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A novel method for improving catalyst performance has emerged from the study of car exhaust, with implications for reducing the reliance on costly and rare metals in catalytic converters and various emission control technologies.
In a publication in Nature, an international collaboration of scientists uncovered an unexpected chemical reaction that takes place when hot car exhaust, rich in nitrogen oxides and carbon monoxide, interacts with catalyst materials. The findings suggest that this reaction can be harnessed to enhance catalytic activity significantly. Catalysts are crucial for accelerating chemical reactions, making them central to various industrial processes.
The study demonstrated that exposure to hot exhaust promotes the formation of two-dimensional, nano-sized clusters of ceria, a key component in catalyst formulations. These densely arranged clusters increase the available surface area for reactions, thereby boosting catalytic efficiency. Additionally, this method results in a higher number of loosely bound oxygen ions around cerium atoms, which enhances the performance of reactions that require the transfer of oxygen.
According to Yong Wang, one of the lead authors of the study and a Regents Professor at Washington State University’s Gene and Linda Voiland School of Chemical Engineering and Bioengineering, “They function like an oxygen sponge, allowing for easier activation of oxygen, which is essential for oxidation reactions involving hydrocarbons and carbon monoxide. This presents an opportunity for designing catalysts capable of supporting multiple reactions.” The chance discovery revealed an up to tenfold increase in catalytic activity.
“Serendipity played a role in this discovery. Occasionally, scientific exploration leads us to unexpected yet impactful outcomes,” Wang noted. He is also concurrently affiliated with the Pacific Northwest National Laboratory (PNNL).
Ongoing advancements in catalytic converters and emission control technologies remain a priority for researchers, especially since these systems tend to lose effectiveness over time. To meet stringent emission standards, manufacturers often need to incorporate additional quantities of precious metals, including rhodium, platinum, or palladium, as catalysts degrade.
A long-standing puzzle in the industry has been that even though nano-sized metal materials in catalytic converters are known to aggregate when subjected to high-temperature and harsh exhaust conditions, they still demonstrate better durability than anticipated.
Konstantin Khivantsev, a chemical engineer and staff scientist at PNNL, pointed out, “Our observations suggested that ceria particle size increases would typically lead to a drastic reduction in performance, but this was not the case. A previously unrecognized process contributed to enhanced dispersion and catalytic effectiveness.”
The research team, which included members from WSU, PNNL, the University of New Mexico, the University of Sofia in Bulgaria, and Purdue University, initially sought to artificially age a catalyst to evaluate its performance. Instead of the traditional method involving just water, they exposed the catalyst to hot car exhaust for several hours. Contrary to expectations, the catalyst’s performance improved rather than faltered.
Abhaya Datye, Distinguished Regents Professor Emeritus at the University of New Mexico and a co-author of the study, remarked, “The initial hypothesis indicated a decline in activity, yet the results defied our expectations. This anomaly prompted us to verify our findings through repeated experiments, leading us to explore the underlying science.”
Through their investigation, researchers discovered that the catalysis process benefitted from short bursts of activity induced by the high temperatures present in car exhaust, contrary to the assumptions previously held in the field. With this newfound understanding, the researchers propose to harness this pre-activation process intentionally to establish a reactive state at the onset of a catalyst’s operational life.
The implications of this innovative treatment technique could include significant reductions in the quantities of precious metals like rhodium used in catalytic converters, translating to substantial cost savings. For instance, the typical cost of rhodium in a single catalytic converter can reach approximately $800.
János Szanyi, a staff scientist at PNNL and a corresponding author, explained, “The presence of atomically thin patches of ceria created through the dispersion of ceria nanoparticles effectively interacts with precious metals like rhodium and platinum. This interaction helps maintain catalyst activity under the extreme thermal conditions of vehicle exhaust.”
The research team is currently testing their catalyst treatment on a laboratory scale and collaborating with industry partners to evaluate its performance in real-world vehicle conditions. This investigation is grounded in fundamental science and has received backing from the U.S. Department of Energy’s Office of Science, specifically within the Basic Energy Sciences and Catalysis Science program. Support for research at PNNL has also come through the Energy Efficiency and Renewable Energy Vehicle Technologies Office.
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