A catalyst for high-impact science

Early 2011 marked the launch of two new EMSL Research Campaigns, one of which is wholly dedicated to catalysis science. The campaign team recently achieved promising first results in their effort to gain direct insights into catalytic reactions on the surfaces of advanced metal oxide-based materials. This target was chosen for its relevance to the advancement of more efficient, less costly catalysts—a need with cross-cutting industrial applications.

The importance of understanding how catalysts and supporting materials aid chemical reactions is vital to the search for cleaner and less costly ways to create, store, and use energy, as well as for new efficiencies within energy-intensive industrial processes. Catalysts can add speed, reduce feedstocks, remove pollutants, and perform other valuable tasks.

To achieve unprecedented levels of characterization, the team is combining powerful capabilities with diverse expertise. EMSL's ultrahigh-field nuclear magnetic resonance (NMR) spectroscopy capability—the largest collection of such instruments in the United States—is yielding experimental results that are integrated closely with onsite supercomputing tools. In addition to EMSL scientists, the campaign team has drawn experts from Pacific Northwest National Laboratory's Institute for Integrated Catalysis; the University of California, Berkeley; and Pennsylvania State University.

"That's what is most exciting about this campaign. We're bringing to the table a team of world-class catalysis scientists with an outstanding NMR group and computational power you can't find anywhere else," said Dr. Karl Mueller, an EMSL scientist and PNNL Laboratory Fellow. "Because of the high caliber of the research team and the resources we're using, I'm confident we will gain an entirely new level of understanding in the area of catalytic materials and processes. And, this is only confirmed by the results we're already seeing."

The 29Si CP-CPMG MAS-NMR spikelet pattern provides information about the local electromagnetic environment of the Si atoms in the probe molecule and how it has reacted with the catalyst surface.

EMSL's new 850-MHz wide-bore NMR system and a set of novel in situ NMR probes designed and built at EMSL are central to the catalysis campaign. These resources, which were funded by the American Recovery and Reinvestment Act (ARRA), are dedicated specifically to catalysis-related experiments. The probes are designed to hold samples in environments that replicate the temperatures, pressures, gas flows, and other conditions catalysts face in real-world applications, allowing scientists to more closely link fundamental observations with applied technologies.

Initial meetings and experimental plans focused on confirming that the campaign's NMR experiments are highly relevant and comparable to catalysts operating in industrial-scale settings. Working to anticipate and avoid scale-related problems is critical, says Mueller, and necessary for results that maximize societal benefit.

"Anytime you're doing in situ spectroscopic work at small scales to observe reactivity, it's important to determine how comparable your experimental conditions are to the industrial-scale reactions. Another term we use is operando, which refers to experiments that are truly relevant for specific operating conditions," he added.

As team members, such as UC Berkeley's Dr. Enrique Iglesia, visit EMSL to plan experiments, EMSL scientist Dr. Nancy Washton has been working to bridge the gap between NMR and computation. By using the 850-MHz system, she has gathered robust and reliable data with exceptional sensitivity, which can then be compared to computations. Dr. Amity Anderson, a computational chemist in EMSL, uses these data to help predict the NMR parameters the team will measure in subsequent experiments and to garner the most information about reactive sites on the catalysts and surrounding materials.

An example of these early results on catalytic support materials, α-alumina and γ-alumina, are shown in Figure 1. Both aluminas are used as catalyst supports, but γ-alumina also is recognized to possess catalytic activity separate from that of any embedded catalyst (e.g., palladium, platinum, etc.). The team used a highly sensitive probe molecule that preferentially attaches to well-defined surface sites. They discerned the dissimilarity between the two aluminas through the measurement of 29Si chemical shifts of the probe molecule.

"We now have a direct NMR method for interrogating the surface reactivity of catalytic materials," Washton explained. "For specific forms of reactivity this method accords predictive ability, thereby decreasing the cost and time to market for new materials, especially those related to fuel production."

Mueller added: "We've only been able to achieve these results because of the high field strength and sensitivity of the 850-MHz spectrometer and associated probes. And, we're only able to confidently take the next steps with the custom in situ probes because of the integration between NMR and computation."

Like all of EMSL's experimental and computational tools, the 850-MHz NMR system and custom probes are open for use to the global scientific community through EMSL's peer-reviewed user proposal process. The campaign team currently is drafting the first scientific publication based on their new results, which will be submitted to a peer-reviewed journal this fall. In addition, team members plan on disseminating their findings while attending fall meetings of the American Chemical Society (ACS) and the Materials Research Society (MRS).