Ceramic that breathes oxygen at lower temperatures helps us breathe cleaner air

Although much of the discourse on reducing vehicle emissions focuses on electric vehicles (EVs), their sales remain low – EV vehicles will only account for 1% of car purchases in Japan in 2021. Meanwhile , the European Union should adopt stricter emission standards. standards in the near future. This makes improving the performance and functionality of exhaust gas purification catalysts for gasoline or diesel vehicles a key part of the transition to carbon neutrality.

Almost all petrol or diesel cars are equipped with catalytic converters which remove harmful hydrocarbons, carbon monoxide and nitrogen oxide and convert them into safer gases such as nitrogen, carbon dioxide and steam. of water. Toxic gases circulate through a honeycomb structure, covered with exhaust gas purification catalysts.

Oxygen storage capacity (OSC) ceramics play a crucial role in the purification process. They help remove harmful gases and prevent precious metals in catalytic converters from swelling, which degrades their purification capabilities.

Oxygen storage ceramics in an exhaust gas system. ©Hitoshi Takamura

However, to improve their potential, a lower operating temperature is required. But scientists have struggled to achieve this because reducing the temperature to less than 500 ºC results in slower ion diffusion.

Now, a research group from the Graduate School of Engineering of Tohoku University has developed a cerium-zirconium (Ce-Zr)-based oxide with excellent OSC at 400 ºC by controlling its crystal structure. OSC at 400 ºC was higher than conventional materials by a factor of 13.5, even without precious metal catalysts.

“Key to our success was the introduction of a tiny amount of transition metals, such as iron, into the Ce-Zr-based oxides,” said Professor Hitoshi Takamura, leader of the research group.

“Transition metal doping” had two notable effects on the oxides. It accelerated the diffusion of oxygen by facilitating the formation of oxygen vacancies and promoting the ordering of cations.

“The order of cations organizes the crystal structure and makes oxygen easily released,” Takamura explained.

Oxygen storage ceramics in an exhaust gas system. ©Hitoshi Takamura

Iron doping reduced the ordering temperature of the cations, which in turn allowed more surface area for Ce-Zr based oxides. This improved their durability and their ability to purify toxic gases.

In the future, Takamura and his group hope to test the material by loading it with palladium on honeycomb carriers.

Details of the group’s research were published in the Journal of Materials Chemistry A on September 27, 2022. And the article was chosen for the cover of the journal.

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Release details:

Title: Low-temperature synthesis of Ce-Zr-based oxide ordered by cations via an intermediate phase between Ce and Fe

Authors: Kazuto Murakami, Yoko Sugawara, Junki Tomita, Akihiro Ishii, Itaru Oikawa and Hitoshi Takamura

Journal: Journal of Materials Chemistry A

DOI: 10.1039/d2ta05068d

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