To improve fuel efficiency, advanced combustion engines are being designed to minimize the amount of waste heat in the exhaust. As a result, future generations of exhaust after-treatment catalysts must perform at temperatures that are 100 °C lower than current catalysts.
Researchers at Washington State University, Pacific Northwest National Laboratory and the University of New Mexico have now devised a catalyst capable of reducing pollutants at the lower temperatures expected in advanced engines. Their work, published this week in the journal Science, presents a new way to create a more powerful catalyst while using smaller amounts of platinum—the most expensive component of emission-control catalysts.
In this study, we demonstrate how atomically dispersed ionic platinum (Pt2+) on ceria (CeO2), which is already thermally stable, can be activated via steam treatment (at 750 °C) to simultaneously achieve the goals of low-temperature carbon monoxide (CO) oxidation activity while providing outstanding hydrothermal stability.—Nie et al.
The researchers designed a catalyst that could endure engine exhaust temperatures of up to 800 ˚C encountered under high engine loads. Yet the catalyst would still have to work when an engine is started cold and must clean up the exhaust before reaching 150 ˚C, significantly lower than current systems. The lower operating temperatures during cold start are due to increasing fuel efficiency in advanced combustion engines, which leaves less energy in the tailpipe exhaust, said Abhaya Datye, a distinguished professor at the University of New Mexico and a study co-author.
The recent findings grew out of a collaboration between research groups led by Yong Wang, who holds a joint appointment in Washington State University’s Gene and Linda Voiland School of Chemical Engineering and Bioengineering and the Pacific Northwest National Laboratory, and Datye’s catalysis group at New Mexico.
The work builds on research, published in Science last year, in which the Wang and Datye groups found a novel way to trap and stabilize individual platinum atoms on the surface of cerium oxide, a commonly used component in emissions control catalysts. The so-called single-atom catalyst uses platinum more efficiently while remaining stable at high temperatures. Platinum typically trades at prices close to or even greater than gold.
For their latest paper, the researchers steam-treated the catalyst at nearly 1,400 degrees Fahrenheit. This made the already stable catalyst become very active at the low cold-start temperatures.
We were able to meet the challenges of both the high-temperature stability and the low-temperature activity. This demonstration of hydrothermal stability, along with high reactivity, makes it possible to bring single-atom catalysis closer to industrial application.—Yong Wang
Multiple types of spectroscopy and electron microscopy capabilities available at EMSL, the Environmental Molecular Sciences Laboratory, a DOE Office of Science user facility on the PNNL campus, allowed the scientists to understand the catalyst surface at the atomic level and provide mechanistic insight into how oxygen vacancies migrate to the surface of the cerium oxide, creating pathways for highly active carbon monoxide conversion.
The work was funded by DOE’s Office of Science, Basic Energy Sciences and Office of Energy Efficiency and Renewable Energy’s Vehicle Technologies Office.
L Nie, D Mei, H Xiong, B Peng, Z Ren, XIP Hernandez, A DeLaRiva, M Wang, MH Engelhard, L Kovarik, AK Datye, and Y Wang (2017) “Activations of Surface Lattice Oxygen in Single-Atom Pt/CeO2 for Low-Temperature CO Oxidation.” Science doi: 10.1126/science.aao2109