Recent findings from a systematic study reveal the optimal combination of metals to increase the catalytic removal of NOx from diesel engine exhaust emissions. Credit: Ella Maru Studio
Smog-producing chemicals could be virtually removed from the exhaust pipes of cars and diesel vans, using a new exhaust catalyst concept developed at KAUST. After systematically studying multiple catalyst compositions, the research team identified the ideal atomic recipe for catalytically removing NOx from vehicle emissions. The findings, published in Communications of natureresolves an ongoing debate about additive atoms in the catalyst mixture.
Recent developments in high-efficiency engine design, along with tightening vehicle emission regulations, require improved engine exhaust catalysts. The current generation NOx catalysts for small diesel engines work optimally above 200 degrees Celsius. Catalysts that operate at lower temperatures are now needed. These catalysts must quickly remove NOx after a cold start and partner with new low temperature combustion engines.
To develop a new generation of improved NOx catalysts, the car emission control company Umicore partnered with a research team from the KAUST Catalysis Center, led by Javier Ruiz-Martínez, to optimize the design of the catalyst.
“We have researched manganese-based materials for their good performance and low cost,” explains Ruiz-Martínez. Manganese-based NOx catalysts have commonly used cerium as a dopant, although there was no consensus on the role of cerium in NOx removal. “The best way to develop new catalysts is to first understand how these materials work,” says Ruiz-Martínez. Thus, the team produced a series of catalysts, which incorporated varying amounts of cerium, to resolve the debate.
The team first established methods to produce each catalyst with a homogeneous nanostructure to allow a comparison between them. “After making sure the catalyst materials were as we designed, we looked for correlations between catalytic activity and the amount of cerium and manganese,” says Ruiz-Martínez. After considering the differences in the surface of the catalyst, the team showed that the presence of cerium reduced the catalytic activity of the manganese atoms.
In previous studies where cerium appeared to increase catalytic NOx removal, the apparent positive effect of cerium disappeared once the equipment considered its impact on the catalyst surface. However, cerium had a benefit: it suppresses an unwanted side effect that produces N2O. Because N2O formation probably requires the participation of two neighboring manganese sites, the addition of cerium can dilute the number of surface manganese sites and thus suppress the reaction.
“Our findings show that the design of more active catalyst materials requires the maximization of manganese atoms on the catalyst surface and that these manganese atoms are spaced atomically to prevent N2O formation,” says Ruiz-Martínez. “We are now designing catalysts that expose atomically dispersed manganese to the surface, and the results are extremely promising.”
Manganese leaves its mark on drug synthesis More information: Lieven E. Gevers et al, Unraveling the structure and role of Mn and Ce for NOx reduction in application-relevant catalysts, Communications of nature (2022). DOI: 10.1038 / s41467-022-30679-9 Provided by King Abdullah University of Science and Technology
Citation: A systematic study resolves the debate over the design of the car exhaust catalyst (2022, June 6) recovered on June 6, 2022 from
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