Pioneering new tool will spur advances in catalysis

For decades, catalysts have been unsung heroes in daily life. These workhorses transform a starting material into a product or fuel with lower energy, like the yeast in bread making and human-made catalysts for converting raw materials into fuels more efficiently and sustainably. A promising class of these helpful substances, called single atom catalysts, has emerged, and researchers need new methods to better understand them. More specifically, they want to know how the structure of the sites where chemical reactions occur, called active sites, affects the catalyst’s ability to speed up the chemical reaction rate, known as the activity. 

In an important step forward, researchers from the Stanford Synchrotron Radiation Lightsource (SSRL) at the Department of Energy’s SLAC National Accelerator Laboratory collaborated with a team from the University of California, Davis (UC Davis), to develop a new software tool that can provide more quantitative details about the structure of the active sites in single atom catalysts in much less time, compared to current methods. The results were published in Chemistry–Methods.

Normally, a catalyst uses an inert support to stabilize nanometer-sized clusters of metal atoms, or metal nanoparticles. During catalysis, only the surface atoms act as active sites, leaving atoms in the interior of the nanoparticle unused. To maximize the utilization of each metal atom, researchers came up with a promising idea – single atom catalysts, where individual metal atoms are dispersed onto the support. 

In designing and developing these catalysts, researchers need to understand the structure of the active sites so they can relate it to the activity. To learn more about the structure, the team used single platinum atoms stabilized on a magnesium oxide support as a case study for similar single atom catalysts. The study’s lead author Rachita Rana, who recently received her PhD from UC Davis, utilized a technique called extended X-ray absorption fine structure (EXAFS) spectroscopy, which reveals the average environment around the atom in the active site, such as the number and distance of neighboring atoms. Traditionally, with EXAFS data, researchers evaluate tens to hundreds of candidate structures before selecting the best fit. Instead, Rana proposed automating the analysis process by combining theoretical calculations, called density functional theory, and EXAFS. The first version of the software, QuantEXAFS, determined the structure for one kind of atom, platinum atoms in this case. 

In reality, catalysts usually have both single atoms and nanoparticles. Building upon QuantEXAFS, Rana expanded the capabilities of the code to determine the fractions of these two forms, giving more specific information about the structure. “MS-QuantEXAFS not only helps identify the active sites, but also quantifies the percentage of a specific site and automates the entire data analysis process,” she said. “If you’re doing this manually, it typically could take you anywhere from a few days to months. With MS-QuantEXAFS, you could potentially do this analysis overnight on a local computer.” 

The team would next like to prepare and release MS QuantEXAFS to the scientific community. “This tool has a lot to offer to catalysis researchers,” said Rana. Co-author and Distinguished Scientist at SSRL, Simon R. Bare, agrees, adding that they also plan to include it in training classes, especially for the next generation of students.

The DOE Office of Science supported this research. SSRL is a DOE Office of Science user facility.