Left Alone, Palladium Atoms Get the Job Done

Isolated atoms quickly tackle carbon monoxide, potentially reducing lean-burn engine emissions

(October 2014)

Isolated palladium atoms on γ-alumina supports along with a small amount of lanthanum oxide can efficiently turn carbon monoxide into carbon dioxide at 40 degrees Celsius, potentially reducing toxins emitted by vehicle exhaust and replacing or reducing the need for platinum in catalytic converters. Enlarge Image.

Results: Whether driving a car with a lean burn engine or a conventional one, your catalytic converter struggles to reduce emissions in the first 30 seconds after you start the car. Your platinum-based converter does not work well in colder temperatures, before the engine warms up. Scientists including two at Pacific Northwest National Laboratory discovered that isolated palladium atoms could reduce emissions under these conditions. They showed that the palladium atoms efficiently turn carbon monoxide into carbon dioxide at 40 degrees Celsius. The multi-year study appears in Nature Communications.

Why It Matters: Catalytic converters, first seen in the U.S. automotive market in the mid-1970s, use platinum to reduce the toxins emitted. For scientists and automotive manufacturers, the challenge is to use less platinum or a more readily available metal. Catalysis by single isolated atoms would reduce the amount of metal needed and would be more efficient. This study shows that isolated palladium atoms on γ-alumina supports along with a small amount of lanthanum oxide can get the job done.

Methods: The researchers conducted experiments and performed density functional theory calculations to understand the activity of palladium atoms on γ-alumina supports. The team used operando X-ray absorption spectroscopy and aberration-corrected scanning transmission electron microscopy. At Pacific Northwest National Laboratory's Institute for Integrated Catalysis, Dr. Ja Hun Kwak (now a professor at Ulsan National Institute of Science and Technology (UNIST) in South Korea) and Dr. Charles Peden prepared parallel sets of samples of palladium/alumina and lanthanum/alumina to confirm the presence of intermingled palladium and lanthanum on the γ-alumina surface.

What's Next? At the Institute for Integrated Catalysis at PNNL and elsewhere, research continues into designing catalysts that will remove pollutants from vehicle exhaust emissions operating at or below the DOE target of 150 degrees Celsius or about 300 degrees Fahrenheit.

Acknowledgments

Sponsors: The University of New Mexico authors acknowledge funding for this work provided by the DOE Office of Science grant. S.L. thanks the National Natural Science Foundation of China. R.S.J. and H.G. thank the U.S. National Science Foundation. Materials Research Collaborative Access Team (MRCAT) operations are supported by DOE and the MRCAT member institutions. J.T.M., F.H.R., C.H.F.P., and J.H.K. were supported by the DOE Office of Science, Office of Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Division

Research Area: Chemical Sciences

User Facilities:  Advanced Photon Source; STEM imaging was performed at the High Temperature Materials Laboratory, operated by Oak Ridge National Laboratory and supported by DOE, EERE Office of Vehicle Technologies; and EMSL, a national scientific user facility sponsored by DOE's Office of Biological and Environmental Research

Research Team: Eric J. Peterson, Andrew T. DeLaRiva, Ryan S. Johnson, Hua Guo, Boris Kiefer, and Abhaya K. Datye, University of New Mexico; Sen Lin, Fuzhou University, China; Jeffrey T. Miller, Argonne National Laboratory; Lawrence F. Allard, Oak Ridge National Laboratory; Fabio H. Ribeiro, Purdue University; Ja Hun Kwak and Charles H.F. Peden, Pacific Northwest National Laboratory

Reference: Peterson EJ, AT DeLaRiva, S Lin, RS Johnson, H Guo, JT Miller, JH Kwak, CHF Peden, B Kiefer, LF Allard, FH Ribeiro, AK 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