Single-atom catalysts transform hydrogenation, improving food and fuel production

A chemical reaction that’s vital to a range of commercial and industrial goods may soon be initiated more effectively and less expensively thanks to a collaboration that included Oregon State University College of Engineering researchers.

The study, published in Nature, involves hydrogenation—adding the diatomic hydrogen molecule, H₂, to other compounds.

“Hydrogenation is a critical and diverse reaction used to create food products, fuels, commodity chemicals and pharmaceuticals,” said Zhenxing Feng, associate professor of chemical engineering. “However, for the reaction to be economically viable, a catalyst such as palladium or platinum is invariably required to increase its reaction rate and thus lower cost.”

Feng, OSU doctoral students Alvin Chang and Mason Lyons and researchers at four institutions in China took a deep dive into single-atom catalysts; a catalyst is anything that speeds the rate of a chemical reaction without being consumed by the reaction, and a single-atom catalyst is one in which the metal catalytic sites exist as isolated single atoms on a supporting substrate.

“SACs are a rising star among hydrogenation catalysts and demonstrate excellent catalytic activities compared to nanoparticle catalysts,” Feng said. “Interactions between the metal catalyst and support material lead to unique synergies that improve catalytic activity and stability, but the reason for this enhanced performance had not been understood.”

In a project led by collaborators at the Chinese Academy of Sciences and the University of Science and Technology of China, researchers created and characterized 34 palladium SACs on 14 semiconductor supports.

Advanced X-ray, infrared and electrochemical characterization techniques showed the SACs’ effectiveness depended on how well a substrate could accept electrons, a connection that was consistent and predictable.

“The catalytic abilities of palladium SACs have a universal linear relationship with the molecular orbital position of their supporting substrates,” Feng said. “This opens a new avenue for the screening of metal-support pairs for high activity and stability. We also found that this molecular orbital position can be tuned by reducing support particle size, leading to SACs with record high activities and excellent stabilities.”

For this study, researchers looked at the semihydrogenation of acetylene in excess ethylene, a common industrial process. In hydrogenation, hydrogen molecules are added to unsaturated bonds in organic compounds, converting them to saturated compounds. For example, hydrogenation is used to convert vegetable oils, which are unsaturated fats, into margarine and shortening.

Hydrogenation is also important for the refining of petroleum products, including converting alkenes like ethylene into alkanes to make cleaner-burning fuels such as propane and butane.