Researchers find isolated Pd atoms efficient low-temperature catalysts to convert CO in automotive exhaust
Researchers have found that isolated palladium atoms on γ-alumina supports along with a small amount of lanthanum oxide can efficiently turn the carbon monoxide in automotive exhaust into carbon dioxide at temperatures as low as 40 ˚Celsius, potentially reducing toxins emitted by vehicle exhaust—especially at start-up—and replacing or reducing the need for platinum in automotive catalytic converters.
The catalyst activity can be regenerated by oxidation at 700 °C in air. The high-temperature stability and regenerability of these ionic palladium species make this catalyst system of potential interest for low-temperature exhaust treatment catalysts, the researchers suggested in a recent paper in the journal Nature Communications.
Most of the pollutants from a modern automobile are emitted during the first 30 seconds of starting a car, when the catalyst is still being warmed. At low temperatures, carbon monoxide builds up on the catalyst, decreasing its efficiency. This research shows a way to make the catalyst more effective at lower temperatures by enhancing its reactivity.—Prof. Abhaya Datye, corresponding author and Prof. of Chemical and Biological Engineering at the University of new Mexico
A research roadmap established by the US Department of Energy (DOE) sets 150 ˚C as a target for achieving removal of pollutants from exhaust. Datye and his colleagues are working to establish a way for the catalytic converters to work efficiently at or below that target temperature.
The team found that isolated palladium atoms can be catalytically active on industrially relevant γ-alumina supports. Adding lanthanum oxide—long known for its ability to improve alumina stability—to the alumina helped stabilize the isolated palladium atoms.
The team used aberration-corrected scanning transmission electron microscopy and operando X-ray absorption spectroscopy to confirm the presence of intermingled palladium and lanthanum on the γ-alumina surface.
The lanthana is itself present as isolated single atoms, and it helps trap palladium atoms. The isolated palladium atom species show unusual reactivity for carbon monoxide oxidation at low temperatures, since the palladium in ionic form has a lower binding energy and hence is not poisoned by carbon monoxide.
The finding that isolated palladium species can be stabilized on an industrially relevant support such as alumina, the authors suggest, is of potential interest to the field of automotive catalysis and to other heterogeneous catalysts and also for improved understanding of sintering and dispersion. Single isolated transition metal atoms provide the ultimate in atom efficiency, in the context of reducing the demand for costly precious metals such as platinum or palladium.
The paper was prepared through collaboration between the Dept. of Chemical and Biological Engineering, the Center for Microengineered Materials and the Department of Chemistry and Chemical Biology at the University of New Mexico. Other collaborators include scientists from the Research Institute of Photocatalysis, State Key Laboratory of Photocatalysis on Energy and Environment, Fuzhou University, Fuzjou, China; Chemical Science and Engineering at Argonne National Laboratory; the Institute for Integrated Catalysis, Pacific Northwest National Laboratory; Dept. of Physics, New Mexico State University; Materials Science and Technology Division, Oak Ridge National Laboratory; the School of Chemical Engineering at Purdue University; and the Department of Chemical Engineering, UNIST, Ulsan, Korea.
Research funds were supplied by the US Dept. of Energy; the National Natural Science Foundation of China; and the US National Science Foundation.
Eric J. Peterson, Andrew T. DeLaRiva, Sen Lin, Ryan S. Johnson, Hua Guo, Jeffrey T. Miller, Ja Hun Kwak, Charles H. F. Peden, Boris Kiefer, Lawrence F. Allard, Fabio H. Ribeiro & Abhaya K. Datye (2014) “Low-temperature carbon monoxide oxidation catalysed by regenerable atomically dispersed palladium on alumina” Nature Communications 5, Article number: 4885 doi: 10.1038/ncomms5885