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Catalytic converters have been used in the US since the 1970s as a way to clean up pollutants from vehicle exhaust. In the catalytic process, rare metals such as platinum, are used in a chemical reaction to convert carbon monoxide and other pollutants to non-toxic carbon dioxide, nitrogen, and water.

As cars have become more fuel-efficient, however, they use less energy and the temperature of the exhaust gases is lower, which makes it harder to clean up the pollutants. The US Department of Energy has set a goal of removing 90% of harmful emissions at 150 degrees Celsius or lower.

In addition to high reactivity at low operating temperatures, thermal durability is essential for the catalysts to survive the harsh conditions encountered in automotive exhaust.

Now, researchers at Washington State University, University of New Mexico, Eindhoven University of Technology, and Pacific Northwest National Laboratory report developing a catalyst that can both withstand high temperatures and convert pollutants at near room temperature.

They report on their work in an open-access paper in the journal Nature Communications.

The catalyst the researchers developed is based on the activation of single atoms of platinum (Pt) supported on cerium oxide (CeO₂). While their catalyst outperforms current technology, it also reduces the amount of platinum required, which would lower overall costs.

Synthesis of single-atom Pt/CeO₂ with improved reducibility and its transformation into an active catalyst. The Pt/CeO₂ single-atom catalyst (SAC) is reduced and forms Pt nanoparticles. This active state of the catalyst readily provides oxygen to react with CO adsorbed on Pt nanoparticles, preventing CO poisoning. Red: ionic Pt, green: metallic Pt. Pereira-Hernández et al.

The industry wants to make use of every single atom of the precious metals, which is why single-atom catalysis has attracted increased attention.

—Abhaya Datye, a distinguished professor at UNM’s Department of Chemical and Biological Engineering

In their latest work, the researchers first ensured their catalysts were thermally stable, trapping platinum ions on a cerium oxide support at very high temperatures. Their synthesis method caused the platinum atoms to strongly bond to their support. They then activated the catalyst in carbon monoxide at about 275 degrees Celsius.

To our surprise, we discovered that the high temperature synthesis made the ceria more easily reducible, allowing it to provide a key ingredient—oxygen—to active sites.

—Yong Wang, Voiland Distinguished Professor in the Gene and Linda Voiland School of Chemical Engineering and Bioengineering at WSU

The activated oxygen was then able to remove pollutants at near room temperature at the platinum sites.

This research directly addresses the 150-degree challenge identified by the US Department of Energy and by automobile companies. The discovery of oxygen activation at near room temperature is extremely useful, and this finding could have a significant impact on the technology of exhaust emission control.

—Yong Wang

The researchers now plan to study the performance of single-atom catalysts with other organic compounds and pollutants. The work was funded by the USDepartment of Energy’s Office of Basic Energy Sciences and Netherlands Research Center for Multiscale Catalytic Energy Conversion.

Resources

• Xavier Isidro Pereira-Hernández, Andrew DeLaRiva, Valery Muravev, Deepak Kunwar, Haifeng Xiong, Berlin Sudduth, Mark Engelhard, Libor Kovarik, Emiel J. M. Hensen, Yong Wang & Abhaya K. Datye (2019) “Tuning Pt-CeO₂ interactions by high-temperature vapor-phase synthesis for improved reducibility of lattice oxygen” Nature Communications volume 10, Article number: 1358 doi: 10.1038/s41467-019-09308-5