska, Aaron Appel, and Molly O'Hagan.

The chance to have spirited discussions about both current strategies and future directions of catalysis research continues to energize Lu. He's chaired a recent Gordon Research Conference on Metals in Biology. He discusses research as a member of eight editorial boards of journals with diverse subjects from computational design to synthesis and then characterizations of catalysts. At PNNL, these discussions are leading to exciting options to revise the outer layers of catalysts to add new chemical functionality.

Further, the collaborations and resources to map out the details of the mesoscale interactions led Lu and his colleagues to discover forces that influence the reactivity and selectivity of catalysts. Forces surrounding the active site offer up a way to control catalytic reactivity at the active site. In particular, his work focuses on tuning these weak forces in the mesoscale to control the withdrawal or donation of electrons to the metal and thus its redox potentials, which is a key to successful catalysis.

For example, Lu and others designed a catalyst with a copper and iron active site. They placed the catalyst in a fuel cell, which uses oxygen and hydrogen to create electricity. They tuned the weaker forces, resulting in artificial proteins that can match or even exceed functional properties of native ones.

Further, Lu is leading work that sheds new light on the nuances of the active site itself. For example, he is designing a colorful protein. It can display all the colors of the spectrum. In addition to being beautiful, subtle changes in intensity and color tell Lu and his team a lot about the active site. "The more we know, the better we are able to understand and the better we are able to design more effective catalysts," said Lu.

Where is this all leading? "Nature doesn't have an alternative energy problem, we do," said Lu. If we can learn the secrets of natural catalysts—such as which interactions must be controlled, which can be ignored—we can design catalysts and materials needed to harness sunlight, oxygen, water and other natural sources of energy to create the electricity, fuels, and chemicals we need.

About the author: Kristin Manke is a science writer and technical communicator at Pacific Northwest National Laboratory with more than 20 years of experience in writing about chemistry, whether it is fundamental research or applied work that's part of nuclear cleanup.

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