AsianScientist (May. 18, 2026)–Methane traps about 80 times more heat in the atmosphere than carbon dioxide over 20 years. Industrial exhaust systems remove it by passing gases over metal oxide catalysts that convert the gas into carbon dioxide and water. Central to this process is ceria (CeO2), a compound of cerium and oxygen, valued for its unique ability to store and release oxygen. However, the exact mechanism of how oxygen moves from within the ceria structure to the reaction surface has remained poorly understood.
Now, a study in Nature Communications by researchers at the Korea Advanced Institute of Science and Technology (KAIST) and Seoul National University reveals that ceria nanoparticles switch between two distinct strategies of oxygen transfer depending on particle size.
Ceria operates via the Mars-van Krevelen mechanism, a process where the catalyst uses its own internal oxygen to oxidise an incoming molecule, leaves a vacancy behind, then refills that vacancy. It can do this either by grabbing oxygen from the surrounding gas or by drawing on reserves stored deeper in the crystal structure. Previous studies treated these two replenishment routes as interchangeable, and separating them is what makes this study distinctive.
To isolate the pathways, the team engineered catalysts containing isolated ceria domains measuring 3.7, 5.6 and 7.3 nanometres on alumina supports. Platinum was restricted to single atoms to prevent it from activating oxygen independently, ensuring that all observed chemical changes could be attributed to ceria alone.
The team probed each catalyst using carbon monoxide oxidation experiments, ambient-pressure X-ray photoelectron spectroscopy and oxygen isotope tracing, which tracks whether the product molecule incorporates oxygen from the gas or from the crystal.
The experiments showed that small and large ceria domains behaved differently based on environmental oxygen levels. Under oxygen-rich conditions, the 3.7 nm catalyst outperformed larger particles, capturing 1.5 micromoles of gaseous oxygen per square metre of ceria surface to fill vacancies rapidly. Under oxygen-poor conditions, the 7.3 nm catalyst surged ahead by transferring oxygen outward from its subsurface layers, confirmed by spectroscopy showing oxygen being drawn from deeper within the crystal at high temperatures. In essence, smaller domains behave like sprinters, rapidly grabbing oxygen from the air, whereas larger domains run like endurance runners, drawing steadily on internal reserves.
The simulations revealed a straightforward structural reason for the differences. Smaller domains carry a higher density of uncoordinated surface sites, essentially surface gaps that serve as preferred landing points for incoming oxygen molecules. Conversely, larger domains offer fewer such sites but possess a deeper subsurface reservoir that migrates outward as surface oxygen is depleted.
“This research clearly distinguishes the two core mechanisms of how oxygen operates in catalysts for the first time,” said Hyunjoo Lee, a professor at KAIST’s Department of Chemical and Biomolecular Engineering.
The researchers applied these findings to methane oxidation. Since methane combustion operates under oxygen-rich conditions, the 3.7 nm domains were expected to excel, and they did, achieving higher methane conversion at lower temperatures than larger ceria systems.
Importantly, the performance advantage held even under humid conditions that typically reduce catalytic activity in industrial settings, while requiring significantly less precious metal.
The work establishes that catalyst performance depends not only on how much oxygen a material can store, but also on how efficiently oxygen moves through the material.
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Source: Korea Advanced Institute of Science and Technology (KAIST) ; Image: magnific
This article can be found at: Understanding oxygen transfer on ceria with Pt single atoms for surface reaction
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