Individual atoms of palladium, represented by the yellow peaks, in the surface of copper help break hydrogen molecules into two atoms, facilitating important chemical reactions.
MEDFORD, US: Hydrogenation is a key process in a large number of industries, such as oil refining, where it is used to turn crude oil into gasoline. Hydrogenation happens due to the presence of a catalyst, usually a metal, such as nickel or palladium, or an alloy, which allows the hydrogen atoms to bind with other molecules. Typically, metal alloys are mixtures of cheap common metals, such as nickel, and expensive precious metals, such as platinum or palladium. However, it is hard to produce alloys that are selective hydrogenation catalysts, which are able to attach the hydrogen atoms to specific sites on a molecule.
Scientists at Tufts have found a way to create a selective hydrogenation catalyst by scattering single atoms of palladium onto a copper base. This catalyst requires less of the expensive metal, and the process is greener, too, offering potentially significant economic and environmental benefits. Led by Charles Sykes, Associate Professor, Tufts University, the group of researchers heated up very small amounts of palladium to almost 1,000 degrees Celsius. At that temperature, the metal evaporated like a gas, so that single atoms were released. These atoms, less than half a nanometre wide, embedded themselves into a copper metal surface about three inches away.
Using a scanning tunneling microscope, which can capture pictures of objects at the atomic level, the researchers verified that single palladium atoms had indeed embedded themselves at scattered intervals in the copper. In a conventional metal catalyst, by contrast, palladium is used in clumps 5 to 10 nanometre wide. It is less environmentally friendly as well, because of the energy that must be used to extract the additional necessary palladium from raw ore.
According to Georgios Kyriakou, Assistant Professor, Tufts University, the new catalyst also behaves differently. He helped determine that the single atom alloy was more effective in catalyzing hydrogenation than denser mixtures of palladium and copper. “In the face of precious metals scarcity and exorbitant prices, these systems are promising in the search for sustainable global solutions,” said Maria Flytzani-Stephanopoulos, Professor, Tufts University , whose lab is studying the effectiveness of the single-atom process.
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